The thermal oxidation is complex process including chain oxidation of hydrocarbon radicals, destruction of macro-chains and structure formation (cross-linking, crystallization). Thermal oxidation is accompanied by structural-physical processes leading to structure change (structural reconstruction) under the action of high temperature. The mechanism of these processes will depend on polymer's morphology and in its turn will influence on oxidation kinetics. The effect of polymer crystallites in vacuum and on air: the effect of high temperature may lead to perfection of crystallites structure, rise of temperature and melting heat, at the same time at long high temperature effect the destruction of chains occurs and crystallites and decomposed. There are the data demonstrating the influence of annealing temperature on relaxation parameters in polymer which allow concluding that there is significant change of structure of amorphous regions. At that the amorphous regions to a greater extent determine the particularities of oxidation radical reactions kinetics developing in them. With the aim of revealing of the role of structure (conformational set) of polymer macro-chains we also studied structure reconstructions, accompanying oxidation of oriented samples of PP with various extract degree. Structure parameters of PP: crystallites and amorphous regions, make it polymer heterophase system. These parameters of systems will determine localization of oxidation in zones having high segment mobility. In these Section is proposed a model for heterogeneous thermal oxidation of PP. Morphological irregularity of polymer results from the presence of crystalline and amorphous regions in the same polymer. This type of irregularity affects the regularities and rates of polymer oxidation. Crystallites are characterized by long-range order in the arrangement of macromolecules and of their monomeric units. Oxygen solubility in the crystallites is very low or zero, and

approximately equal to it (Shlyapnikov Yu. A. 1986; 1989).

In polyethylene formation of the products described in the following scheme ( Ranby B., Rabek J.F., 1978)

Polymer oxidation is accompanied by polymer chain destruction. When measuring the molecular weight of polymer, one can see only large remnants of the polymer chain, and if a short segment of the polymer chain takes place a few breaksthey will be treated as one scission .Denoting the probability of the scission of a macromolecule as a result of one step of chain reaction propagation 1, the probability that there is no scission is (1-1), and the probability of at least one scission resulting from b reaction steps proceeding in the same region (block) of the macromolecule is (Shlyapnikov Yu. A., 1989):

$$\mathbf{1}\_{\mathsf{b}^{\mathsf{b}}} = \mathbf{1}\_{\mathsf{-}} (\mathbf{1}\_{\mathsf{-}} \mathsf{b}^{\mathsf{l}})^{\mathsf{v}\_{\mathsf{b}}} \tag{65}$$

The rate of formation of such oxidatized regions (or blocks) of polymer chains is the sum of rates of chain initiation and of chain transition from one molecule to another. Supposing the latter to be directly proportional to the overall concentration of free radicals in the system, gets this:

$$\mathbf{W}\_b = \mathbf{W}\_o + \mathbf{k}\_{\rm tr} \left[ \mathbf{R} \mathbf{C}\_2 \mathbf{\*} \right] \tag{66}$$

where Wo is the chain initiation rate. It is assumed that the oxygen concentration is high enough and we can neglect reactions of R\* radicals. The rate of recorded scission formation is proportional to Wb, and if b=1 it is virtually equal to Wb. If the oxidation chains are long

In polyethylene formation of the products described in the following scheme ( Ranby B.,

Polymer oxidation is accompanied by polymer chain destruction. When measuring the molecular weight of polymer, one can see only large remnants of the polymer chain, and if a short segment of the polymer chain takes place a few breaksthey will be treated as one scission .Denoting the probability of the scission of a macromolecule as a result of one step of chain reaction propagation 1, the probability that there is no scission is (1-1), and the probability of at least one scission resulting from b reaction steps proceeding in the same

The rate of formation of such oxidatized regions (or blocks) of polymer chains is the sum of rates of chain initiation and of chain transition from one molecule to another. Supposing the latter to be directly proportional to the overall concentration of free radicals in the system,

 Wb = Wo + ktr [ RO2\*], (66) where Wo is the chain initiation rate. It is assumed that the oxygen concentration is high enough and we can neglect reactions of R\* radicals. The rate of recorded scission formation is proportional to Wb, and if b=1 it is virtually equal to Wb. If the oxidation chains are long

b = 1-(1-1) b (65)

region (block) of the macromolecule is (Shlyapnikov Yu. A., 1989):

Rabek J.F., 1978)

gets this:

enough, or ktr is small, the rate of polymer destruction, i.e. the rate of recorded scission formation, will be equal to Wo , i.e. to the rate of chain initiation. The rate of chain initiation plus the rate of chain branching are always equal to the rate of chain termination; thus the rate of chain scission is proportional to that of chain termination, and at b =1 is approximately equal to it (Shlyapnikov Yu. A. 1986; 1989).

## **3. The effects of structure on thermooxidation kinetics of polypropylene**

The direct correlation between initial structure of polymer and kinetics of oxygen absorption is consequent from our scheme ( Shibryaeva L.S.and al.,2003; 2006; 2010.)

The thermal oxidation is complex process including chain oxidation of hydrocarbon radicals, destruction of macro-chains and structure formation (cross-linking, crystallization). Thermal oxidation is accompanied by structural-physical processes leading to structure change (structural reconstruction) under the action of high temperature. The mechanism of these processes will depend on polymer's morphology and in its turn will influence on oxidation kinetics. The effect of polymer crystallites in vacuum and on air: the effect of high temperature may lead to perfection of crystallites structure, rise of temperature and melting heat, at the same time at long high temperature effect the destruction of chains occurs and crystallites and decomposed. There are the data demonstrating the influence of annealing temperature on relaxation parameters in polymer which allow concluding that there is significant change of structure of amorphous regions. At that the amorphous regions to a greater extent determine the particularities of oxidation radical reactions kinetics developing in them. With the aim of revealing of the role of structure (conformational set) of polymer macro-chains we also studied structure reconstructions, accompanying oxidation of oriented samples of PP with various extract degree. Structure parameters of PP: crystallites and amorphous regions, make it polymer heterophase system. These parameters of systems will determine localization of oxidation in zones having high segment mobility. In these Section is proposed a model for heterogeneous thermal oxidation of PP. Morphological irregularity of polymer results from the presence of crystalline and amorphous regions in the same polymer. This type of irregularity affects the regularities and rates of polymer oxidation. Crystallites are characterized by long-range order in the arrangement of macromolecules and of their monomeric units. Oxygen solubility in the crystallites is very low or zero, and

Thermal Oxidation of Polypropylene and Modified Polypropylene – Structure Effects 85

Differential scanning calorimetry, X-ray analysis, IR-spectroscopy, Electronic microscopy,

Bogayevskya TA, Monakhova TV, Shlyapnikov YA (1978) "On the connection between the

Chan J.H., Balke S.T. "The thermal degradation kinetics of polypropylene. *Polymer*

Denisov E.T., Miscavige N.I., Agabekov V.E..(1975). *The mechanism of liquid-phase oxidation*

Emanuel N.M., Buchachenko A.L.. (1982). *Chemical Physics of aging and stabilization of*

George A.G., Celina M., Lerf C. at al. (1997) "A Spreading Model for the Oxidation of Polypropylene" *Makromol. Chem., Macromol. Symp.*V 115. № 1. PP.69-92. Livanova N.M., Zaikov G.E. (1997) "The Initiation of Polypropylene Oxidation"*Intern. J.*

Makedonov Yu.V., Margolin A.L., & Rapoport N.Ya. and al. (1986)." On the causes of

Nakatani H., Suzuki S., Tanaka T. and al. "New kinetic aspects on the mechanism of

Popov A.A, Rapoport N.Ya, Zaikov G.E.. (1987). *Oxidation-oriented and stressed polymers*.

Ranby B., Rabek J.F (1978). *Photodegradation, Photo-oxidation and Photostabilization of*

Rapoport N.Ya., Mostovaya E.M., Zaikov G.E. (1986)."Simulation of Polychromatic

Roginsky, VA, Shanina EL, Miller, VB (1976) "The cellular effect of the decay of the

*Vysocomolek. Soedin*. V.28 A. № 7. PP.1380-1385. (In Russian )

changes in the effective rate constants continue and chain termination in the induction period of oxidation of isotropic and oriented isotactic polypropylene".

thermal oxidative degradation of polypropylenes with various tacticities". (2005).

Kinetics of the Propagation step of the Chain Oxidation Reaction in Strained Polypropylene Basing on the Rotational Isomers Model " *Vysokomolek. Soedin*. 28 А.

initiators in solid polypropylene" *Dokladii of the Academy of Sciences of USSR* V. 227.

crystallinity of polypropylene and the kinetics of the oxidation" *Vysocomolek. Soedin*.

*Degradation and Stability* (1997). V. 57.№ 2. Part. I. Molecular weight distribution. PP 113-125. Part II. Time-temperature superposition. PP.127-134. Part III.

*of oxygen-containing compounds*. Minsk: Science and Technology. P. 200.(In Russian)

**5.1.2 The research methods**

**6. List of abbreviations**  PE - polyetylene PP - polypropylene

PEHD - polyethylene of high density PELD - polyethylene of low density

V.20 B. № 6.PP.465-468.

Thermogravimetric analyses. PP.135-149.

*Polymeric. Mater.* V.36. №1. PP.23-31.

*Polymer.* V.46. № 11.PP.12366-12371.

Moscow: Khimiya. P. 168. (In Russian)

*Polymers*. Moscow: Mir. (In Russian).

№ 8. PP.1620 -1628. (In Russian)

*polymers.* Moscow: Nauka. P. 360. (In Russian )

ESR-study.

**7. References**

the R\* radicals present in crystalline zones of the polymer cannot transform into peroxide ones. On the other hand, these radicals can move inside the crystals by subsequent reactions R\* + RH. The capture of free radicals R\* by crystallites is equivalent to the kinetic chain termination if these radicals remain in the crystallites or recombine in them. It was shown (Shlyapnikov Yu.A., 1986) that if these radicals are only kept inside the crystallites for a certain time, this is equivalent to chain termination if the reaction is self – accelerated.

#### **4. Isotactic pp, modified by oil**

The given section is devoted to regularities of thermal oxidation and to structural reconstructions in the course of oxidation of model heterogeneous systems (Shibryaeva L.S., 2010). The change of destruction rate of PP chains in the presence of modifier may be explained by the change of mechanism of polymer oxidation. Increase of segment mobility of chain leads to increase of contribution of intermolecular transfer of kinetic chains of oxidation. As a result of this kinetic chains of oxidation become shorter and the number of breakages in macromolecules is increased. But in the case of destruction process acceleration at the stage of kinetic chains continuation at the expense of prevailing of intermolecular transfer in composition of hydroxyl containing products the single OH-groups will prevail. However analysis of products composition did not reveal prevailing of single OH-groups over block ones. Increase of chains mobility is observed not only in the case of PP with compatible additives, but also for uncompatible, nevertheless the rate of PP oxidation in its presence is reduced. The most probable reason of oxidation process acceleration in samples of PP with compatible additives, of the rise of PP chain destruction rate is joint oxidation (co-oxidation) of polymer and additives. There are two fundamental hypotheses concerning the mechanism of these reactions which can be derived from the present experimental knowledge of structure and reactivity of macroradicals. (1) Hypothesis of physical migration by which the reactions of reactants are controlled either by mobility of the chains or their parts (segments) with fixed free valence or by diffusion of the low-molecular products of macroradical decomposition, e.i. the so-called radical fragments. (2) Hypothesis of chemical migration by which the reactions of reactants are controlled by various reactions of macroradicals of low-molecular fragments.

#### **5. Experimental part**

The samples of Isotactic PP non-inhibited powder of polymerizate was purified by standard technique.

#### **5.1 The methods of investigation**

#### **5.1.1 Kinetics of oxidation**

The kinetics of oxidation of isotactic polypropylene was investigated in circulating apparatus with freeze-volatile products of oxidation at the temperature of liquid nitrogen. When the film thickness is less than 60 microns maximum rate of oxidation of the sample is proportional to its thickness. Consequently, at a thickness of less than 60 microns ( l<60 mcm) kinetic regime is realized, i.e. diffusion of oxygen is a rapid process and does not affect the rate of oxidation. On the contrary, for l > 200 microns oxidation occurs in the diffusion regime and the maximum speed calculated for 1 cm2 the surface is practically independent of the thickness.

#### **5.1.2 The research methods**

Differential scanning calorimetry, X-ray analysis, IR-spectroscopy, Electronic microscopy, ESR-study.

## **6. List of abbreviations**

## **7. References**

84 Polypropylene

the R\* radicals present in crystalline zones of the polymer cannot transform into peroxide ones. On the other hand, these radicals can move inside the crystals by subsequent reactions R\* + RH. The capture of free radicals R\* by crystallites is equivalent to the kinetic chain termination if these radicals remain in the crystallites or recombine in them. It was shown (Shlyapnikov Yu.A., 1986) that if these radicals are only kept inside the crystallites for a certain time, this is equivalent to chain termination if the reaction is self – accelerated.

The given section is devoted to regularities of thermal oxidation and to structural reconstructions in the course of oxidation of model heterogeneous systems (Shibryaeva L.S., 2010). The change of destruction rate of PP chains in the presence of modifier may be explained by the change of mechanism of polymer oxidation. Increase of segment mobility of chain leads to increase of contribution of intermolecular transfer of kinetic chains of oxidation. As a result of this kinetic chains of oxidation become shorter and the number of breakages in macromolecules is increased. But in the case of destruction process acceleration at the stage of kinetic chains continuation at the expense of prevailing of intermolecular transfer in composition of hydroxyl containing products the single OH-groups will prevail. However analysis of products composition did not reveal prevailing of single OH-groups over block ones. Increase of chains mobility is observed not only in the case of PP with compatible additives, but also for uncompatible, nevertheless the rate of PP oxidation in its presence is reduced. The most probable reason of oxidation process acceleration in samples of PP with compatible additives, of the rise of PP chain destruction rate is joint oxidation (co-oxidation) of polymer and additives. There are two fundamental hypotheses concerning the mechanism of these reactions which can be derived from the present experimental knowledge of structure and reactivity of macroradicals. (1) Hypothesis of physical migration by which the reactions of reactants are controlled either by mobility of the chains or their parts (segments) with fixed free valence or by diffusion of the low-molecular products of macroradical decomposition, e.i. the so-called radical fragments. (2) Hypothesis of chemical migration by which the reactions of reactants are controlled by various reactions of macroradicals of low-molecular fragments.

The samples of Isotactic PP non-inhibited powder of polymerizate was purified by standard

The kinetics of oxidation of isotactic polypropylene was investigated in circulating apparatus with freeze-volatile products of oxidation at the temperature of liquid nitrogen. When the film thickness is less than 60 microns maximum rate of oxidation of the sample is proportional to its thickness. Consequently, at a thickness of less than 60 microns ( l<60 mcm) kinetic regime is realized, i.e. diffusion of oxygen is a rapid process and does not affect the rate of oxidation. On the contrary, for l > 200 microns oxidation occurs in the diffusion regime and the maximum speed calculated for 1 cm2 the surface is practically

**4. Isotactic pp, modified by oil**

**5. Experimental part**

**5.1 The methods of investigation**

**5.1.1 Kinetics of oxidation**

independent of the thickness.

technique.

**1. Introduction**

Prévost-Bouré et al., 2010, Szanser, 2000).

and invertebrate remains into the litter.

**2.1 Study site and experimental design**

**2. Materials and methods**

**6**

M. Szanser

*Poland*

*Polish Academy of Sciences,*

*Centre for Ecological Research, Łomianki,*

**Decomposition of Artificial**

**Litter Made of Polypropylene**

Environmental pollution with plastic, especially polyolefins increased during the last decades. Due to recalcitrance of these substrates the studies on procedures speeding up the degradation and biological decomposition of polyolefins are carried intensively. The data concerning polypropylene (PP) disappearance rate are scarce comparing to the decomposition of polyethylene (PE) products (Ammala et al., 2011, Arutchelvi et al., 2008, Eubeler et al., 2010). It has been shown that pretreated PP disappear more quickly than poly(propylene-co-ethylene) (CPP) and PE polymers (Arutchelvi et al., 2008, Meligi et al., 1995, Sivan, 2011). However slower degradability of PP comparing to other plastics has been reported (Yang et al., 2005). It is known that UV radiation and weathering processes can speed up biodegradation processes of plastics in later stages of disappearance. Some studies of the PP and PE biodegradation showed that microorganisms, both bacteria and fungi, colonised the pre-treated or composted plastic substrata to greater extent comparing to control treatments (Ammala et al., 2011, Arutchelvi et al., 2008, Eubeler et al., 2010, Grunz et al., 1999, Meligi et al., 1995). There is a little information about the biodegradability of PP in the natural environment and impact of fresh organic matter input on PP decomposition. It seems that the natural input of nitrogen-rich organic matter both of plant and invertebrate origin might accelerate microbial activity and in consequence speed up the decomposition processes of recalcitrant materials (Crow et al., 2009, Dekker et al., 2005, Griffiths, 1994

The aim of the study was to compare the decomposition rate of the PP and natural plant litter (NPL). The hypothesis was that the decomposition of artificial litter made of PP will proceed effectively as in the case of natural litters due to additive effects of the input of plant

The study was carried out in a permanent meadow of the type Arrhenatheretalia situated in the buffer zone of Kampinos National Park (52°15'30" N and 20°17' E, east-central Poland).

№ 5. PP.1167-1170.; (1982) "The loss of peroxide macroradicals in the crystalline phase of isotactic polypropylene". *Vysokomolek. Soedin*.V. 24. № 6. PP.1241-1246.

## **Decomposition of Artificial Litter Made of Polypropylene**

## M. Szanser

*Polish Academy of Sciences, Centre for Ecological Research, Łomianki, Poland*

## **1. Introduction**

86 Polypropylene

Shibryaeva L.S., Shatalova O.V., Solovova J.V. and al. (2010). "Features of thermal

Shlyapnikov, Yu.A., Kiryushkin S.G Marin. A.P.1986. *Antioxidantive stabilization of*

Shlyapnikov Yu.A. (1989) "Specific features of polymer oxidation" *Makromol. Chem.,*

P.35-55. ISBN -13: 978-90-6764-451-8; ISBN-10:90-6764-451-X.

*himicheskoy technologii*. V.44. № 4. P. 454-466.

*Macromol. Symp.* V.27. № 1. PP. 121-138.

*polymers*. Moscow. Chemistry.P. 254. (In Russian).

№ 5. PP.1167-1170.; (1982) "The loss of peroxide macroradicals in the crystalline phase of isotactic polypropylene". *Vysokomolek. Soedin*.V. 24. № 6. PP.1241-1246. Shibryaeva L.S., Shatalova O.V., Krivandin A.V. and al. (2003) "Structure Effects in the Oxidation of Isotactic Polypropylene" *Vysokomolek. Soedin*. 45 А. № 3.PP.421-435. Shibryaeva L.S.,Popov A.A., Zaikov G.E. (2006). *Thermal Oxidation of Polymer Blends*.

Ch.2"Structure effects in thermal oxidation of polyolefines".Leiden, Boston: VSP

oxidation of polypropylene modified with paraffin oil." *Theoretical osnovy*

Environmental pollution with plastic, especially polyolefins increased during the last decades. Due to recalcitrance of these substrates the studies on procedures speeding up the degradation and biological decomposition of polyolefins are carried intensively. The data concerning polypropylene (PP) disappearance rate are scarce comparing to the decomposition of polyethylene (PE) products (Ammala et al., 2011, Arutchelvi et al., 2008, Eubeler et al., 2010). It has been shown that pretreated PP disappear more quickly than poly(propylene-co-ethylene) (CPP) and PE polymers (Arutchelvi et al., 2008, Meligi et al., 1995, Sivan, 2011). However slower degradability of PP comparing to other plastics has been reported (Yang et al., 2005). It is known that UV radiation and weathering processes can speed up biodegradation processes of plastics in later stages of disappearance. Some studies of the PP and PE biodegradation showed that microorganisms, both bacteria and fungi, colonised the pre-treated or composted plastic substrata to greater extent comparing to control treatments (Ammala et al., 2011, Arutchelvi et al., 2008, Eubeler et al., 2010, Grunz et al., 1999, Meligi et al., 1995). There is a little information about the biodegradability of PP in the natural environment and impact of fresh organic matter input on PP decomposition. It seems that the natural input of nitrogen-rich organic matter both of plant and invertebrate origin might accelerate microbial activity and in consequence speed up the decomposition processes of recalcitrant materials (Crow et al., 2009, Dekker et al., 2005, Griffiths, 1994 Prévost-Bouré et al., 2010, Szanser, 2000).

The aim of the study was to compare the decomposition rate of the PP and natural plant litter (NPL). The hypothesis was that the decomposition of artificial litter made of PP will proceed effectively as in the case of natural litters due to additive effects of the input of plant and invertebrate remains into the litter.

## **2. Materials and methods**

### **2.1 Study site and experimental design**

The study was carried out in a permanent meadow of the type Arrhenatheretalia situated in the buffer zone of Kampinos National Park (52°15'30" N and 20°17' E, east-central Poland).

Decomposition of Artificial Litter Made of Polypropylene 89

distribution. Only total data for PP litter and remnants had normal distribution. Differences in mass of litter and remnants between treatments were assessed using non-parametric Wilcoxon Sum-of-Ranks (Mann-Whitney) test for comparing two unmatched samples. The regression between masses of remaining litter and remnants were assessed using the Kendall tau Rank Correlation test and linear regression analysis for natural and

The highest values of the NPL mass loss were recorded in the initial period, while the loss of PP litter was the slowest (Table 1). In the first 6 months following exposure, the loss of dry weight mass of litter reached 59.8 and 28.1% respectively for NPL and PP treatments (Table 1). Later, further losses of litter, during over two years period, were observed being 70.53 and 72.45% for NPL and PP treatments respectively. In the final period, i.e., between the 26th and 30th months of the experiment, the increases of both types litter mass were larger than its losses. This could be explained by the organic matter (of plant and animal origin) input and colonisation of the litter by invertebrates and microorganisms during long period

(7.22)

(9.98)

(14.23)

Differences between NPL(data taken together) and PP treatments in the litter decomposition rate resulted from litter origin. Remaining mass of artificial litter (PP) was higher in every sampling time by 43.9%, 27.4% and 22.8% comparing to natural (NPL) ones respectively after 6, 26 and 30 months of the experiment but the differences were significant only for the first sampling occasion (Table 1). Interestingly slight increase of litter mass occurred in PP

Table 1. Mass (g dry weight m-2) of remaining and percent (%) of initial mass of exposed natural plant (NPL) and polypropylene (PP) litter during the course of the experiment. Significance of differences between treatments are assessed by non-parametric Wilcoxon Sumof-Ranks (Mann-Whitney) test. All data from five natural litter treatments (I: *Dactylis glomerata*; II: *Festuca rubra* and III: *Trifolium pratense*), IV: mixture of three species I, II and III; V: mixture of twelve species, IV and nine other meadow plants) were analyzed with the exception of 26th month where only data of treatments I and III were used. Standard errors in parentheses.

**Litter type** Significance of

treatments NPL PP

646.78 (24.69)

337.98 (28.61)

360.88 (58.91) differences between

n = 55, W = 502.5, p<=0.00000

n = 35, W = 106.5, p<=0.4229

n = 35, W = 111.5, p<=0.1573

polypropylene treatments, respectively.

**3. Results**

**3.1 Litter decomposition**

of the exposure (2.5 years).

6 g dry weight m-2 362.28

26 g dry weight m-2 265.26

30 g dry weight m-2 293.78

% 40.25 71.86

% 29.47 37.55

% 32.64 40.1

treatment similarly as in natural litter at the end of the experiment.

Months since beginning of the experiment

An experiment was conducted to compare the decomposition pattern of natural plant litters (NPL) and of artificial litter composed of natural not dyed PP agricultural string. The experimental meadow of an area of 190 x 10 m had 182 microplots ( 0.5 x 0.5m area and 0.15 m depth). Five natural and one artificial litter treatments in 32 and 22 plot replicates respectively according to RCB design were applied (Pearce, 1983). Eight litter containers per plot were placed. Natural litter was obtained from meadow plants, both grasses and weeds cut in August 2001 which had to simulate the input of decaying plants to soil. The same amount of PP and NPL (9 g dry wt.) irrespective of the number of plant species was exposed in modified litter containers. Experimental plots were filled with sand mixed with loam to the depth of 15 cm. Such type of simplified and uniform substrate, among them, enabled assessing the input of organic matter morphous particles in exposed litter and in underlying substrate.

Litter samples were mounted under stainless steel wires stuck into the substrate. In that way a more compact structure of exposed material which adhered to the substratum was obtained, providing fauna with better access to the litter without covering containers by a net on the top. NPL were either monospecific (I: *Dactylis glomerata*; II: *Festuca rubra* and III: *Trifolium pratense*) or were species mixtures (IV: mixture of three species I, II and III; V: mixture of twelve species, IV and nine other meadow plants). In the latter case, the following species were used: grasses: brome grass (*Bromus inermis*), meadow foxtail (*Alopecurus pratensis*), perennial ryegrass (*Lolium perenne*), oat grass (*Arrhenatherum elatius*), cocksfoot (*Dactylis glomerata*), and red fescue (*Festuca rubra*); and herbs: small plantain (*Plantago lanceolata*), common chicory (*Cichorium intybus*), red clover (*Trifolium pratense*), milfoil (*Achillea millefolium*), carrot (*Daucus carota*), and common silverweed (*Potentilla anserina*)*.*

#### **2.2 Sample collecting and processing**

The experiment started on 24-25 March 2002. Samples were taken on 27 September 2002, 11 May 2004, 9 September 2004, i.e., 6, 26, and 30 months after litter exposure.

Litter and soil samples were taken per 5-11 in every sampling occasion. Soil samples for assessments of plant and invertebrate organic matter input were taken to the depth of 1 cm with a soil corer 100 cm2 in area.

#### **2.3 Plant and invertebrate materials**

#### **2.3.1 Litter mass loss**

Litter mass loss was determined using the gravimetric method by drying at 65oC.

#### **2.3.2 Input of wind-borne plant matter and invertebrate remnants into litter and underlying substrate**

The input of the remnants of invertebrate origin (exuviae, cocoons, other remants) was assessed in the litter and soil layer 0-1 cm underneath the litter by hand-sorting and using the stereoscope microscopy.

#### **2.4 Statistical analysis**

Statistical analyses of results (one-way *ANOVA* and regression) were performed using Statistica 8.0. software (StatSoft, Inc. (2007). Natural litter and remnants' data had no normal distribution. Only total data for PP litter and remnants had normal distribution. Differences in mass of litter and remnants between treatments were assessed using non-parametric Wilcoxon Sum-of-Ranks (Mann-Whitney) test for comparing two unmatched samples. The regression between masses of remaining litter and remnants were assessed using the Kendall tau Rank Correlation test and linear regression analysis for natural and polypropylene treatments, respectively.

## **3. Results**

88 Polypropylene

An experiment was conducted to compare the decomposition pattern of natural plant litters (NPL) and of artificial litter composed of natural not dyed PP agricultural string. The experimental meadow of an area of 190 x 10 m had 182 microplots ( 0.5 x 0.5m area and 0.15 m depth). Five natural and one artificial litter treatments in 32 and 22 plot replicates respectively according to RCB design were applied (Pearce, 1983). Eight litter containers per plot were placed. Natural litter was obtained from meadow plants, both grasses and weeds cut in August 2001 which had to simulate the input of decaying plants to soil. The same amount of PP and NPL (9 g dry wt.) irrespective of the number of plant species was exposed in modified litter containers. Experimental plots were filled with sand mixed with loam to the depth of 15 cm. Such type of simplified and uniform substrate, among them, enabled assessing the input of organic matter morphous particles in exposed litter and in underlying substrate. Litter samples were mounted under stainless steel wires stuck into the substrate. In that way a more compact structure of exposed material which adhered to the substratum was obtained, providing fauna with better access to the litter without covering containers by a net on the top. NPL were either monospecific (I: *Dactylis glomerata*; II: *Festuca rubra* and III: *Trifolium pratense*) or were species mixtures (IV: mixture of three species I, II and III; V: mixture of twelve species, IV and nine other meadow plants). In the latter case, the following species were used: grasses: brome grass (*Bromus inermis*), meadow foxtail (*Alopecurus pratensis*), perennial ryegrass (*Lolium perenne*), oat grass (*Arrhenatherum elatius*), cocksfoot (*Dactylis glomerata*), and red fescue (*Festuca rubra*); and herbs: small plantain (*Plantago lanceolata*), common chicory (*Cichorium intybus*), red clover (*Trifolium pratense*), milfoil (*Achillea*

*millefolium*), carrot (*Daucus carota*), and common silverweed (*Potentilla anserina*)*.*

May 2004, 9 September 2004, i.e., 6, 26, and 30 months after litter exposure.

Litter mass loss was determined using the gravimetric method by drying at 65oC.

**2.3.2 Input of wind-borne plant matter and invertebrate remnants into litter and**

The input of the remnants of invertebrate origin (exuviae, cocoons, other remants) was assessed in the litter and soil layer 0-1 cm underneath the litter by hand-sorting and using

Statistical analyses of results (one-way *ANOVA* and regression) were performed using Statistica 8.0. software (StatSoft, Inc. (2007). Natural litter and remnants' data had no normal

The experiment started on 24-25 March 2002. Samples were taken on 27 September 2002, 11

Litter and soil samples were taken per 5-11 in every sampling occasion. Soil samples for assessments of plant and invertebrate organic matter input were taken to the depth of 1 cm

**2.2 Sample collecting and processing**

with a soil corer 100 cm2 in area.

**2.3.1 Litter mass loss**

**underlying substrate**

the stereoscope microscopy.

**2.4 Statistical analysis**

**2.3 Plant and invertebrate materials**

### **3.1 Litter decomposition**

The highest values of the NPL mass loss were recorded in the initial period, while the loss of PP litter was the slowest (Table 1). In the first 6 months following exposure, the loss of dry weight mass of litter reached 59.8 and 28.1% respectively for NPL and PP treatments (Table 1). Later, further losses of litter, during over two years period, were observed being 70.53 and 72.45% for NPL and PP treatments respectively. In the final period, i.e., between the 26th and 30th months of the experiment, the increases of both types litter mass were larger than its losses. This could be explained by the organic matter (of plant and animal origin) input and colonisation of the litter by invertebrates and microorganisms during long period of the exposure (2.5 years).

Table 1. Mass (g dry weight m-2) of remaining and percent (%) of initial mass of exposed natural plant (NPL) and polypropylene (PP) litter during the course of the experiment. Significance of differences between treatments are assessed by non-parametric Wilcoxon Sumof-Ranks (Mann-Whitney) test. All data from five natural litter treatments (I: *Dactylis glomerata*; II: *Festuca rubra* and III: *Trifolium pratense*), IV: mixture of three species I, II and III; V: mixture of twelve species, IV and nine other meadow plants) were analyzed with the exception of 26th month where only data of treatments I and III were used. Standard errors in parentheses.

Differences between NPL(data taken together) and PP treatments in the litter decomposition rate resulted from litter origin. Remaining mass of artificial litter (PP) was higher in every sampling time by 43.9%, 27.4% and 22.8% comparing to natural (NPL) ones respectively after 6, 26 and 30 months of the experiment but the differences were significant only for the first sampling occasion (Table 1). Interestingly slight increase of litter mass occurred in PP treatment similarly as in natural litter at the end of the experiment.

Decomposition of Artificial Litter Made of Polypropylene 91

Summarized data of both plant and invertebrate material revealed that significantly higher was the mass of new organic material in PP comparing to natural treatments after 6 months of the experiment (Table 4). Later the differences between treatments were not significant. The values of total organic matter input were 45.4 and 40.8 g dry wt. m-2 for natural and PP

The negative correlations between mass of remaining litter and input of both types of remnants were found for NPL (r = -0.456, Z = -7.230, *P* <0.00000, n = 115) and PP (r = -0.415,

> Litter type Significance of differences NPL PP between treatments

> > n = 60, W = 305, p <= 0.9921

n = 24, W = 69, p <=0.7139

n = 51, W = 138, p <= 0.6089

11.8 (2.08)

14.73 (2.66)

40.78 (15.66)

r2 = 0.172, *F* = 3.743, *P* <0.0689, n = 20) treatments taking the entire study period data.

(0.42)

(9.32)

(5.73)

Table 4. Sum of plant and invertebrate remnants (g dry weight m-2) in NPL and PP litter during the course of the experiment. Differences between treatments are assessed by nonparametric Wilcoxon Sum-of-Ranks (Mann-Whitney) test. All data from five natural litter treatments (I: *Dactylis glomerata*; II: *Festuca rubra* and III: *Trifolium pratense*), IV: mixture of three species I, II and III; V: mixture of twelve species, IV and nine other meadow plants) were analyzed with the exception of 26th month where only data of treatments I and III were

The meteorological data indicated that climatic conditions in the study period were unfavourable for soil organisms (Szanser et al., 2011). Artificial litter (PP) was drier comparing to natural litters (NPL) and retained a maximum of 5% moisture even during rainfall, while its underlying substrate was similarly wet as that under natural litters (Szanser et al., 2011). Lower mass loss of PP comparing to NPL was coincided with significantly lower numbers of fungi and bacteria in the PP litter and its respiration by 3.4, 44.8 and 61.4 times respectively comparing to natural treatments (Górska unpubl., Szanser et al., 2011). Interestingly number of fungi was the parameter the least differentiating between PP and other treatments. It may signify that the decomposition of PP was of fungal nature. Nevertheless it was found that almost 60 and 70% of the exposed PP and natural litters degraded by 26th month of the experiment. It seems that degradation of PP was quite effective as far as there were no significant differences between applied treatments at the end of the experiment. Thirty months after litter exposure, the input of wind-borne plant material was similar in both treatments. Considerably smaller was the mass of invertebrate origin (exuviae, cocoons, other remnants in both treatments. Similar input of invertebrate organic matter found in later stages of the experiment is corroborated by the lack of significant differences between PP and natural litters in invertebrate macrofauna penetration (Kajak, Szanser, unpubl.). Similar values of the input of plant and invertebrate remnants into natural litter and underlying substrate were found in other agricultural and meadow environments (Szanser,

treatments respectively at the end of the experiment.

<sup>6</sup>5.19

<sup>26</sup>37.62

<sup>30</sup>45.40

Months since beginning of the experiment

used. Standard errors in parentheses.

**4. Discussion**

#### **3.2 Input of plant and invertebrate remnants**

There was considerably large input of wind-borne plant material into exposed litter. It was still low after 6 months of the experiment and was particularly high by the 26th month. There was further slight increase of plant remnants input between 26th and 30th month of the experiment. PP litter had significantly higher input of wind-borne plant matter comparing to NPL only after 6 months of the experiment (Table 2). Later the differences between treatments were not significant. The values of wind-borne plant materials were 43.4 and 39.6 g dry wt. m-2 for NPL and PP treatments respectively at the end of the experiment. This input constituted 4.82 and 4.4 % of the initial mass of natural and artificial litter, respectively. Much smaller was the mass of invertebrate origin (exuviae, cocoons, other remnants) found in both treatments but the differences between treatments were not significant (Table 3). The mass of invertebrate remnants amounted to 2.0 and 1.2 g dry wt. m-2 for NPL and PP treatments respectively at the end of the experiment.

Table 2. Mass of wind-borne plant remnants (g dry weight m-2) in natural plant (NPL) and polypropylene (PP) litter during the course of the experiment. Differences between treatments are assessed by non-parametric Wilcoxon Sum-of-Ranks (Mann-Whitney) test. All data from five natural litter treatments (I: *Dactylis glomerata*; II: *Festuca rubra* and III: *Trifolium pratense*), IV: mixture of three species I, II and III; V: mixture of twelve species, IV and nine other meadow plants) were analyzed with the exception of 26th month where only data of treatments I and III were used. Standard errors in parentheses.

Table 3. Mass of invertebrate remnants (g dry weight m-2) in NPL and PP litter during the course of the experiment. Differences between treatments are assessed by non-parametric Wilcoxon Sum-of-Ranks (Mann-Whitney) test. All data from five natural litter treatments (I: *Dactylis glomerata*; II: *Festuca rubra* and III: *Trifolium pratense*), IV: mixture of three species I, II and III; V: mixture of twelve species, IV and nine other meadow plants) were analyzed with the exception of 26th month where only data of treatments I and III were used. Standard errors in parentheses.

Summarized data of both plant and invertebrate material revealed that significantly higher was the mass of new organic material in PP comparing to natural treatments after 6 months of the experiment (Table 4). Later the differences between treatments were not significant. The values of total organic matter input were 45.4 and 40.8 g dry wt. m-2 for natural and PP treatments respectively at the end of the experiment.

The negative correlations between mass of remaining litter and input of both types of remnants were found for NPL (r = -0.456, Z = -7.230, *P* <0.00000, n = 115) and PP (r = -0.415, r2 = 0.172, *F* = 3.743, *P* <0.0689, n = 20) treatments taking the entire study period data.

Table 4. Sum of plant and invertebrate remnants (g dry weight m-2) in NPL and PP litter during the course of the experiment. Differences between treatments are assessed by nonparametric Wilcoxon Sum-of-Ranks (Mann-Whitney) test. All data from five natural litter treatments (I: *Dactylis glomerata*; II: *Festuca rubra* and III: *Trifolium pratense*), IV: mixture of three species I, II and III; V: mixture of twelve species, IV and nine other meadow plants) were analyzed with the exception of 26th month where only data of treatments I and III were used. Standard errors in parentheses.

## **4. Discussion**

90 Polypropylene

There was considerably large input of wind-borne plant material into exposed litter. It was still low after 6 months of the experiment and was particularly high by the 26th month. There was further slight increase of plant remnants input between 26th and 30th month of the experiment. PP litter had significantly higher input of wind-borne plant matter comparing to NPL only after 6 months of the experiment (Table 2). Later the differences between treatments were not significant. The values of wind-borne plant materials were 43.4 and 39.6 g dry wt. m-2 for NPL and PP treatments respectively at the end of the experiment. This input constituted 4.82 and 4.4 % of the initial mass of natural and artificial litter, respectively. Much smaller was the mass of invertebrate origin (exuviae, cocoons, other remnants) found in both treatments but the differences between treatments were not significant (Table 3). The mass of invertebrate remnants amounted to 2.0 and 1.2 g dry wt.

Litter type Significance of differences

Litter type Significance of differences

NPL PP between treatments

n = 60, W = 305, p <= 0.9921

n = 24, W = 69, p <=0.7139

n = 51, W = 138, p <= 0.6089

n = 60, W = 305, p <= 0.9921

n = 24, W = 75, p <= 0.9734

n = 51, , W = 156, p <= 0.9883

NPL PP between treatments

9.31 (1.99)

14.14 (2.67)

39.60 (15.52)

2.49 (0.50)

0.58 (0.33)

1.17 (0.33)

m-2 for NPL and PP treatments respectively at the end of the experiment.

(0.37)

(9.26)

(5.72)

(0.23)

(0.33)

(0.36)

Table 3. Mass of invertebrate remnants (g dry weight m-2) in NPL and PP litter during the course of the experiment. Differences between treatments are assessed by non-parametric Wilcoxon Sum-of-Ranks (Mann-Whitney) test. All data from five natural litter treatments (I: *Dactylis glomerata*; II: *Festuca rubra* and III: *Trifolium pratense*), IV: mixture of three species I, II and III; V: mixture of twelve species, IV and nine other meadow plants) were analyzed with the exception of 26th month where only data of treatments I and III were used. Standard

Table 2. Mass of wind-borne plant remnants (g dry weight m-2) in natural plant (NPL) and polypropylene (PP) litter during the course of the experiment. Differences between treatments are assessed by non-parametric Wilcoxon Sum-of-Ranks (Mann-Whitney) test. All data from five natural litter treatments (I: *Dactylis glomerata*; II: *Festuca rubra* and III: *Trifolium pratense*), IV: mixture of three species I, II and III; V: mixture of twelve species, IV and nine other meadow plants) were analyzed with the exception of 26th month where only data of

<sup>6</sup>3.71

<sup>26</sup>36.77

<sup>30</sup>43.40

treatments I and III were used. Standard errors in parentheses.

<sup>6</sup>1.48

<sup>26</sup>0.85

<sup>30</sup>2.00

**3.2 Input of plant and invertebrate remnants**

Months since beginning of the experiment

Months since beginning of the experiment

errors in parentheses.

The meteorological data indicated that climatic conditions in the study period were unfavourable for soil organisms (Szanser et al., 2011). Artificial litter (PP) was drier comparing to natural litters (NPL) and retained a maximum of 5% moisture even during rainfall, while its underlying substrate was similarly wet as that under natural litters (Szanser et al., 2011). Lower mass loss of PP comparing to NPL was coincided with significantly lower numbers of fungi and bacteria in the PP litter and its respiration by 3.4, 44.8 and 61.4 times respectively comparing to natural treatments (Górska unpubl., Szanser et al., 2011). Interestingly number of fungi was the parameter the least differentiating between PP and other treatments. It may signify that the decomposition of PP was of fungal nature. Nevertheless it was found that almost 60 and 70% of the exposed PP and natural litters degraded by 26th month of the experiment. It seems that degradation of PP was quite effective as far as there were no significant differences between applied treatments at the end of the experiment. Thirty months after litter exposure, the input of wind-borne plant material was similar in both treatments. Considerably smaller was the mass of invertebrate origin (exuviae, cocoons, other remnants in both treatments. Similar input of invertebrate organic matter found in later stages of the experiment is corroborated by the lack of significant differences between PP and natural litters in invertebrate macrofauna penetration (Kajak, Szanser, unpubl.). Similar values of the input of plant and invertebrate remnants into natural litter and underlying substrate were found in other agricultural and meadow environments (Szanser,

Decomposition of Artificial Litter Made of Polypropylene 93

Chemidlin Prévost-Bouré, N., Soudani, K., Damesin, C., Berveiller, D., Lata, J.-C., and

Crow, S. E., Lajtha, K., Bowden, R. D., Yano, Y., Brant, J. B., Caldwell, B. A., and Sulzman, E.

Dekker, S. C., Scheu, S., Schröter D., Setälä, H., Szanser, M. and Traas, T. P. (2005). Towards

Eubeler, J. P., Bernhard, M., and Knepper, T. P. (2010). Environmental biodegradation of

Griffiths B. S. 1994 - Microbial-feeding nematodes and protozoa in soil: Their effects on

Kram K.J. (2005). Bulk precipitation and aerosol-gaseous input of elements in the forested

Meligi, G., Yoshii, F., Sasaki. T., Makuuchi, K., Rabie, A. M. and Nishimoto, S-I., 1995.

Grunz, A., Dayss, E., and Leps, G. (1999). Biomass covering of plastics substrates depending

Pearce, S.C. (1983). *The Agricultural Field Experiment: a Statistical Examination of Theory and*

Sivan, A. (2011). New perspectives in plastic biodegradation. *Current Opinion in Biotechnology* , Vol. 22, No. 3, (June 2011), pp. 422-426, ISSN: 0958-1669. Stachurski, A., and Zimka, J. R. (2000). Atmospheric input of elements to forest ecosystems:

Szanser M. 2000 - Effect of macroarthropods patrolling soil surface on decomposition rate of

(September 2010), pp. 26-34, ISSN: 0929-1393.

(October 2009), pp. 2224-2232 ISSN: 0378-1127.

No. 2, pp. 261–268, (June 2005), ISSN 1505-2249.

1999), pp. 831-835, ISSN: 0257-8972.

No. 2, (No information 1995), pp 323-327, ISSN: 0141-3910.

STATISTICA (data analysis software system), version 8.0. www.statsoft.com).

48, No. 4, (October 2000), pp. 283-297, ISSN 1505-2249.

9936.

079X.

0471105112.

7491.

pp. 258-269 Elsevier, Amsterdam, ISBN: 978-0-12-088458-2.

Dufrêne, E. (2010). Increase in aboveground fresh litter quantity over-stimulates soil respiration in a temperate deciduous forest. *Applied Soil Ecology*, Vol. 46, No. 1,

W. (2009). Increased coniferous needle inputs accelerate decomposition of soil carbon in an old-growth forest. *Forest Ecology and Management*, Vol. 258, No 10,

a new generation of dynamical soil decomposer food web models. Pages 590 *in* P. C. De Ruiter, V. Wolters, and J. C. Moore, editors. *Dynamic Food Webs -multispecies assemblages, ecosystem development and environmental change*, (No information 2006)

synthetic polymers II. Biodegradation of different polymer groups. *TrAC Trends in Analytical Chemistry* , Vol. 29,No 1, (January 2010), pp. 84-100, ISSN: 0165-

microbial activity and nitrogen mineralization in decomposition hotspots and the rhizosphere - *Plant and Soil*, Vol. 164, No 1, (January 1994), pp. 25-33, ISSN: 0032-

area of coastal region (Pomerania, north Poland). *Polish Journal of Ecology*, Vol. 53,

Comparison of the degradability of irradiated polypropylene and poly(propyleneco-ethylene) in the natural environment, *Polymer Degradation and Stability*, Vol. 49,

on plasma treatment. *Surface and Coatings Technology* Vol. 116-119, (September

*Practice*. New York: John Wiley & Sons, (No information 1983), pp. 335, ISBN-10:

a method of estimation using artificial foliage placed above rain collectors. *Environmental Pollution*, Vol. 110, No. 2, (November 2000), pp. 345-356, ISSN: 0269-

grass litter (*Dactylis glomerata*) in a field experiment – Polish Journal of Ecology Vol.

2003, Szanser, unpubl.). It seems that input of organic matter into PP had some effect on its biodegradation. It should be pointed out that the absorption of different ions (Na+, N-NH4+, K+, Mg 2+, Cl–, N-NO3**–**, S-SO4 2–) by exposed PP from aerosol-gaseous input, although not measured in this study, can have additional impact on speeding up PP biodegradation. It was found that absorption of elements by polymers used as "artificial leaves" can be quite high and increase with surface area of the exposed plastic (Kram, 2005, Stachurski & Zimka 2000). It seems that the aerosol-gaseous input of elements together with input of new organic matter and further development of microorganisms in fibrous PP resulted in efficient decomposition of the PP. Observed slight increase of polymer mass towards the end of the experiment simultaneously as in natural litter can be explained by the organic matter input and development of microbial communities. The mechanisms involved in PP biodegradation are corroborated by data obtained from experimental underlying substrates. There were no significant differences in microbial activity (soil respiration, microbial biomass and numbers of bacteria and fungi) between PP and NPL treatments in underlying substrate during the third year of the experiment (Górska, Szanser, unpubl.). On the opposite algal biomass and production were by 36% and 39.7% respectively higher under PP comparing to NPL treatments for entire study time (Sieminiak, unpubl.). The increase of carbon content under the PP was higher by 47% than in natural treatments at the end of the experiment (Kusińska & Szanser unpubl.). It should be pointed out that the paper presents results obtained from long-time field experiment while most of the research on degrading the polymers are short time studies.

### **5. Conclusions**

In general, the results suggest that (1) the long term decomposition of artificial litter (PP) proceeded efficiently but was still quite low comparing to natural treatments; (2) the input of plant and invertebrate remains into the PP can be considerably large and may have an additive effect on its decomposition; (3) it seems that longtime decomposition of natural PP may be quite effective comparing to plant litters and (4) the presence of PP did not inhibit severely soil biota activity and organic matter accumulation in soil during the experiment.

#### **6. Acknowledgments**

This research was supported by a grant from the Polish State Committee for Scientific Research, project P04 F 03820.

#### **7. References**

2003, Szanser, unpubl.). It seems that input of organic matter into PP had some effect on its biodegradation. It should be pointed out that the absorption of different ions (Na+, N-NH4+,

measured in this study, can have additional impact on speeding up PP biodegradation. It was found that absorption of elements by polymers used as "artificial leaves" can be quite high and increase with surface area of the exposed plastic (Kram, 2005, Stachurski & Zimka 2000). It seems that the aerosol-gaseous input of elements together with input of new organic matter and further development of microorganisms in fibrous PP resulted in efficient decomposition of the PP. Observed slight increase of polymer mass towards the end of the experiment simultaneously as in natural litter can be explained by the organic matter input and development of microbial communities. The mechanisms involved in PP biodegradation are corroborated by data obtained from experimental underlying substrates. There were no significant differences in microbial activity (soil respiration, microbial biomass and numbers of bacteria and fungi) between PP and NPL treatments in underlying substrate during the third year of the experiment (Górska, Szanser, unpubl.). On the opposite algal biomass and production were by 36% and 39.7% respectively higher under PP comparing to NPL treatments for entire study time (Sieminiak, unpubl.). The increase of carbon content under the PP was higher by 47% than in natural treatments at the end of the experiment (Kusińska & Szanser unpubl.). It should be pointed out that the paper presents results obtained from long-time field experiment while most of the research on degrading

In general, the results suggest that (1) the long term decomposition of artificial litter (PP) proceeded efficiently but was still quite low comparing to natural treatments; (2) the input of plant and invertebrate remains into the PP can be considerably large and may have an additive effect on its decomposition; (3) it seems that longtime decomposition of natural PP may be quite effective comparing to plant litters and (4) the presence of PP did not inhibit severely soil biota activity and organic matter accumulation in soil during the

This research was supported by a grant from the Polish State Committee for Scientific

Ammala, A., Bateman, S., Dean, K., Petinakis, E., Sangwan, P., Wong, S., Yuan, Q., Yu, L.,

Arutchelvi, J., Sudhakar, M., Arkatkar, A., Doble, M., Bhaduri, S., and Uppara, P. V. (2008).

Vol. 7, No. 1, (January 2008), pp. 9-22, ISSN: 0972-5849.

Patrick, C., and Leong, K. H. (2011). An overview of degradable and biodegradable polyolefins. *Progress in Polymer Science* Vol. 36, No. 8, (August 2011), pp. 1015-1049,

Biodegradation of polyethylene and polypropylene. *Indian Journal of Biotechnology*,

2–) by exposed PP from aerosol-gaseous input, although not

K+, Mg 2+, Cl–, N-NO3

the polymers are short time studies.

**5. Conclusions**

experiment.

**7. References**

**6. Acknowledgments**

Research, project P04 F 03820.

ISSN: 0079-6700.

**–**, S-SO4

**7**

*Brazil*

*1Embrapa Vegetables, 2Embrapa Instrumentation*

**Modified Atmosphere Packaging**

Leonora M. Mattos1, Celso L. Moretti1 and Marcos D. Ferreira2

Packaging perishable plant products is one of the more important steps in the long and complicated journey from grower to consumer. Millions of different types of packages are used for produce around the world and the number continues to increase as the industry introduces new packaging materials and concepts. Packing and packaging materials contribute a significant cost to the produce industry; therefore it is important that packers, shippers, buyers, and consumers have a clear understanding of the wide range of packaging options available (Boyette et al., 1996). This fact chapter describes some of the many types of packaging materials, including their functions, uses, and limitations. Within packaging plastics for plant products, if commodity and film permeability characteristics are properly matched, an appropriate atmosphere can evolve passively through consumption of O2 and production of CO2 during respiration (Mir & Beaudry, 2002). Gas exchange and respiration rate through the package material are the processes involved in creating a modied atmosphere inside a package that will extend shelf life of fresh fruits and vegetables. The major methods for measuring respiration rates, along with their advantages and limitations are discussed. Modified atmosphere technologies have great potential in a wide range of applications in plant products. The usual methods of respiration rate determination can be the static system, the owing system and the permeable system (Fonseca et al., 2002). The respiration rate of fresh produce can be expressed as O2 consumption rate and/or CO2 production rate. Factors affecting the respiration rate and respiratory quotient are outlined, stressing the importance of temperature, O2 and CO2 concentrations, and storage time (Kader et al., 1989). Modified atmosphere packaging should always be considered as a supplement to proper temperature and relative humidity management. The differences between beneficial and harmful concentrations of oxygen and carbon dioxide for each kind of produce are relatively small, so great care must be taken when using these technologies. Temperature has been identied as the most important external factor inuencing respiration (Tano et al., 2007). The internal factors affecting respiration are the type and maturity stage of the commodity. Vegetables include a great diversity of plant organs such as fruits, roots, tubers, seeds, bulbs, sprouts, leaves and stems that have different metabolic activities and consequently different respiration rates. Different varieties of the same product exhibit specific respiration rates. The success of modied atmosphere packaging greatly depends on the accuracy of the predictive respiration rate (Kader, 2002). The main objective of this chapter is to present different packaging materials using modified atmosphere for perishable plant products, focusing

**1. Introduction**

**for Perishable Plant Products**

## **Modified Atmosphere Packaging for Perishable Plant Products**

Leonora M. Mattos1, Celso L. Moretti1 and Marcos D. Ferreira2 *1Embrapa Vegetables,*

*2Embrapa Instrumentation Brazil*

#### **1. Introduction**

94 Polypropylene

Szanser, M. 2003 - The effect of shelterbelts on litter decomposition and fauna of adjacent

Szanser, M., Ilieva-Makulec, K., Kajak, A., Kusińska, A., Kisiel, M., Olejniczak, I., Russel, S.,

*Biochemistry*, Vol. 43, No. 1, (January 2011), pp. 9-19, ISSN: 0038-0717. Yang, H.-S., Yoon, J.-S., and Kim, M.-N. (2005). Dependence of biodegradability of plastics in

No. 1, (December 2004), pp. 131-135 ISSN: 0141-3910.

2003), pp.309-321, ISSN 1505-2249.

fields: In situ experiment - Polish Journal of Ecology, Vol.51, No.3, (September

Sieminiak, D., Wojewoda, D. (2011). Impact of litter species diversity on decomposition processes and communities of soil organisms - *Soil Biology and*

compost on the shape of specimens. Polymer Degradation and Stability, Vol. 87,

Packaging perishable plant products is one of the more important steps in the long and complicated journey from grower to consumer. Millions of different types of packages are used for produce around the world and the number continues to increase as the industry introduces new packaging materials and concepts. Packing and packaging materials contribute a significant cost to the produce industry; therefore it is important that packers, shippers, buyers, and consumers have a clear understanding of the wide range of packaging options available (Boyette et al., 1996). This fact chapter describes some of the many types of packaging materials, including their functions, uses, and limitations. Within packaging plastics for plant products, if commodity and film permeability characteristics are properly matched, an appropriate atmosphere can evolve passively through consumption of O2 and production of CO2 during respiration (Mir & Beaudry, 2002). Gas exchange and respiration rate through the package material are the processes involved in creating a modied atmosphere inside a package that will extend shelf life of fresh fruits and vegetables. The major methods for measuring respiration rates, along with their advantages and limitations are discussed. Modified atmosphere technologies have great potential in a wide range of applications in plant products. The usual methods of respiration rate determination can be the static system, the owing system and the permeable system (Fonseca et al., 2002). The respiration rate of fresh produce can be expressed as O2 consumption rate and/or CO2 production rate. Factors affecting the respiration rate and respiratory quotient are outlined, stressing the importance of temperature, O2 and CO2 concentrations, and storage time (Kader et al., 1989). Modified atmosphere packaging should always be considered as a supplement to proper temperature and relative humidity management. The differences between beneficial and harmful concentrations of oxygen and carbon dioxide for each kind of produce are relatively small, so great care must be taken when using these technologies. Temperature has been identied as the most important external factor inuencing respiration (Tano et al., 2007). The internal factors affecting respiration are the type and maturity stage of the commodity. Vegetables include a great diversity of plant organs such as fruits, roots, tubers, seeds, bulbs, sprouts, leaves and stems that have different metabolic activities and consequently different respiration rates. Different varieties of the same product exhibit specific respiration rates. The success of modied atmosphere packaging greatly depends on the accuracy of the predictive respiration rate (Kader, 2002). The main objective of this chapter is to present different packaging materials using modified atmosphere for perishable plant products, focusing

Modified Atmosphere Packaging for Perishable Plant Products 97

system reaches an equilibrium atmosphere containing of lower concentrations of O2 and

Product Temperature Atmosphere range (0C) %O2 %CO2 Apples 0-5 1-2 0-3 Banana 12-16 2-5 2-5 Blackberry 0-5 5-10 15-20 Blueberry 0-5 2-5 12-20 Cherry, sweet 0-5 3-10 10-15 Cranberry 2-5 1-2 0-5 Grape 0-5 2-5 1-3 Kiwifruit 0-5 1-2 3-5 Lemon 10-15 5-10 0-10 Lychee (Lichti) 5-12 3-5 3-5 Mango 10-15 3-7 5-8 Nuts and dried fruits 0-10 0-1 0-100 Orange 5-10 5-10 0-5 Papaya 10-15 2-5 5-8 Persimmon 0-15 3-5 5-8 Pineapple 8-13 2-5 5-10 Plum 0-5 1-2 0-5 Raspberry 0-5 5-10 15-20 Strawberry 0-5 5-10 15-20 Artichoke 0-5 2-3 2-3 Asparagus 1-5 Air 10-14 Beans 5-10 2-3 4-7 Broccoli 0-5 1-2 5-10 Brussels sprouts 0-5 1-2 5-7 Cabbage 0-5 2-3 3-6 Cantaloupes 2-7 3-5 10-20 Cauliflower 0-5 2-3 3-4 Celery 0-5 1-4 3-5 Cucumbers 8-12 1-4 0 Herbs\* 0-5 5-10 4-6 Lettuce 0-5 1-3 0 Onions 0-5 1-2 0-10 Parsley 0-5 8-10 8-10 Pepper 5-12 2-5 2-5 Radish 0-5 1-2 2-3 Spinach 0-5 7-10 5-10 Tomatoes 12-20 3-5 2-3

\*Herbs: chervil, chives, coriander, dill, sorrel and watercress, Adapted from Kader (2002)

transport and / or storage of fruits and vegetables

Table 1. Summary of optimal conditions for modified atmosphere and temperature during

higher concentrations of CO2 than in atmospheric air.

particularly on aspects of the respiration process, usual methods of measuring respiration rates and factors can be affect the respiration rate.

## **2. Modified atmosphere packaging**

Modified atmosphere packaging (MAP) of fresh fruits and vegetables is based on modifying the levels of O2 and CO2 in the atmosphere produced inside a package sealed with some type of polymer film. It is desirable that the natural interaction that occurs between the respiration of the product and the packaging generates an atmosphere with low levels of O2 and / or a high concentration of CO2. The growth of organisms that cause decay is thereby reduced and the life of the product is thus extended. Additionally, the desired atmosphere can reduce the respiration rate, and ethylene production, physiological changes. For example, it can inhibit chemical, enzymatic and microbiological mechanisms associated with the decay of fresh products, thus avoiding the use of other chemical or thermal process such as freezing, dehydration, and sterilization (Kader et al. 1989; Gorris & Tauscher, 1999; Saltveit, 1997; Fonseca et al., 2002).

The use of modified and controlled atmospheres has grown over the past 50 years, contributing significantly to extend the postharvest life and maintain the quality of various fruits and vegetables. So that changing the atmosphere occurs must have a combination of factors that influence the permeability of the product packaging and respiration in order to achieve an atmosphere of great balance for the conservation of the product. This balance is achieved when the respiration of the product consumes the same amount of O2 entering the packaging and the production of CO2 by respiration is equal to the amount that leaves the packaging (Day, 1993).

The first studies on modified atmospheres used reduced levels of O2 in apple packaging in order to slow the ripening of fruits. The first challenge was to control the levels of O2 in the package. Since then, an enormous variety of polymers with different properties have been developed to offer a wide range of options in features such as gas permeability, tensile strength and flexibility, among others. Presently, diverse systems of modified atmosphere packaging have been developed and used with a wide range of fruits and vegetables in order to provide optimal storage conditions and product longevity. Table 1 summarizes the optimal conditions of temperature and gas composition of O2 and CO2 for the transport and / or storage of some fruits and vegetables.

#### **2.1 Passive**

Modified atmospheres can be obtained passively between plant material and sealed package or intentionally using determined concentrations of gases. Modified atmosphere is formed as a result of vegetable respiration, which consumes CO2 and releases O2 in sealed package. In passive modification, the respiring product is placed in a polymeric package and sealed hermetically. Only the respiration of the product and the gas permeability of the film influence the change in gaseous composition of the environment surrounding the product. If the product's respiration characteristics are properly matched to the film permeability values, then a beneficial modified atmosphere can be passively created within a package. The polymer itself variably restricts gas exchange between the internal and external environments due to its selective permeability to O2 and CO2. After a period of time, the

particularly on aspects of the respiration process, usual methods of measuring respiration rates

Modified atmosphere packaging (MAP) of fresh fruits and vegetables is based on modifying the levels of O2 and CO2 in the atmosphere produced inside a package sealed with some type of polymer film. It is desirable that the natural interaction that occurs between the respiration of the product and the packaging generates an atmosphere with low levels of O2 and / or a high concentration of CO2. The growth of organisms that cause decay is thereby reduced and the life of the product is thus extended. Additionally, the desired atmosphere can reduce the respiration rate, and ethylene production, physiological changes. For example, it can inhibit chemical, enzymatic and microbiological mechanisms associated with the decay of fresh products, thus avoiding the use of other chemical or thermal process such as freezing, dehydration, and sterilization (Kader et al. 1989; Gorris & Tauscher, 1999;

The use of modified and controlled atmospheres has grown over the past 50 years, contributing significantly to extend the postharvest life and maintain the quality of various fruits and vegetables. So that changing the atmosphere occurs must have a combination of factors that influence the permeability of the product packaging and respiration in order to achieve an atmosphere of great balance for the conservation of the product. This balance is achieved when the respiration of the product consumes the same amount of O2 entering the packaging and the production of CO2 by respiration is equal to the amount that leaves the

The first studies on modified atmospheres used reduced levels of O2 in apple packaging in order to slow the ripening of fruits. The first challenge was to control the levels of O2 in the package. Since then, an enormous variety of polymers with different properties have been developed to offer a wide range of options in features such as gas permeability, tensile strength and flexibility, among others. Presently, diverse systems of modified atmosphere packaging have been developed and used with a wide range of fruits and vegetables in order to provide optimal storage conditions and product longevity. Table 1 summarizes the optimal conditions of temperature and gas composition of O2 and CO2 for the transport and

Modified atmospheres can be obtained passively between plant material and sealed package or intentionally using determined concentrations of gases. Modified atmosphere is formed as a result of vegetable respiration, which consumes CO2 and releases O2 in sealed package. In passive modification, the respiring product is placed in a polymeric package and sealed hermetically. Only the respiration of the product and the gas permeability of the film influence the change in gaseous composition of the environment surrounding the product. If the product's respiration characteristics are properly matched to the film permeability values, then a beneficial modified atmosphere can be passively created within a package. The polymer itself variably restricts gas exchange between the internal and external environments due to its selective permeability to O2 and CO2. After a period of time, the

and factors can be affect the respiration rate.

**2. Modified atmosphere packaging**

Saltveit, 1997; Fonseca et al., 2002).

/ or storage of some fruits and vegetables.

packaging (Day, 1993).

**2.1 Passive**

system reaches an equilibrium atmosphere containing of lower concentrations of O2 and higher concentrations of CO2 than in atmospheric air.

\*Herbs: chervil, chives, coriander, dill, sorrel and watercress, Adapted from Kader (2002)

Table 1. Summary of optimal conditions for modified atmosphere and temperature during transport and / or storage of fruits and vegetables

Modified Atmosphere Packaging for Perishable Plant Products 99

5 Apple (most cultivars), apricot, cauliflower, cucumber, grape, nashi, olive,

10 Asparagus, brussels sprouts, cabbage, celery, lemon, mango, nectarine, peach,

orange, peach (clingstone), potato, pepper (bell)

15 Avocado, broccoli, lychee, plum, pomegranate, sweetsop 20 Cantaloupe (muskmelon), durian, mushroom, rambutan

\*Data are from Beaudry (2000), Gorny (1997), Kader (1997), Kupferman (1997), Richardson and

Table 2. O2 limits below which injury can occur for selected horticultural crops held at

< 0.5 Chopped greenleaf, Romaine and iceberg lettuce, spinach, sliced pear, broccoli 1.0 Broccoli florets, chopped butterhead lettuce, sliced apple, brussels sprouts, cantaloupe, cucumber, crisphead lettuce, onion, apricot, avocado, banana, cherimoya, sweet cherry, cranberry, grape, kiwifruit, litchi, peach, plum 2.0 Shredded and cut carrots, artichoke, cabbage, cauliflower, celery, bell and chili pepper, sweet corn, tomato, blackberry, fig, mango, olive, papaya, pineapple,

3.0 Cubed or sliced cantaloupe, low permeability apples and pears, persimmon

Table 3. CO2 partial pressures above which injury will occur for selected horticultural crops

metabolism of the product. In addition, some carbon dioxide must exit from the package to avoid build up of injurious levels of the gas. These packages are made of plastic films with

Packaging films that provide a wide range of physical properties, many of these individual films are combined through processes like lamination and co-extrusion. There are several groupings in MAP films such as in the plural, Vinyl Polymers, Styrene Polymers,

O2 (%) Commodity

8 Papaya

2 Lettuce (crisphead), pear

7 Banana, bean (green snap), kiwi fruit

persimmon, pineapple, sweet corn

25 Blackberry, blueberry, fig, raspberry, strawberry

pomegranate, raspberry, strawberry

5.0 Green snap beans, lemon, lime, orange

\* Adapted from Herner (1987), Kader (1997), and Saltveit (1997)

2.5 Shredded cabbage, blueberry

4.0 Sliced mushrooms

relatively high gas permeability.

10.0 Asparagus 14.0 Orange sections

3 Artichoke, tomato

Kupferman (1997), and Saltveit (1997)

typical storage temperatures

CO2 (kPa) Commodity

#### **2.2 Active**

The concept of active packaging has been developed to adjust the deficiencies in passive packaging such as when a film is a good barrier to moisture, but not to oxygen, the film can still be used along with an oxygen scavenger to exclude oxygen from the pack. An intentionally or actively obtained modified atmosphere occurs when the desired gas mixture is introduced into the container before sealing. In this way, atmospheric balance inside the package is reached faster or almost immediately. Sometimes, certain additives are incorporated into the polymeric packaging film or within packaging containers to modify the headspace atmosphere and to extend shelf-life. Another process is the acceleration of atmospheric balance under partial vacuum packaging is the process of removing the air before sealing, reducing the free space. Although the active modification of the atmosphere within the package incurrs additional costs, the advantage is that the desired atmosphere is securely achieved in considerably less time.

### **2.3 O2 and CO2 limits**

Safe levels of O2 and CO2 are important for package design. A lower O2 limit has been associated with onset of fermentation and accumulation of ethanol and acetaldehyde (Beaudry et al., 1993). Fermentation is linked to the development of off-flavors and/or tissue damage. Effect of temperature on lower O2 limit has been measured for a number of commodities including whole apple, apple slices, blueberry, and raspberry. In each case, lower O2 limit increased with temperature. Lower O2 limits vary from 0.15% to 5% and are influenced by temperature, commodity and cultivar (Beaudry and Gran, 1993).

It is necessary to know the main effects of gases on fresh fruits and vegetables and the interactions between gas and produce on the one hand and between gas and packaging material on the other hand to achieve the goal. It is important to recognize that while atmosphere modification can improve the storability of some fruits and vegetables, it also has the potential to induce undesirable effects. Fermentation and off-flavors may develop if decreased O2 levels cannot sustain aerobic respiration (Kays, 1997). Similarly, injury will occur if CO2 exceeds tolerable levels. Ranges of non-damaging O2 and CO2 levels have been published for a numbers of fruits and vegetables (Kader, 1997; Kupferman, 1997; Richardson and Kupferman, 1997; Saltveit, 1997; Beaudry 1999, 2000), minimally processed products (Gorny, 1997), and flowers and ornamentals (Reid, 1997). Horticultural crops differ in their tolerance for O2 (Table 2) and CO2 (Table 3).

### **3. Types of plastic films used in MAP**

In a modified atmosphere packaging, changes start to take place immediately after packing the fresh produce as a result of the respiration of the packaged produce. The gases of the contained atmosphere and the external ambient atmosphere try to equilibrate by permeation through the package walls at a rate dependant upon the differential pressures between the gases of the headspace and those of the ambient atmosphere. It is in this context that the barrier to gases and water vapor provided by the packaging material must be considered. Thus, the success of the modified atmosphere packaging depends upon the barrier material used. MAP for fresh produce must also allow entry of oxygen to maintain the aerobic

The concept of active packaging has been developed to adjust the deficiencies in passive packaging such as when a film is a good barrier to moisture, but not to oxygen, the film can still be used along with an oxygen scavenger to exclude oxygen from the pack. An intentionally or actively obtained modified atmosphere occurs when the desired gas mixture is introduced into the container before sealing. In this way, atmospheric balance inside the package is reached faster or almost immediately. Sometimes, certain additives are incorporated into the polymeric packaging film or within packaging containers to modify the headspace atmosphere and to extend shelf-life. Another process is the acceleration of atmospheric balance under partial vacuum packaging is the process of removing the air before sealing, reducing the free space. Although the active modification of the atmosphere within the package incurrs additional costs, the advantage is that the desired atmosphere is

Safe levels of O2 and CO2 are important for package design. A lower O2 limit has been associated with onset of fermentation and accumulation of ethanol and acetaldehyde (Beaudry et al., 1993). Fermentation is linked to the development of off-flavors and/or tissue damage. Effect of temperature on lower O2 limit has been measured for a number of commodities including whole apple, apple slices, blueberry, and raspberry. In each case, lower O2 limit increased with temperature. Lower O2 limits vary from 0.15% to 5% and are

It is necessary to know the main effects of gases on fresh fruits and vegetables and the interactions between gas and produce on the one hand and between gas and packaging material on the other hand to achieve the goal. It is important to recognize that while atmosphere modification can improve the storability of some fruits and vegetables, it also has the potential to induce undesirable effects. Fermentation and off-flavors may develop if decreased O2 levels cannot sustain aerobic respiration (Kays, 1997). Similarly, injury will occur if CO2 exceeds tolerable levels. Ranges of non-damaging O2 and CO2 levels have been published for a numbers of fruits and vegetables (Kader, 1997; Kupferman, 1997; Richardson and Kupferman, 1997; Saltveit, 1997; Beaudry 1999, 2000), minimally processed products (Gorny, 1997), and flowers and ornamentals (Reid, 1997). Horticultural crops differ in their

In a modified atmosphere packaging, changes start to take place immediately after packing the fresh produce as a result of the respiration of the packaged produce. The gases of the contained atmosphere and the external ambient atmosphere try to equilibrate by permeation through the package walls at a rate dependant upon the differential pressures between the gases of the headspace and those of the ambient atmosphere. It is in this context that the barrier to gases and water vapor provided by the packaging material must be considered. Thus, the success of the modified atmosphere packaging depends upon the barrier material used. MAP for fresh produce must also allow entry of oxygen to maintain the aerobic

influenced by temperature, commodity and cultivar (Beaudry and Gran, 1993).

**2.2 Active**

securely achieved in considerably less time.

tolerance for O2 (Table 2) and CO2 (Table 3).

**3. Types of plastic films used in MAP**

**2.3 O2 and CO2 limits**

\*Data are from Beaudry (2000), Gorny (1997), Kader (1997), Kupferman (1997), Richardson and Kupferman (1997), and Saltveit (1997)

Table 2. O2 limits below which injury can occur for selected horticultural crops held at typical storage temperatures

\* Adapted from Herner (1987), Kader (1997), and Saltveit (1997)

Table 3. CO2 partial pressures above which injury will occur for selected horticultural crops

metabolism of the product. In addition, some carbon dioxide must exit from the package to avoid build up of injurious levels of the gas. These packages are made of plastic films with relatively high gas permeability.

Packaging films that provide a wide range of physical properties, many of these individual films are combined through processes like lamination and co-extrusion. There are several groupings in MAP films such as in the plural, Vinyl Polymers, Styrene Polymers,

Modified Atmosphere Packaging for Perishable Plant Products 101

Mathematical models can integrate the film permeability to O2, CO2 and H2O, and the respiratory response of the commodity to O2, in some cases, CO2, along with its lower O2 limit and upper CO2 limit (Beaudry et al., 1992; Cameron et al., 1994; Lakakul et al., 1999; Fishman et al., 1996; Hertog et al., 1998). These models permit the identification of limiting

The major factors to be taken into account while selecting the packaging materials are the type of package, the barrier properties needed (permeabilities of individual gases and gas ratios when more than one gas is used), physical properties of machinability and strength, integrity of closure (heat sealing), fogging of the film as a result of product respiration,

Respiration is a process in which chemical reactions oxidize lipids and carbohydrates to carbon dioxide and water to produce energy, while the organelle responsible for aerobic respiration known as mitochondria. Part of the released energy is stored as chemical energy adenosine triphosphate (ATP) and part is lost as heat. This complex process can be influenced by several intrinsic factors such as product size, variety, maturity, type of tissue and extrinsic factors such as temperature, concentration of O2 and CO2 and mechanical

Knowledge of the minimum required for O2 aerobic respiration is very important to avoid that the anaerobic pathway is the predominant route of respiration, which causes the accelerated loss of product quality. In order to maintain food safety, it is important to know the potential hazards of each product, the permeability of the films and the rate of

Since both the rate of respiration and the permeability of the film are sensitive to temperature variations, and respond to these changes differently, it is expected that the package under modified atmosphere remains determined only within an atmosphere given

The maximal rate of respiration for most fruit and vegetable products undergoes a 4- to 6 fold increase from 0 to 15 °C (Beaudry et al., 1992; Cameron et al., 1994, 1995; Lakakul et al., 1999). This means that product respiration increases at two or three times the rate of LDPE permeability, and thirty times the rate of perforation permeability with increasing temperature. When respiratory demand for O2 increases faster than O2 permeation as temperature increases, O2 levels decline and may pose a risk to product quality. This limits

Variation in the respiration rate of the product and the variation in film or permeability can influence package design. Variation in product respiration and package permeability has been measured for broccoli and the effect on package O2 modeled (Cameron et al., 1993). Cameron et al. (1993) concluded that there is an estimable risk of the package O2 falling sufficiently low to promote fermentation in any product. Packages should be designed to generate O2 levels well above the lower limit to ensure aerobic conditions. Products such as broccoli, mushrooms, leeks and others have very high rates of respiration, and most continuous films do not have the capacity to provide enough O2 to avoid fermentation.

respiration of fruits and vegetables (Watada et al., 1996).

features of the film, package design, and product and environment conditions.

printability and others.

**4.1 Respiration rate**

damage (Day, 1993).

temperature range (Zagory, 2000).

the usefulness of MAP in some situations.

Polyamides, Polyesters and other polymers. Polypropylene is part of the Polyolefin group and used largely in MAP, in both forms: continuous and perforated. Sanz et al. (1999) studied the quality of strawberries packaged with polypropylene film, with proper perforations, during commercial postharvest practices. They concluded that perforatedmediated MA packaging helped to preserve fruit ripeness degree better, maintaining its nutritional value, measured as ascorbic acid content.

Many type of plastic films for packaging are available, but relatively few have been used to pack fresh fruits and vegetables, and even fewer have a gas permeability that makes them suitable for modified atmosphere packaging. The permeability of CO2 should be 3 to 5 times the permeability of O2. Many polymers used to formulate packaging films are within this criterion (Table 4).

\*Adapted from Kader (2002)

Table 4. Permeability for packaging fresh fruits and vegetables

## **4. Package parameters**

Modified atmosphere (MA) packaging systems designed to produce optimum O2 and CO2 concentrations at suitable temperatures have been mathematically modeled (Chinnan, 1989; Lee et al., 1991; Exama et al., 1993; Talasila et al., 1995; Cameron et al., 1995).

The composition of the atmosphere inside the packaging results from the interaction of several factors including the permeability characteristics of the packaging material, the respiratory behavior of the plant material and the environment. Packaging films are selected so that the package has specific permeability characteristics and so that changes to these characteristics (temperature and humidity) over time, following the laws of physics. The concentration of gases within the packaging can be controlled to provide specific conditions. In contrast to these known and controllable factors are the often unknown and uncontrollable responses of the plant material. The plant species, the cultivar, cultural practices, the development stage, harvest management, the tissue type and post harvest handling all contribute and influence the response of the material to the atmosphere generated.

The scope of plant responses can be modified by the initial flow of gas before sealing the packaging as well as by the inclusion of chemical treatments to slow undesirable processes or decrease contamination. Each component of the packaging process needs to be examined separately to improve the understanding of what it contributes to potential packaging strategies.

Mathematical models can integrate the film permeability to O2, CO2 and H2O, and the respiratory response of the commodity to O2, in some cases, CO2, along with its lower O2 limit and upper CO2 limit (Beaudry et al., 1992; Cameron et al., 1994; Lakakul et al., 1999; Fishman et al., 1996; Hertog et al., 1998). These models permit the identification of limiting features of the film, package design, and product and environment conditions.

The major factors to be taken into account while selecting the packaging materials are the type of package, the barrier properties needed (permeabilities of individual gases and gas ratios when more than one gas is used), physical properties of machinability and strength, integrity of closure (heat sealing), fogging of the film as a result of product respiration, printability and others.

## **4.1 Respiration rate**

100 Polypropylene

Polyamides, Polyesters and other polymers. Polypropylene is part of the Polyolefin group and used largely in MAP, in both forms: continuous and perforated. Sanz et al. (1999) studied the quality of strawberries packaged with polypropylene film, with proper perforations, during commercial postharvest practices. They concluded that perforatedmediated MA packaging helped to preserve fruit ripeness degree better, maintaining its

Many type of plastic films for packaging are available, but relatively few have been used to pack fresh fruits and vegetables, and even fewer have a gas permeability that makes them suitable for modified atmosphere packaging. The permeability of CO2 should be 3 to 5 times the permeability of O2. Many polymers used to formulate packaging films are within this

 CO2 O2 CO2:O2 ratio Polyester 180-390 52-130 3.0-3.5 Polyethylene, low density 7,700-77,000 3,900-13,000 2.0-5.9 Polypropylene 7,700-21,000 1,300-6,400 3.3-5.9 Polystrene 10,000-26,000 2,600-7,700 3.4-3.8 Polyvinyl chloride 4,263-8,138 620-2,248 3.6-6.9

Modified atmosphere (MA) packaging systems designed to produce optimum O2 and CO2 concentrations at suitable temperatures have been mathematically modeled (Chinnan, 1989;

The composition of the atmosphere inside the packaging results from the interaction of several factors including the permeability characteristics of the packaging material, the respiratory behavior of the plant material and the environment. Packaging films are selected so that the package has specific permeability characteristics and so that changes to these characteristics (temperature and humidity) over time, following the laws of physics. The concentration of gases within the packaging can be controlled to provide specific conditions. In contrast to these known and controllable factors are the often unknown and uncontrollable responses of the plant material. The plant species, the cultivar, cultural practices, the development stage, harvest management, the tissue type and post harvest handling all contribute and influence

The scope of plant responses can be modified by the initial flow of gas before sealing the packaging as well as by the inclusion of chemical treatments to slow undesirable processes or decrease contamination. Each component of the packaging process needs to be examined separately to improve the understanding of what it contributes to potential packaging

Lee et al., 1991; Exama et al., 1993; Talasila et al., 1995; Cameron et al., 1995).

(cc/m2/mil/dia a 1 atm)

nutritional value, measured as ascorbic acid content.

Film type Permeabilities

Table 4. Permeability for packaging fresh fruits and vegetables

the response of the material to the atmosphere generated.

criterion (Table 4).

\*Adapted from Kader (2002)

**4. Package parameters**

strategies.

Respiration is a process in which chemical reactions oxidize lipids and carbohydrates to carbon dioxide and water to produce energy, while the organelle responsible for aerobic respiration known as mitochondria. Part of the released energy is stored as chemical energy adenosine triphosphate (ATP) and part is lost as heat. This complex process can be influenced by several intrinsic factors such as product size, variety, maturity, type of tissue and extrinsic factors such as temperature, concentration of O2 and CO2 and mechanical damage (Day, 1993).

Knowledge of the minimum required for O2 aerobic respiration is very important to avoid that the anaerobic pathway is the predominant route of respiration, which causes the accelerated loss of product quality. In order to maintain food safety, it is important to know the potential hazards of each product, the permeability of the films and the rate of respiration of fruits and vegetables (Watada et al., 1996).

Since both the rate of respiration and the permeability of the film are sensitive to temperature variations, and respond to these changes differently, it is expected that the package under modified atmosphere remains determined only within an atmosphere given temperature range (Zagory, 2000).

The maximal rate of respiration for most fruit and vegetable products undergoes a 4- to 6 fold increase from 0 to 15 °C (Beaudry et al., 1992; Cameron et al., 1994, 1995; Lakakul et al., 1999). This means that product respiration increases at two or three times the rate of LDPE permeability, and thirty times the rate of perforation permeability with increasing temperature. When respiratory demand for O2 increases faster than O2 permeation as temperature increases, O2 levels decline and may pose a risk to product quality. This limits the usefulness of MAP in some situations.

Variation in the respiration rate of the product and the variation in film or permeability can influence package design. Variation in product respiration and package permeability has been measured for broccoli and the effect on package O2 modeled (Cameron et al., 1993). Cameron et al. (1993) concluded that there is an estimable risk of the package O2 falling sufficiently low to promote fermentation in any product. Packages should be designed to generate O2 levels well above the lower limit to ensure aerobic conditions. Products such as broccoli, mushrooms, leeks and others have very high rates of respiration, and most continuous films do not have the capacity to provide enough O2 to avoid fermentation.

Modified Atmosphere Packaging for Perishable Plant Products 103

dioxide and / or lower in oxygen is required, the material should be impermeable to the gases. Vegetables and fruits require a certain amount of oxygen in the headspace for maintenance of quality, therefore, packaging material for these products should be quite permeable to the oxygen, to allow atmospheric oxygen to replenish the gas in the package.

The choice of packaging material is an extremely important part of the MAP operation. The materials must be cost effective, have low water vapor transmission rate, high gas barrier, mechanical strength to withstand machine handling and subsequent storage and distribution of the finished pack as well as have the capability of giving high integrity seals to ensure retention of gas within the pack until opened by consumer. Also, once a gas atmosphere is applied, the level and proportion of headspace gas/gases is controlled only by judicious selection of packaging material with specified permeability characteristics. .

There are two ways to create barriers using film. The first strategy employs continuous films that control the movement of gases in and out of the box. The second strategy uses film with

With continuous films, the movement of O2 and CO2 is directly proportional to the differences in gas concentration across the film. Constant levels of gases in the package are achieved when the product's consumption of O2 and production of CO2 are equal. This

In perforated films, the rate of movement of gas through the perforated film is the sum of gas diffusion and atmospheric air infiltration through the polymer film. Generally, total gas flow through the perforations is much greater than gas movement through the film. The rate of gas exchange through microperforations is much greater than through continuous films. Perforated packaging is more suitable for vegetables that have a high demand for O2

The respiration rate of fresh fruits and vegetables can be expressed as the rate of O2 consumption and CO2 production rate. The usual methods for determining the concentration of respiration are static or closed system, continuous flow system, and permeable system. The respiration rate is measured in permeable system, in other words, the product is within the dimensions and permeability of packaging film known (Beaudry, 1993; Joles et al., 1994; Lakakul, Beaudry, & Hernandez, 1999; Lee, Song, & Yam, 1996; Piergiovanni, Fava, & Ceriani, 1999; Smyth et al., 1998). The concentrations of O2 and CO2 are determined and stable mass balance is done on the system in order to estimate

The concentrations of gases in the system depend on the permeability characteristics of permeability, package size and weight of the product that were discussed previously. The time to reach equilibrium can be seen as a limitation of this method to measure the respiration rate. Definition of the steady-state concentration values is another difficulty of

situation exists only when the respiration rate is constant (Fishman et al., 1996).

Transparency of packaging material to light is also important.

Thickness is also a factor controlling permeability.

small openings or microperforations.

**5. Respiration rate measurement**

(Gonzalez et al., 2008).

respiration rates.

the permeable method.

Accordingly, there is commercial interest to develop films with high gas transmission rates. Films that have improved rates of gas transmission by virtue of their polymeric nature are often blends of two or three different polymers, where each polymer performs a specific function such as strength, transparency and improved gas transmission. Similarly, films can be laminated to achieve needed properties.

## **4.2 Temperature**

Temperature is one of the most important factors in extending the shelf-life of perishable products. Optimum storage temperature must be established for every product. Permeability of polymeric packaging films is also a function of temperature and it generally increases with the increase in temperature.

The effects of temperature on chemical reactions, including respiratory rate, traditionally quantified by Q10, which is a coefficient by which it is possible to calculate how many times increases the rate of a reaction for each increase in temperature of 10 °C. The effect of temperature can also be quantified by the Arrhenius model, where the effect of temperature increase is given by the activation energy (Ea) (Cameron et al., 1995). The temperature quotient is useful because it allows us to calculate the respiration rates at one temperature from a known rate at another temperature. However, the respiration rate does not follow ideal behavior, and the Q10 can vary considerably with temperature. At higher temperatures, the Q10 is usually smaller than at lower temperatures.

The storage temperature is very important for the evolution of microbial and visual quality of fresh fruits and vegetables. Knowledge of weather conditions and temperature in the cold chain for fresh produce is needed to determine the influence of the cold chain in real loss of quality and shelf life of these products (Cortez et al., 2002).

The temperature of the produce in the package is managed by circulating cool air around the outside of the package. The film and the headspace atmosphere are barriers to heat movement, prevent rapid cooling, and reduce the effectiveness of refrigeration. A 'safe radius' for the distance from the center of the package to the circulated air can be calculated based on the heat of respiration and the rate at which heat can be removed by the cooler air (Sharp et al., 1993). For instance, the center of a package of broccoli must have a radius of less than 14 cm to keep it within 1 °C of the refrigerated air.

Temperature control, when combined with correct use of packaging and modified atmosphere technology, is effective in controlling metabolic processes described above. However, the ideal temperature handling, storage and marketing of fresh fruits and vegetable is generally not respected. Some examples of the ranges of temperature and relative humidity are to be respected in Table 1.

If it is necessary to choose between mild temperatures that cause symptoms of chilling injury and temperatures accelerate senescence and microbial growth, the first must be chosen (Watada and Qi, 1999).

#### **4.3 Permeability**

The permeability of the packaging material determines the atmospheric conditions in the headspace and ultimately the shelf-life of the product. If an atmosphere higher in carbon

Accordingly, there is commercial interest to develop films with high gas transmission rates. Films that have improved rates of gas transmission by virtue of their polymeric nature are often blends of two or three different polymers, where each polymer performs a specific function such as strength, transparency and improved gas transmission. Similarly, films can

Temperature is one of the most important factors in extending the shelf-life of perishable products. Optimum storage temperature must be established for every product. Permeability of polymeric packaging films is also a function of temperature and it generally

The effects of temperature on chemical reactions, including respiratory rate, traditionally quantified by Q10, which is a coefficient by which it is possible to calculate how many times increases the rate of a reaction for each increase in temperature of 10 °C. The effect of temperature can also be quantified by the Arrhenius model, where the effect of temperature increase is given by the activation energy (Ea) (Cameron et al., 1995). The temperature quotient is useful because it allows us to calculate the respiration rates at one temperature from a known rate at another temperature. However, the respiration rate does not follow ideal behavior, and the Q10 can vary considerably with temperature. At higher temperatures,

The storage temperature is very important for the evolution of microbial and visual quality of fresh fruits and vegetables. Knowledge of weather conditions and temperature in the cold chain for fresh produce is needed to determine the influence of the cold chain in real loss of

The temperature of the produce in the package is managed by circulating cool air around the outside of the package. The film and the headspace atmosphere are barriers to heat movement, prevent rapid cooling, and reduce the effectiveness of refrigeration. A 'safe radius' for the distance from the center of the package to the circulated air can be calculated based on the heat of respiration and the rate at which heat can be removed by the cooler air (Sharp et al., 1993). For instance, the center of a package of broccoli must have a radius of

Temperature control, when combined with correct use of packaging and modified atmosphere technology, is effective in controlling metabolic processes described above. However, the ideal temperature handling, storage and marketing of fresh fruits and vegetable is generally not respected. Some examples of the ranges of temperature and

If it is necessary to choose between mild temperatures that cause symptoms of chilling injury and temperatures accelerate senescence and microbial growth, the first must be

The permeability of the packaging material determines the atmospheric conditions in the headspace and ultimately the shelf-life of the product. If an atmosphere higher in carbon

be laminated to achieve needed properties.

increases with the increase in temperature.

the Q10 is usually smaller than at lower temperatures.

quality and shelf life of these products (Cortez et al., 2002).

less than 14 cm to keep it within 1 °C of the refrigerated air.

relative humidity are to be respected in Table 1.

chosen (Watada and Qi, 1999).

**4.3 Permeability**

**4.2 Temperature**

dioxide and / or lower in oxygen is required, the material should be impermeable to the gases. Vegetables and fruits require a certain amount of oxygen in the headspace for maintenance of quality, therefore, packaging material for these products should be quite permeable to the oxygen, to allow atmospheric oxygen to replenish the gas in the package.

Transparency of packaging material to light is also important.

The choice of packaging material is an extremely important part of the MAP operation. The materials must be cost effective, have low water vapor transmission rate, high gas barrier, mechanical strength to withstand machine handling and subsequent storage and distribution of the finished pack as well as have the capability of giving high integrity seals to ensure retention of gas within the pack until opened by consumer. Also, once a gas atmosphere is applied, the level and proportion of headspace gas/gases is controlled only by judicious selection of packaging material with specified permeability characteristics. . Thickness is also a factor controlling permeability.

There are two ways to create barriers using film. The first strategy employs continuous films that control the movement of gases in and out of the box. The second strategy uses film with small openings or microperforations.

With continuous films, the movement of O2 and CO2 is directly proportional to the differences in gas concentration across the film. Constant levels of gases in the package are achieved when the product's consumption of O2 and production of CO2 are equal. This situation exists only when the respiration rate is constant (Fishman et al., 1996).

In perforated films, the rate of movement of gas through the perforated film is the sum of gas diffusion and atmospheric air infiltration through the polymer film. Generally, total gas flow through the perforations is much greater than gas movement through the film. The rate of gas exchange through microperforations is much greater than through continuous films. Perforated packaging is more suitable for vegetables that have a high demand for O2 (Gonzalez et al., 2008).

## **5. Respiration rate measurement**

The respiration rate of fresh fruits and vegetables can be expressed as the rate of O2 consumption and CO2 production rate. The usual methods for determining the concentration of respiration are static or closed system, continuous flow system, and permeable system. The respiration rate is measured in permeable system, in other words, the product is within the dimensions and permeability of packaging film known (Beaudry, 1993; Joles et al., 1994; Lakakul, Beaudry, & Hernandez, 1999; Lee, Song, & Yam, 1996; Piergiovanni, Fava, & Ceriani, 1999; Smyth et al., 1998). The concentrations of O2 and CO2 are determined and stable mass balance is done on the system in order to estimate respiration rates.

The concentrations of gases in the system depend on the permeability characteristics of permeability, package size and weight of the product that were discussed previously. The time to reach equilibrium can be seen as a limitation of this method to measure the respiration rate. Definition of the steady-state concentration values is another difficulty of the permeable method.

Modified Atmosphere Packaging for Perishable Plant Products 105

Indeed the most important factor affecting postharvest life is temperature. This is because temperature has a profound effect on the rates of biological reactions, specifically metabolism and respiration. Over the physiological range of most crops, 0 to 30 °C increased

Temperature of the product affects storability more than any other factor. Pre-cooling and temperature maintenance during handling and shipping are critical in preserving quality. Temperature also significantly affects film permeability and thereby the O2 and CO2 content

The elevated rate of respiration at high temperature could be used to rapidly establish the desired package atmosphere, but this would only be useful in the few situations in which it would be more important to rapidly establish the atmosphere than to slow physiological

Another solution to the MAP temperature problem is to develop a package system that senses either the environment or the physiological status of the enclosed product and responds by increasing the permeability to O2 (Cameron et al., 1993). Such 'sense-andrespond' packaging is technically difficult to develop, and progress has only been conceptual at this time (Smyth et al., 1999). A third approach is to design packages to function at the highest temperatures typically encountered in the distribution and retail cool chain and, as far as possible, maintain control over the temperature of the packaged product, thereby adapting to the limitations imposed by the film. Most companies using MAP have adopted this simple solution. Generally, the lowest temperature feasible is maintained, since temperature has a much more significant influence on preserving quality

Reações metabólicas, entre elas a respiração, são reduzidas em 2 a 3 vezes para cada decréscimo de 10 °C na temperatura, o que permite retardar a maturação e a senescência do

In MAP, the pack is flushed with a gas or a combination of gases. The common gases used are oxygen, nitrogen and carbon dioxide. Traces of carbon monoxide, nitrous oxide, ozone, argon, ethanol vapour and sulphur dioxide are also used. Minimum oxygen levels are used to pack plant under MA because oxygen can react with the fruits and vegetables resulting in the oxidative breakdown of them into their constitutive parts. Nitrogen is an inert gas. Carbon dioxide is responsible for the bacteriostatic and fungistatic effect in MA packaged fruits and vegetables. It retards the growth of moulds and aerobic bacteria. The inhibitory effect of carbon dioxide to micro-organisms is increased as the temperature is lowered.

The tolerance of any plant tissue at low O2 tension is smaller as the storage temperature increases, since the requirements for aerobic respiration of the tissue increases with increasing temperature. Depending on the product damage associated with CO2 can both increase and decrease with rise in temperature. CO2 production increases with temperature, but its solubility decreases. Thus, the CO2 concentration in the tissue may decrease or increase with increasing temperature. In addition, the physiological effect of CO2 could be

**5.2 Inuence of temperature**

of the package.

temperatures cause an exponential rise in respiration.

processes, eg., to reduce cut-surface browning.

than the application of low O2 (Kays, 1997).

**5.3 Inuence of gas composition**

produto (Brecht, 1995).

temperature dependent.

For all methods have limitations, but this involves a greater number of variables, since the size of the packet are involved other parameters such as free volume, surface area and thickness of the gas exchange and the permeability characteristics. None of methods is clearly preferable over the others. When choosing the respiration rate determination method for a specific study, the benefits and limitations of each method should be taken into consideration. Fonseca et al. (1992) studied three different methods (closed, flow through and permeable systems) to measure respiration rate and observed their advantages and limitations. The main characteristics of these methods are summarized in Table 5.

\*Adapted from Fonseca et al. (1992)

Table 5. Main characteristics of the three methods of respiration rate measurement

#### **5.1 Factors affecting respiration rate**

The factors affecting respiration are type and maturity stage of the commodity. Vegetables include a great diversity of plant organs such as roots, tubers, seeds, bulbs, fruits, sprouts, stems and leaves that have different metabolic activities and consequently different respiration rates. Even different varieties of the same product can exhibit different respiration rates (Fidler & North, 1967; Gran & Beaudry, 1992; Song et al., 1992). In general, non-climacteric commodities have higher respiration rates in the early stages of development that steadily decline during maturation (Lopez-Galvez, El-Bassuoni, Nie, & Cantwell, 2004). Respiration can also be affected by a wide range of environmental factors that include light, chemical stress, radiation stress, water stress, growth regulators, and pathogen attack. The most important postharvest factors are temperature, atmospheric composition, and physical stress.

One method to improve these problems would be to choose a film with permeability changes for O2 similar to that of the respiration of the product, so if temperature increases, respiration and permeability of the film increase an equivalent amount.

## **5.2 Inuence of temperature**

104 Polypropylene

For all methods have limitations, but this involves a greater number of variables, since the size of the packet are involved other parameters such as free volume, surface area and thickness of the gas exchange and the permeability characteristics. None of methods is clearly preferable over the others. When choosing the respiration rate determination method for a specific study, the benefits and limitations of each method should be taken into consideration. Fonseca et al. (1992) studied three different methods (closed, flow through and permeable systems) to measure respiration rate and observed their advantages and

Closed Flow through Permeable

Simple Complex Complex

x

x

Free volume Flow-rate Permeability package

dimensions, steadystate concentrations

x

limitations. The main characteristics of these methods are summarized in Table 5.

Non-destructive Complexity of experimental set-up

Table 5. Main characteristics of the three methods of respiration rate measurement

The factors affecting respiration are type and maturity stage of the commodity. Vegetables include a great diversity of plant organs such as roots, tubers, seeds, bulbs, fruits, sprouts, stems and leaves that have different metabolic activities and consequently different respiration rates. Even different varieties of the same product can exhibit different respiration rates (Fidler & North, 1967; Gran & Beaudry, 1992; Song et al., 1992). In general, non-climacteric commodities have higher respiration rates in the early stages of development that steadily decline during maturation (Lopez-Galvez, El-Bassuoni, Nie, & Cantwell, 2004). Respiration can also be affected by a wide range of environmental factors that include light, chemical stress, radiation stress, water stress, growth regulators, and pathogen attack. The most important postharvest factors are temperature, atmospheric

One method to improve these problems would be to choose a film with permeability changes for O2 similar to that of the respiration of the product, so if temperature increases,

respiration and permeability of the film increase an equivalent amount.

Characteristics System

Ability to test different combinations of gases

during the experiment

products

products

determination of

Suitable for low respiring

Suitable for high respiring

Accuracy is very sensitive to

\*Adapted from Fonseca et al. (1992)

composition, and physical stress.

**5.1 Factors affecting respiration rate**

Concentration is kept constant

Indeed the most important factor affecting postharvest life is temperature. This is because temperature has a profound effect on the rates of biological reactions, specifically metabolism and respiration. Over the physiological range of most crops, 0 to 30 °C increased temperatures cause an exponential rise in respiration.

Temperature of the product affects storability more than any other factor. Pre-cooling and temperature maintenance during handling and shipping are critical in preserving quality. Temperature also significantly affects film permeability and thereby the O2 and CO2 content of the package.

The elevated rate of respiration at high temperature could be used to rapidly establish the desired package atmosphere, but this would only be useful in the few situations in which it would be more important to rapidly establish the atmosphere than to slow physiological processes, eg., to reduce cut-surface browning.

Another solution to the MAP temperature problem is to develop a package system that senses either the environment or the physiological status of the enclosed product and responds by increasing the permeability to O2 (Cameron et al., 1993). Such 'sense-andrespond' packaging is technically difficult to develop, and progress has only been conceptual at this time (Smyth et al., 1999). A third approach is to design packages to function at the highest temperatures typically encountered in the distribution and retail cool chain and, as far as possible, maintain control over the temperature of the packaged product, thereby adapting to the limitations imposed by the film. Most companies using MAP have adopted this simple solution. Generally, the lowest temperature feasible is maintained, since temperature has a much more significant influence on preserving quality than the application of low O2 (Kays, 1997).

Reações metabólicas, entre elas a respiração, são reduzidas em 2 a 3 vezes para cada decréscimo de 10 °C na temperatura, o que permite retardar a maturação e a senescência do produto (Brecht, 1995).

### **5.3 Inuence of gas composition**

In MAP, the pack is flushed with a gas or a combination of gases. The common gases used are oxygen, nitrogen and carbon dioxide. Traces of carbon monoxide, nitrous oxide, ozone, argon, ethanol vapour and sulphur dioxide are also used. Minimum oxygen levels are used to pack plant under MA because oxygen can react with the fruits and vegetables resulting in the oxidative breakdown of them into their constitutive parts. Nitrogen is an inert gas. Carbon dioxide is responsible for the bacteriostatic and fungistatic effect in MA packaged fruits and vegetables. It retards the growth of moulds and aerobic bacteria. The inhibitory effect of carbon dioxide to micro-organisms is increased as the temperature is lowered.

The tolerance of any plant tissue at low O2 tension is smaller as the storage temperature increases, since the requirements for aerobic respiration of the tissue increases with increasing temperature. Depending on the product damage associated with CO2 can both increase and decrease with rise in temperature. CO2 production increases with temperature, but its solubility decreases. Thus, the CO2 concentration in the tissue may decrease or increase with increasing temperature. In addition, the physiological effect of CO2 could be temperature dependent.

Modified Atmosphere Packaging for Perishable Plant Products 107

The benefits of MAP technology to the manufacturer, retailer as well as consumer far outweigh the drawbacks. Nevertheless some critical points should be considered in this

Increased shelf-life allowing lesser frequency of loading of retail display shelves.

Reduction in production and storage costs due to better utilization of space and

Temperature control is of critical importance and, by itself, has a greater impact

Potential growth of food borne pathogens due to non-maintenance of required

Abeles, F. B., Morgan, P. W., & Saltveit, M. E. *Ethylene in plant biology*. 2nd ed. San Diego:

Beaudry, R.M., & Gran, C. D. (1993). Using a modified-atmosphere packaging approach to

Beaudry, R. M. (2000). Responses of horticultural commodities to low oxygen: limits to the

Beaudry, R. M. (1999). Effect of O2 and CO2 partial pressure on selected phenomena affecting fruit and vegetable quality. *Postharvest Biol. Technol.*, Vol 14, pp. 293-303. Beaudry, R. M., Cameron, A. C., Shirazi, A, & Dostal-Lange, D. L. (1992). Modified-

Beaudry, R. M., & Gran, C. D. (1993). Using a modified-atmosphere packaging approach to

Boyette, M.D., Sanders, D.C., & Rutledge, G.A. (1996). Package requirements for fresh fruits

Brecht, J. K. (1995). Physiology of lightly processed fruits and vegetables. *HortScience,* Vol.

answer some postharvest questions: Factors affecting the lower oxygen limit. *Acta*

expanded use of modified atmosphere packaging. *HortTechnology*, Vol. 10, pp. 491-

atmosphere packaging of blueberry fruit: Effect of temperature on package O2 and

answer some postharvest questions: Factors affecting the lower oxygen limit. *Acta*

and vegetables. The North Carolina Agricultural Extension Service. North Carolina State University, Ralley, NC. USA. Publication no 9/96-3m-TWK-260373-AG-414-8.

technology. The following list some advantages and disadvantages of MAP.

Hygienic stackable pack sealed and free from product drip and odor

Increased pack volume increases transport costs and retail display space

**7. Conclusions**

Advantages

Disadvantages

**8. References**

500.

Improved presentation of the product

equipment.

Shelf-life can be increase by 50 to 400%.

Capital cost of gas packaging machinery

Cost of gases and packaging materials

Academic Press, 1992. 414 p.

*Hort*., Vol. 362, pp. 203-212.

*Hort.* Vol. 362, pp. 203-212.

30, No. 1, pp. 18-21.

than atmosphere modification for most products

storage temperature by retailers and consumers.

CO2. *Amer. Soc. Hort.* Vol. 117, pp. 436-441.

The activation energy is a parameter that has been used to characterize plastic packaging. Knowledge of the activation energy of the breath of product and packaging serves as an important tool to predict the effects of temperature fluctuations on the concentration of gases inside the package (Cameron et al., 1995).

## **6. Plant responses of MAP**

Some of the most important factors that affect shelf life of fresh horticultural products are ripening and/or senescence, decay, and cut surface browning. The effect of modified atmosphere on these factors has been studied for different crops. The application of MA to affect these limiting factors can be restricted for some crops by adverse and/or nonbeneficial physiological responses. Additionally, the good temperature management should be associated to by atmosphere modification.

Low O2 and elevated CO2 concentrations can significantly reduce the rates of ripening and senescence primarily by reducing the synthesis and perception of ethylene (Burg and Burg, 1967; Abeles et al., 1992). Changes in respiration and starch, sugars, chlorophyll, and cell wall constituents during this period can be reduced, and in some cases nearly arrested, by eliminating ethylene action through the use of low O2/high CO2 atmospheres.

Chlorophyll loss, a desirable trait for many climacteric fruits, results in quality loss for many vegetables. Chlorophyll degradation during the senescence of green vegetables can be reduced by low O2 and elevated CO2 (Ku and Wills, 1999).

Modified atmospheres are most effective at reducing ripening prior to the onset of ripening, rather than at a later stage. At the same time, packaged fruits and vegetables are usually intended for immediate consumption by the consumer and an unripe product is not immediately edible or is of reduced quality relative to the ripe product. Thus, the advantage of extend shelf-life by retarding ripening runs counter to the needs of the consumer when retail MAP systems are used. Nevertheless, MAP can reduce the rate of ripening of some commodities such as tomato even during its later stages (Yang and Chinnan, 1988).

Decay control is a particularly important problem for many crops. Levels of above 10% CO2 effectively slow or stop the growth of numerous decay organisms (Brown, 1922). Low O2 has a very limited effect on decay organism activity or survival at levels above the fermentation threshold of most commodities. Strawberry, blueberry, blackberry, raspberry and cherry, they are examples that can be stored at CO2 atmosphere between 10 and 20%.

A negative plant responses to modified atmosphere packaging is when the respiration is reduced as O2 becomes limiting. Although there is a limit to which O2 can be reduced. The lower O2 limit is frequently considered to be the level of O2 that induces fermentation. However there are lower O2 levels that may confer benefits that outweigh the loss in flavor or other quality parameters. Ethanol, acetaldehyde, ethyl acetate and lactate are products of fermentation that can contribute to the development of off-flavors (Kays, 1997; Mattheis and Fellman, 2000).

Synthesis of aroma compounds are generally suppressed by high CO2 and low O2 levels, in part by their action on ethylene sensitivity, but also via action of O2 on oxidative processes, including respiration required for substrate production. But low O2 MAP may suppress aroma production so consumers perceive reduced quality upon opening the container.

## **7. Conclusions**

106 Polypropylene

The activation energy is a parameter that has been used to characterize plastic packaging. Knowledge of the activation energy of the breath of product and packaging serves as an important tool to predict the effects of temperature fluctuations on the concentration of

Some of the most important factors that affect shelf life of fresh horticultural products are ripening and/or senescence, decay, and cut surface browning. The effect of modified atmosphere on these factors has been studied for different crops. The application of MA to affect these limiting factors can be restricted for some crops by adverse and/or nonbeneficial physiological responses. Additionally, the good temperature management should

Low O2 and elevated CO2 concentrations can significantly reduce the rates of ripening and senescence primarily by reducing the synthesis and perception of ethylene (Burg and Burg, 1967; Abeles et al., 1992). Changes in respiration and starch, sugars, chlorophyll, and cell wall constituents during this period can be reduced, and in some cases nearly arrested, by

Chlorophyll loss, a desirable trait for many climacteric fruits, results in quality loss for many vegetables. Chlorophyll degradation during the senescence of green vegetables can be

Modified atmospheres are most effective at reducing ripening prior to the onset of ripening, rather than at a later stage. At the same time, packaged fruits and vegetables are usually intended for immediate consumption by the consumer and an unripe product is not immediately edible or is of reduced quality relative to the ripe product. Thus, the advantage of extend shelf-life by retarding ripening runs counter to the needs of the consumer when retail MAP systems are used. Nevertheless, MAP can reduce the rate of ripening of some

Decay control is a particularly important problem for many crops. Levels of above 10% CO2 effectively slow or stop the growth of numerous decay organisms (Brown, 1922). Low O2 has a very limited effect on decay organism activity or survival at levels above the fermentation threshold of most commodities. Strawberry, blueberry, blackberry, raspberry and cherry, they are examples that can be stored at CO2 atmosphere between 10 and 20%. A negative plant responses to modified atmosphere packaging is when the respiration is reduced as O2 becomes limiting. Although there is a limit to which O2 can be reduced. The lower O2 limit is frequently considered to be the level of O2 that induces fermentation. However there are lower O2 levels that may confer benefits that outweigh the loss in flavor or other quality parameters. Ethanol, acetaldehyde, ethyl acetate and lactate are products of fermentation that can contribute to the development of off-flavors (Kays, 1997; Mattheis and

Synthesis of aroma compounds are generally suppressed by high CO2 and low O2 levels, in part by their action on ethylene sensitivity, but also via action of O2 on oxidative processes, including respiration required for substrate production. But low O2 MAP may suppress aroma production so consumers perceive reduced quality upon opening the container.

commodities such as tomato even during its later stages (Yang and Chinnan, 1988).

eliminating ethylene action through the use of low O2/high CO2 atmospheres.

gases inside the package (Cameron et al., 1995).

be associated to by atmosphere modification.

reduced by low O2 and elevated CO2 (Ku and Wills, 1999).

**6. Plant responses of MAP**

Fellman, 2000).