Large collections of yeast were assembled, as the Centraalbureau voor Schimmelcultures (CBS) collection, in The Netherlands, and the Carlsberg collection, in Denmark. Manipula‐ tion of these strains to improve wine and beer properties has been performed in several ways, from spores manoeuvring and natural mutants' survey to genetic engineering (GE). A rather recent and extensive review in strategies for the improvement of *S. cerevisiae* industri‐ al strains can be found in [2]. As referred above, an efficient utilization of substrates by yeast during fermentation is extremely important for wine and beer industries. Such efficiency will yield higher amounts of by-products, as ethanol, and reduce the fermentation time. Fur‐ thermore, glucose repression on other sugars and consumption of unusual nitrogen sources

Yeast: World's Finest *Chef* http://dx.doi.org/10.5772/53156 531

The presence of glucose, even in small amounts, represses the simultaneous uptake and con‐ sumption of several sugars, namely maltose and galactose. Maltose (50%), maltotriose (15%) and sucrose (5%) are the main sugars in *wort* under glucose repression. Such repression leads to late fermentation of these sugars and slower fermentations, as their utilization is de‐ pendent on glucose depletion. This process is controlled at the transcriptional level, through the action of the proteins Mig1p, Ssn6p and Tup1p. Mig1p, a zinc finger protein, binds to specific sequences in the promoter region of the glucose-repressed genes and recruits the SSN6-TUP1 complex, the responsible for the actual repression [49]. Mig1p binding sites were found in genes associated with the utilization of sucrose (*SUC*2), maltose (*MALR*, *MALS* and *MALT*) and galactose (*GAL*1-5) [50]. Therefore, *MIG1* presents itself as a potential

Conversely, in sucrose metabolism, glucose repression addresses the sucrose conversion in fructose and glucose under the action of Suc2p. Studies showed that the disruption of *MIG*1 lessen the glucose repression on the transcription of this excreted invertase in both lab and industrial strains. Therefore, the lag in sucrose utilization was greatly diminished. Besides Mig1p, another zinc finger protein, Mig2p, was associated with glucose repression of *SUC*2 [51]. The interruption of both *MIG*1 and *MIG*2, in *S. cerevisiae* strains led a high sucrose me‐

Maltose metabolism is more complex than sucrose, as it responds to both glucose repression and maltose induction. Maltose induction is under the influence of the locus *MAL*, a closely integrated group of genes. This sugar presence induces *MALR*, a transcription factor, which in turn will induce *MALT*, coding for a maltose permease, and *MALS*, coding for a maltase [30]. Up to 5 different *loci* have been detected in *S. cerevisiae* industrial strains; still haploid lab strains present a single *locus*. In both situations these *loci* are under repression of Mig1p [53]. However, disruption of *MIG*1 in industrial strains only alleviated the sucrose metabo‐ lism [50], but didn't cause any effect regarding maltose metabolism. Even though, in haploid lab strains *MIG*1 disruption lifted the glucose repression; the same has not happen in the polyploid strains, presenting multiple *loci*. Complex regulation between the different genes

Finally, maltotriose, a glucose tri-saccharide, is the second most abundant sugar in *wort* (15%). This is under similar regulation by the presence of glucose and maltose, therefore most studies have focused in an efficient uptake of this carbohydrate [54]. Those works

are vital research areas [30].

target to improve yeast sugar consumption.

tabolism in the presence of high glucose concentrations [52].

must be under way and most probably not solely controlled by Mig1p [53].

Ethanol is one of the most important by-products of beer fermentation. Nevertheless, it rep‐ resents an important stressor for yeast cells due to its high toxicity. Ethanol concentration can reach 10% in higher gravity fermentations, and acts especially upon biological mem‐ branes [35]. Reports showed ethanol effects in growth inhibition [45], lipid modification and loss of proton motive force across the membrane and increased membrane permeability/ fluidity [46]. Yet, cells exposed to oxygen, with high levels of sterols in membranes, and ade‐ quate levels of nutrients, amino acids and trace elements in the fermentation broth are able to respond efficiently to such effects [35].

Nutritional stress occurs at the end of fermentation and cells enter stationary phase. This oc‐ curs because fermentable carbon sources tend to be depleted, and cells have to change their metabolism from fermentative to respiratory (explained in section 1), entering in a quiescent state [30]. Such phenomenon induces flocculation, a cell-cell interaction process dependent of lectins and calcium that promotes sedimentation. Flocculation in turn is influenced by several other factors besides nutrient depletion. Reports showed the influence of ethanol content, calcium concentration, pH changes, oxygen concentration and temperature [47]. The onset of flocculation is an important area of interest in brewing. If flocculation occurs to soon, stuck fermentation may occur, which results in a high sugar and low ethanol content. If, on the other hand, happens in a later stage, it has a high impact in beer filtration as most cells tend to be kept in suspension.

Fermentation is the most yeast-dependent phase of these alcoholic beverages production, but yeast also interferes with others proceedings. The metabolic fitness of the starter culture, the storage and maintenance of both dried and fresh yeasts, and the storage of the products submit yeast to different conditions to which they have to respond/adapt. To obtain detailed information on such processes please see reviews [35] and [43].

#### **2.2. Old beverages, new solutions**

Wine and beer industrial production led to a demand for better and more efficient yeast. Yeasts with improved utilization of substrates, carbohydrates and nitrogen, and consistent flocculent behaviour, as well as high fermentative capacity and high ethanol production are the industry goal. Enhancing beer and wine flavour through modification of by-products formation is another field of intensive research [30, 39]. As it is the improvement of the fer‐ mentation process, through encapsulation/immobilization of yeast [48].

Large collections of yeast were assembled, as the Centraalbureau voor Schimmelcultures (CBS) collection, in The Netherlands, and the Carlsberg collection, in Denmark. Manipula‐ tion of these strains to improve wine and beer properties has been performed in several ways, from spores manoeuvring and natural mutants' survey to genetic engineering (GE). A rather recent and extensive review in strategies for the improvement of *S. cerevisiae* industri‐ al strains can be found in [2]. As referred above, an efficient utilization of substrates by yeast during fermentation is extremely important for wine and beer industries. Such efficiency will yield higher amounts of by-products, as ethanol, and reduce the fermentation time. Fur‐ thermore, glucose repression on other sugars and consumption of unusual nitrogen sources are vital research areas [30].

beers are usually stored from several days to weeks, lagering, solely to remove diacetyl, an off-flavour causing metabolite. This time consuming maturation phase consists in a second fermentation at low temperature to eliminate the butter-like flavour caused by this vicinal diketone. Studies are being conducted in order to minimize this metabolite formation and reduce the maturation time [30]. Sulphur containing compounds are other family of byproducts receiving great attention. Such group comprises sulphite, sulphide and dimethyl sulphide, and while sulphite is a beneficial and flavour stabilizing metabolite, the remaining compounds are responsible for off-flavours. The equilibrium of such compounds formation

Ethanol is one of the most important by-products of beer fermentation. Nevertheless, it rep‐ resents an important stressor for yeast cells due to its high toxicity. Ethanol concentration can reach 10% in higher gravity fermentations, and acts especially upon biological mem‐ branes [35]. Reports showed ethanol effects in growth inhibition [45], lipid modification and loss of proton motive force across the membrane and increased membrane permeability/ fluidity [46]. Yet, cells exposed to oxygen, with high levels of sterols in membranes, and ade‐ quate levels of nutrients, amino acids and trace elements in the fermentation broth are able

Nutritional stress occurs at the end of fermentation and cells enter stationary phase. This oc‐ curs because fermentable carbon sources tend to be depleted, and cells have to change their metabolism from fermentative to respiratory (explained in section 1), entering in a quiescent state [30]. Such phenomenon induces flocculation, a cell-cell interaction process dependent of lectins and calcium that promotes sedimentation. Flocculation in turn is influenced by several other factors besides nutrient depletion. Reports showed the influence of ethanol content, calcium concentration, pH changes, oxygen concentration and temperature [47]. The onset of flocculation is an important area of interest in brewing. If flocculation occurs to soon, stuck fermentation may occur, which results in a high sugar and low ethanol content. If, on the other hand, happens in a later stage, it has a high impact in beer filtration as most

Fermentation is the most yeast-dependent phase of these alcoholic beverages production, but yeast also interferes with others proceedings. The metabolic fitness of the starter culture, the storage and maintenance of both dried and fresh yeasts, and the storage of the products submit yeast to different conditions to which they have to respond/adapt. To obtain detailed

Wine and beer industrial production led to a demand for better and more efficient yeast. Yeasts with improved utilization of substrates, carbohydrates and nitrogen, and consistent flocculent behaviour, as well as high fermentative capacity and high ethanol production are the industry goal. Enhancing beer and wine flavour through modification of by-products formation is another field of intensive research [30, 39]. As it is the improvement of the fer‐

could lead to better wine and beer and shorter fermentations [44].

information on such processes please see reviews [35] and [43].

mentation process, through encapsulation/immobilization of yeast [48].

to respond efficiently to such effects [35].

530 Food Industry

cells tend to be kept in suspension.

**2.2. Old beverages, new solutions**

The presence of glucose, even in small amounts, represses the simultaneous uptake and con‐ sumption of several sugars, namely maltose and galactose. Maltose (50%), maltotriose (15%) and sucrose (5%) are the main sugars in *wort* under glucose repression. Such repression leads to late fermentation of these sugars and slower fermentations, as their utilization is de‐ pendent on glucose depletion. This process is controlled at the transcriptional level, through the action of the proteins Mig1p, Ssn6p and Tup1p. Mig1p, a zinc finger protein, binds to specific sequences in the promoter region of the glucose-repressed genes and recruits the SSN6-TUP1 complex, the responsible for the actual repression [49]. Mig1p binding sites were found in genes associated with the utilization of sucrose (*SUC*2), maltose (*MALR*, *MALS* and *MALT*) and galactose (*GAL*1-5) [50]. Therefore, *MIG1* presents itself as a potential target to improve yeast sugar consumption.

Conversely, in sucrose metabolism, glucose repression addresses the sucrose conversion in fructose and glucose under the action of Suc2p. Studies showed that the disruption of *MIG*1 lessen the glucose repression on the transcription of this excreted invertase in both lab and industrial strains. Therefore, the lag in sucrose utilization was greatly diminished. Besides Mig1p, another zinc finger protein, Mig2p, was associated with glucose repression of *SUC*2 [51]. The interruption of both *MIG*1 and *MIG*2, in *S. cerevisiae* strains led a high sucrose me‐ tabolism in the presence of high glucose concentrations [52].

Maltose metabolism is more complex than sucrose, as it responds to both glucose repression and maltose induction. Maltose induction is under the influence of the locus *MAL*, a closely integrated group of genes. This sugar presence induces *MALR*, a transcription factor, which in turn will induce *MALT*, coding for a maltose permease, and *MALS*, coding for a maltase [30]. Up to 5 different *loci* have been detected in *S. cerevisiae* industrial strains; still haploid lab strains present a single *locus*. In both situations these *loci* are under repression of Mig1p [53]. However, disruption of *MIG*1 in industrial strains only alleviated the sucrose metabo‐ lism [50], but didn't cause any effect regarding maltose metabolism. Even though, in haploid lab strains *MIG*1 disruption lifted the glucose repression; the same has not happen in the polyploid strains, presenting multiple *loci*. Complex regulation between the different genes must be under way and most probably not solely controlled by Mig1p [53].

Finally, maltotriose, a glucose tri-saccharide, is the second most abundant sugar in *wort* (15%). This is under similar regulation by the presence of glucose and maltose, therefore most studies have focused in an efficient uptake of this carbohydrate [54]. Those works showed that overexpression of maltotriose transporters lead to positive effects on its metab‐ olism [54, 55].

tolactate decarboxylase (ALDC) in yeast is the main approach to reduce the amounts of this compound. ALDC catalyses the reaction of α-acetolactate to acetoin, preventing the forma‐ tion of diacetyl. However, after heterologous expression of ALDC, the yeast became auxo‐ trophic for some amino acids and the growth rate was very low in *wort*. An alternative approach was the interruption of *ILV*2, encoding acetolactate synthase. Such strategy also resulted in an auxotrophic strain with slow growth. The search for natural mutants in *ILV*2

Yeast: World's Finest *Chef* http://dx.doi.org/10.5772/53156 533

Improvement of yeast to render fermentations faster and cheaper is an industry goal, but the enhancing of the fermentation process itself is another alternative. The fed-batch technology has already proved its benefits [38], and improvements of such process with yeast immobili‐ zation/encapsulation are now under the spotlight. This results in much faster fermentation rates as compared to the existing free cell fermentations. However, it has some disadvantag‐ es, such as: i) complexity of production process including the choice of the suitable carrier materials, ii) bioreactors design, iii) fine-tuning of the flavour formation during fermentation

The process of bread making relies on the fermentation carried out by a mixture of yeast and bacteria. Even when all this was unknown and the flour leavening seen as "magic", bread was already produced and extensively consumed. On those ancient times, the leavening re‐ sulted presumably due to the action (fermentation) of the natural microbial contaminants of flour or dough ingredients. This was obviously not a controlled process, yet with the prac‐ tice of maintaining a fresh inoculum from one preparation to the next, promoted the selec‐ tion of yeast and bacteria biodiversity. Nowadays, some types of bread are still prepared in this fashion, sourdoughs are one example (for a review see [2]), but the baking industry moved for the use of commercially baker's yeast, typically the strain *S. cerevisiae*, for the bread production. And, while the flour types, geographical origin and mixtures introduce organoleptic differences in bread, the globalization of commercial baker's yeast market de‐

Commercial baker's yeast is produced in several forms in order to meet specific require‐ ments of climate, technology, methodology, transportation, storage and final product. As with all biotechnology processes, this is in constant development/undergoing research not only to optimize the process technology and its components, but as to produce faster grow‐

Molasses (beet and cane molasses), the common carbon and energy source used in the production of baker's yeast, is a by-product of sugar refining industries, therefore cheap‐ er than the formerly used cereals grain. Furthermore the sugars present on those molass‐ es (around 50%), consisting on a mixture of sucrose, fructose and glucose, are ready to be

with an appropriated growth rate is now the major strategy [30].

processes, and iv) cost constraints [59].

**3. Baker's yeast – Magic on bread making**

creased worldwide bread diversity (for a review see [2]).

**3.1. Commercial baker's yeast production – The break of spell**

ing strains with the characteristics to deliver better quality end products.

In winemaking and brewing, where flavour has such importance, amino acids metabolism has a notorious place. As said, amino acids are involved in formation of higher alcohols and esters that significantly contribute to beer and wine flavour. Since yeast cannot hydrolyse *must* and *wort* proteins, it depends on the available ammonium and amino acids in solution [11, 30]. However, the predominant amino acid in both *must* and *wort*, proline, is the less as‐ similated [40]. As such, improvements in yeast ability to uptake this amino acid has been attempted. Efficient proline uptake was reported in lager beer yeast expressing a mutagen‐ ized proline permease, Put4p. The site-directed mutagenesis stabilized the permease and en‐ hanced amino acid utilization without affecting the beer quality [56]. The study of the same problematic in winemaking led to the disruption of *URE*1, a repressor of permease encoding *PUT*1 and pyrroline-5-carboxylate dehydrogenase *PUT*2, with significant improvements in fermentation rate and vigour described [57].

Flocculation is a phenotype of industrial interest. It facilitates the filtration process in the end of fermentation, saving both time and money. In the case of brewing, it also serves the cropping (recover of part of the yeast population of the fermentation to pitch the next). Floc‐ culation is a reversible aggregation of cells, where lectins recognize sugar residues in neigh‐ bour cells. Two industrially relevant flocculation phenotypes are well-known, Flo1 and NewFlo. Both are under the control of *FLO* genes, Flo1 phenotype is repressed by mannose and NewFlo by mannose, glucose and sucrose. Almost every industrial strain is NewFlo, as‐ sociated with *FLO*10 [30]. The main approach to improve these phenotypes is to put *FLO* genes under a promoter active only in stationary phase. Promoters of *HSP26* and *HSP30* were proven as the most suitable for induction at this late growth phase in lab strains [30].

The control of by-products production in order to improve wine and beer organoleptic properties is an expanding research area. The production of glycerol, to improve wine and beer's fullness, as well as sulphite, to improve stability, and the reduction in diacetyl and sulphide content are the main targets. Glycerol, as the second fermentation metabolite, is rather important to wine and beer; the increase of its concentration to improve these bever‐ ages sensory character is an active field. Overexpression of *GPD*1, encoding glycerol-3-pho‐ phate dehydrogenase, is the main approach. However, this change resulted in a redox imbalance with increased production of unwanted metabolites [39]. This point has been fully discussed in [2].

The presence of sulphite, an antioxidant and flavour stabilizer, and reduction of off-flavour producing sulphide is another important problem addressed by the industry. Both these goals can be achieved at the same time with the directed mutagenesis of NADPH-dependent sulphite reductase, an important enzyme in sulphur–containing amino acids synthesis. This strategy lowered this enzyme activity and increased the amount of sulphite in wine while reducing the sulphide presence in wine [58].

The reduction of diacetyl has special importance, as the maturation time (lagering) is direct‐ ly dependent on this compound concentration. The expression of the bacterial enzyme ace‐ tolactate decarboxylase (ALDC) in yeast is the main approach to reduce the amounts of this compound. ALDC catalyses the reaction of α-acetolactate to acetoin, preventing the forma‐ tion of diacetyl. However, after heterologous expression of ALDC, the yeast became auxo‐ trophic for some amino acids and the growth rate was very low in *wort*. An alternative approach was the interruption of *ILV*2, encoding acetolactate synthase. Such strategy also resulted in an auxotrophic strain with slow growth. The search for natural mutants in *ILV*2 with an appropriated growth rate is now the major strategy [30].

Improvement of yeast to render fermentations faster and cheaper is an industry goal, but the enhancing of the fermentation process itself is another alternative. The fed-batch technology has already proved its benefits [38], and improvements of such process with yeast immobili‐ zation/encapsulation are now under the spotlight. This results in much faster fermentation rates as compared to the existing free cell fermentations. However, it has some disadvantag‐ es, such as: i) complexity of production process including the choice of the suitable carrier materials, ii) bioreactors design, iii) fine-tuning of the flavour formation during fermentation processes, and iv) cost constraints [59].

## **3. Baker's yeast – Magic on bread making**

showed that overexpression of maltotriose transporters lead to positive effects on its metab‐

In winemaking and brewing, where flavour has such importance, amino acids metabolism has a notorious place. As said, amino acids are involved in formation of higher alcohols and esters that significantly contribute to beer and wine flavour. Since yeast cannot hydrolyse *must* and *wort* proteins, it depends on the available ammonium and amino acids in solution [11, 30]. However, the predominant amino acid in both *must* and *wort*, proline, is the less as‐ similated [40]. As such, improvements in yeast ability to uptake this amino acid has been attempted. Efficient proline uptake was reported in lager beer yeast expressing a mutagen‐ ized proline permease, Put4p. The site-directed mutagenesis stabilized the permease and en‐ hanced amino acid utilization without affecting the beer quality [56]. The study of the same problematic in winemaking led to the disruption of *URE*1, a repressor of permease encoding *PUT*1 and pyrroline-5-carboxylate dehydrogenase *PUT*2, with significant improvements in

Flocculation is a phenotype of industrial interest. It facilitates the filtration process in the end of fermentation, saving both time and money. In the case of brewing, it also serves the cropping (recover of part of the yeast population of the fermentation to pitch the next). Floc‐ culation is a reversible aggregation of cells, where lectins recognize sugar residues in neigh‐ bour cells. Two industrially relevant flocculation phenotypes are well-known, Flo1 and NewFlo. Both are under the control of *FLO* genes, Flo1 phenotype is repressed by mannose and NewFlo by mannose, glucose and sucrose. Almost every industrial strain is NewFlo, as‐ sociated with *FLO*10 [30]. The main approach to improve these phenotypes is to put *FLO* genes under a promoter active only in stationary phase. Promoters of *HSP26* and *HSP30* were proven as the most suitable for induction at this late growth phase in lab strains [30].

The control of by-products production in order to improve wine and beer organoleptic properties is an expanding research area. The production of glycerol, to improve wine and beer's fullness, as well as sulphite, to improve stability, and the reduction in diacetyl and sulphide content are the main targets. Glycerol, as the second fermentation metabolite, is rather important to wine and beer; the increase of its concentration to improve these bever‐ ages sensory character is an active field. Overexpression of *GPD*1, encoding glycerol-3-pho‐ phate dehydrogenase, is the main approach. However, this change resulted in a redox imbalance with increased production of unwanted metabolites [39]. This point has been

The presence of sulphite, an antioxidant and flavour stabilizer, and reduction of off-flavour producing sulphide is another important problem addressed by the industry. Both these goals can be achieved at the same time with the directed mutagenesis of NADPH-dependent sulphite reductase, an important enzyme in sulphur–containing amino acids synthesis. This strategy lowered this enzyme activity and increased the amount of sulphite in wine while

The reduction of diacetyl has special importance, as the maturation time (lagering) is direct‐ ly dependent on this compound concentration. The expression of the bacterial enzyme ace‐

olism [54, 55].

532 Food Industry

fermentation rate and vigour described [57].

fully discussed in [2].

reducing the sulphide presence in wine [58].

The process of bread making relies on the fermentation carried out by a mixture of yeast and bacteria. Even when all this was unknown and the flour leavening seen as "magic", bread was already produced and extensively consumed. On those ancient times, the leavening re‐ sulted presumably due to the action (fermentation) of the natural microbial contaminants of flour or dough ingredients. This was obviously not a controlled process, yet with the prac‐ tice of maintaining a fresh inoculum from one preparation to the next, promoted the selec‐ tion of yeast and bacteria biodiversity. Nowadays, some types of bread are still prepared in this fashion, sourdoughs are one example (for a review see [2]), but the baking industry moved for the use of commercially baker's yeast, typically the strain *S. cerevisiae*, for the bread production. And, while the flour types, geographical origin and mixtures introduce organoleptic differences in bread, the globalization of commercial baker's yeast market de‐ creased worldwide bread diversity (for a review see [2]).

#### **3.1. Commercial baker's yeast production – The break of spell**

Commercial baker's yeast is produced in several forms in order to meet specific require‐ ments of climate, technology, methodology, transportation, storage and final product. As with all biotechnology processes, this is in constant development/undergoing research not only to optimize the process technology and its components, but as to produce faster grow‐ ing strains with the characteristics to deliver better quality end products.

Molasses (beet and cane molasses), the common carbon and energy source used in the production of baker's yeast, is a by-product of sugar refining industries, therefore cheap‐ er than the formerly used cereals grain. Furthermore the sugars present on those molass‐ es (around 50%), consisting on a mixture of sucrose, fructose and glucose, are ready to be fermented by the yeast. In order to obtain the proper broth for the optimum yeast bio‐ mass yield; the mixture of molasses has to be supplemented with nitrogen sources, miner‐ als, salts and vitamins [60, 61].

ed, with incubation at optimal temperatures, the CO2 starts to saturate the liquid phase of the dough and starts to accumulate in the bubble *nuclei* [66]. This leads to dough rising pro‐ vided that a mature gluten network, capable of ensure the dough foam-like structure, is formed. The amount of time such process occurs will influence dough gumminess and rheology, as well as crust colour, crumb texture, and firmness of the bread (reviewed by [2, 3]). The amount of sugars present in the dough that are actually fermented, as well as the efficient secretion of enzymes as invertase, responsible for the conversion of sucrose to glu‐ cose and fructose, has a great impact in the flavour characteristics of the bread. The action of several enzymes, namely proteases, lecithinases, lipases α-glucosidase and β-fructosidase, leads to different utilization of the dough substrates. In bread making, the flavour is also greatly influenced by the metabolic by-products of the yeast fermentation, and while the most important by-product of yeast metabolism is certainly the CO2, the production of me‐ tabolites such as alcohols, esters, and carbonyl compounds have also a deep impact. More than 300 volatile compounds associated with bread's flavour and aroma, are produced by yeast. Although, some are dependent more on the substrates, the vast majority of such com‐

Yeast: World's Finest *Chef* http://dx.doi.org/10.5772/53156 535

pounds are yeast dependent, introducing an important variability to bread [67].

year [2] as well as on [3, 68].

**4. Yeast à la Carte**

metals [70, 71].

**4.1. Yeast treats for animals**

As mentioned, the common procedure of bread making today, at least in developed coun‐ tries, consists of using this commercial baker's yeast. Its quality/individuality depends on storage stability, osmotolerance and freeze-thaw resistance. Considerable efforts have been made to obtain the Idol Yeast, including evolutionary engineering, genetic engineering (mainly to provide yeast with high capacity to tolerate freeze-thaw treatments). Yet, there is still considerable space for improvement. Those several strategies to achieve the Idol Yeast has been thoroughly revised and discussed in a previous work from the beginning of this

Fresh *S. cerevisiae* consists of approximately 30–33% of dry materials, 6.5–9.3% of nitrogen, 40.6–58.0% of proteins, 35.0–45.0% of carbohydrates, 4.0–6.0% of lipids, 5.0–7.5% of minerals and various amounts of vitamins, depending on its growth conditions [69]. So, today yeasts are acquiring increasingly more attention for other uses, besides the production of alcoholic beverages and the baling industry. The products of modern yeast biotechnology form the backbone of many commercially important sectors, including functional foods (for animals, fish and humans), health food supplements, including additives, conditioners and flavour‐ ing agents, as pharmaceutical products, for the production of microbiology media and ex‐ tracts, as well as livestock feed or even as agents of detoxifying effluents containing heavy

The pioneering research conducted almost a century ago by Max Delbrück and his collea‐ gues was the first to highlight the value of surplus brewer's yeast as a feeding supplement

After the preparation and sterilization of the broth, the production of baker yeast can take place. It begins by the inoculation of a small closed test flask containing the prepared steri‐ lized broth with a pure yeast culture. The growth is allowed and careful screened, and when the culture reaches an elevated density, it is transferred to larger vessels and supplied with more broth, fed-batch reactors. This scale-up process continues until a desirable biomass quantity is attained, the so-called commercial starter, able to inoculate industrial fermenters/ reactors, which production ranges from 40,000 to 200,000L [62].

The entire fermentation process of baker's yeast has to be directed towards maximum bio‐ mass production; by-products such as ethanol are not desired. As we saw in section 1.1.1, in anaerobic dissimilation of sugars (alcoholic fermentation) the ATP yield is quite low com‐ paring with respiratory dissimilation, affecting drastically the biomass yield. The way to avoid anaerobic ethanol production is the use of the mentioned fed-batch reactors, in which is possible to control the specific growth rate and sugar concentration by controlling the fed of reactors with fresh broth [63].

Nowadays, during the industrial large reactors the addition of nutrients and regulation of pH, temperature and airflow are carefully monitored and controlled by computer systems during the entire production process. In this way, the tones of baker's yeast obtained in the end of the fermentation have the same quality/characteristics/properties as the original pure yeast culture that started the process. These tones of yeast are suspended in a large amount of water, resulting in a creamy suspension of active yeast, being necessary the so-called **downstream processes** to obtain the concentrated yeast [64, 65]. At the end of the fermenta‐ tion, the yeast culture is concentrated using a series of combined centrifugation and washing steps, into a yeast cream with concentration of approximately 20%. The yeast is then cooled to approximately 4°C, and stored. It can be sold in this form – **Cream Yeast**- however is quite expensive due to the manipulations required because of high content in water. Cream yeast can be further processed, compressed or dried originating the **Granular Yeast** or **In‐ stant Dried Yeast**, if then converted in small granules, or **Cake Yeast** or **Active Dry Yeast**, if as an alternative the dried yeast is extruded or cut into blocks/cakes. All these yeast types are then packaged, typically vacuum packed to reduce the risk of contamination, and dis‐ tributed to wholesalers or traders. The shelf life of Active Dry/Cake Yeast and Instant Dry/ Granular Yeast at ambient temperature is 1 to 2 years.

#### **3.2. Idol baker's yeast**

Yeast has a significant role on bread making, greatly influencing the final product proper‐ ties. The most important contribution is in the leavening phase; after the dough has been kneaded and the gluten network start to develop, yeast starts to consume the available fer‐ mentable sugars and to produce ethanol and CO2, as mentioned in section 1. As fermenta‐ tion occurs, the dough is gradually depleted of O2 present in the air bubbles trapped in the dough, leaving small bubble *nuclei* full of N2. As the metabolism is more and more stimulat‐ ed, with incubation at optimal temperatures, the CO2 starts to saturate the liquid phase of the dough and starts to accumulate in the bubble *nuclei* [66]. This leads to dough rising pro‐ vided that a mature gluten network, capable of ensure the dough foam-like structure, is formed. The amount of time such process occurs will influence dough gumminess and rheology, as well as crust colour, crumb texture, and firmness of the bread (reviewed by [2, 3]). The amount of sugars present in the dough that are actually fermented, as well as the efficient secretion of enzymes as invertase, responsible for the conversion of sucrose to glu‐ cose and fructose, has a great impact in the flavour characteristics of the bread. The action of several enzymes, namely proteases, lecithinases, lipases α-glucosidase and β-fructosidase, leads to different utilization of the dough substrates. In bread making, the flavour is also greatly influenced by the metabolic by-products of the yeast fermentation, and while the most important by-product of yeast metabolism is certainly the CO2, the production of me‐ tabolites such as alcohols, esters, and carbonyl compounds have also a deep impact. More than 300 volatile compounds associated with bread's flavour and aroma, are produced by yeast. Although, some are dependent more on the substrates, the vast majority of such com‐ pounds are yeast dependent, introducing an important variability to bread [67].

As mentioned, the common procedure of bread making today, at least in developed coun‐ tries, consists of using this commercial baker's yeast. Its quality/individuality depends on storage stability, osmotolerance and freeze-thaw resistance. Considerable efforts have been made to obtain the Idol Yeast, including evolutionary engineering, genetic engineering (mainly to provide yeast with high capacity to tolerate freeze-thaw treatments). Yet, there is still considerable space for improvement. Those several strategies to achieve the Idol Yeast has been thoroughly revised and discussed in a previous work from the beginning of this year [2] as well as on [3, 68].

## **4. Yeast à la Carte**

fermented by the yeast. In order to obtain the proper broth for the optimum yeast bio‐ mass yield; the mixture of molasses has to be supplemented with nitrogen sources, miner‐

After the preparation and sterilization of the broth, the production of baker yeast can take place. It begins by the inoculation of a small closed test flask containing the prepared steri‐ lized broth with a pure yeast culture. The growth is allowed and careful screened, and when the culture reaches an elevated density, it is transferred to larger vessels and supplied with more broth, fed-batch reactors. This scale-up process continues until a desirable biomass quantity is attained, the so-called commercial starter, able to inoculate industrial fermenters/

The entire fermentation process of baker's yeast has to be directed towards maximum bio‐ mass production; by-products such as ethanol are not desired. As we saw in section 1.1.1, in anaerobic dissimilation of sugars (alcoholic fermentation) the ATP yield is quite low com‐ paring with respiratory dissimilation, affecting drastically the biomass yield. The way to avoid anaerobic ethanol production is the use of the mentioned fed-batch reactors, in which is possible to control the specific growth rate and sugar concentration by controlling the fed

Nowadays, during the industrial large reactors the addition of nutrients and regulation of pH, temperature and airflow are carefully monitored and controlled by computer systems during the entire production process. In this way, the tones of baker's yeast obtained in the end of the fermentation have the same quality/characteristics/properties as the original pure yeast culture that started the process. These tones of yeast are suspended in a large amount of water, resulting in a creamy suspension of active yeast, being necessary the so-called **downstream processes** to obtain the concentrated yeast [64, 65]. At the end of the fermenta‐ tion, the yeast culture is concentrated using a series of combined centrifugation and washing steps, into a yeast cream with concentration of approximately 20%. The yeast is then cooled to approximately 4°C, and stored. It can be sold in this form – **Cream Yeast**- however is quite expensive due to the manipulations required because of high content in water. Cream yeast can be further processed, compressed or dried originating the **Granular Yeast** or **In‐ stant Dried Yeast**, if then converted in small granules, or **Cake Yeast** or **Active Dry Yeast**, if as an alternative the dried yeast is extruded or cut into blocks/cakes. All these yeast types are then packaged, typically vacuum packed to reduce the risk of contamination, and dis‐ tributed to wholesalers or traders. The shelf life of Active Dry/Cake Yeast and Instant Dry/

Yeast has a significant role on bread making, greatly influencing the final product proper‐ ties. The most important contribution is in the leavening phase; after the dough has been kneaded and the gluten network start to develop, yeast starts to consume the available fer‐ mentable sugars and to produce ethanol and CO2, as mentioned in section 1. As fermenta‐ tion occurs, the dough is gradually depleted of O2 present in the air bubbles trapped in the dough, leaving small bubble *nuclei* full of N2. As the metabolism is more and more stimulat‐

reactors, which production ranges from 40,000 to 200,000L [62].

Granular Yeast at ambient temperature is 1 to 2 years.

als, salts and vitamins [60, 61].

534 Food Industry

of reactors with fresh broth [63].

**3.2. Idol baker's yeast**

Fresh *S. cerevisiae* consists of approximately 30–33% of dry materials, 6.5–9.3% of nitrogen, 40.6–58.0% of proteins, 35.0–45.0% of carbohydrates, 4.0–6.0% of lipids, 5.0–7.5% of minerals and various amounts of vitamins, depending on its growth conditions [69]. So, today yeasts are acquiring increasingly more attention for other uses, besides the production of alcoholic beverages and the baling industry. The products of modern yeast biotechnology form the backbone of many commercially important sectors, including functional foods (for animals, fish and humans), health food supplements, including additives, conditioners and flavour‐ ing agents, as pharmaceutical products, for the production of microbiology media and ex‐ tracts, as well as livestock feed or even as agents of detoxifying effluents containing heavy metals [70, 71].

#### **4.1. Yeast treats for animals**

The pioneering research conducted almost a century ago by Max Delbrück and his collea‐ gues was the first to highlight the value of surplus brewer's yeast as a feeding supplement for animals [72]. Yeasts have been fed to animals for more than a hundred years, either in the form of yeast fermented mash produced on the farm, yeast by-products from breweries or distilleries, or commercial yeast products specifically produced for animal feeding. In ani‐ mals, including pets, this practice is used to compensate for the amino acid and vitamin de‐ ficiencies of cereals [73, 74], and in fish as a substitute for other ingredients [71].

digestion of the fibrous and cellulolytic portion of the diet, which leads to a greater intake of

Yeast: World's Finest *Chef* http://dx.doi.org/10.5772/53156 537

Dried yeast was used traditionally in poultry diets in the past as a source of aminoacids and micronutrients, and though the broiler growth was improving this practice was largely dis‐ continued for economic reasons [77]. On the other hand, brewer's yeast appears to be espe‐ cially beneficial for breeder turkeys and laying hens [85]. Reproductive improvements are attributed to the high level of dietary biotin and selenium in yeast, which is more beneficial than inorganic selenium added to poultry diets [86] and it contributes for the prevention of biotin deficiency in poultry diets, which may result in reduced feed conversion, low egg production, and poor hatchability [87]. Brewer's yeast is also very rich in folic acid, an im‐

Brewer's yeast has been recognized to have potential as well as a substitute for live food in the production of certain fish or as a potential replacement for fishmeal [88-90]. In addition, it has low content in phosphorous, meaning less water and environmental contamination than common fish meal and other plant-based alternate protein sources [91]. Multiple stud‐ ies have demonstrated the immunostimulant properties of yeasts, such as their ability to en‐ hance non-specific immune activity [92]. That reaction can be related to β-glucans, nucleic acids as well as mannan oligosaccharides [93]. Brewer's yeast may serve as an excellent health promoter for fish culture as even when administered for relatively long periods is able to enhance immune responses as well as growth of various fish species, without caus‐ ing immunosuppression [94, 95]. Furthermore, the relative high levels of nucleic acid nitro‐ gen present (mostly in the form of RNA) that in humans and most monogastric animals can became toxic if taken in excess, as the capacity of excretion of the uric acid formed is limited

In a world of rapidly increasing population and low agricultural production, yeasts are rela‐ tively cheap and easily produced on an industrial scale representing a sustainable alternate protein source to cover the population nutritional demands. The first time that yeast was cultivated in large scale for human nutritional use was in Germany during both World Wars [72]. The yeasts *S. cerevisiae* as baker yeast, *Candida utilis* as torula yeast, and *Kluyveromyces fragilis* as whey yeast, when produced on suitable, food grade substrates (*e.g.*, sugars, etha‐ nol, and lactose), are permitted in many foods around the world [70]. Besides the alcoholic beverages and baking products referred above, yeast are used in the health food industry; as additives, conditioners, and flavouring agents; as sources of high nutritional value proteins, enzymes, nucleic acids, nucleotides, and cell wall polysaccharides [98] as well as for the pro‐ duction of food-grade yeast extracts and autolysates [69, 99]. Yeast extract from dried brew‐ er's yeast cells can be used by enzymatic treatment in a wide variety of foods (*e.g.*, meat products, sauces and gravies, soups, chips and crackers) as flavours enhancers or potentia‐ tors [73, 100]. β-Glucan obtained from brewer's yeast can be used in food products as a thickening, water-holding, or oil-binding agent and emulsifying stabilizer [101]. The probi‐ otic activity is an additional role of some yeast that is attracting increasing interest [102].

[96], in fish does not happen due to their very active liver uricase [97].

food and better performance [83, 84].

portant vitamin for turkeys [73].

**4.2. Human little treats, big benefits**

Brewer's yeast biomass, as described above, which results from the cultivation of *S. cerevisiae* on malted barley, separated after the *wort* fermentation, debittered and then dried, is the second major by-product from brewing industry, just after the brewer spent grain [73]. This biomass is an excellent source of proteins, peptides and amino acids, vitamins (especially of B-group: B1, B2, PP, B5, B6, B8, B12), minerals and trace elements (calcium, phosphorus, po‐ tassium, magnesium, copper, iron, zinc, manganese, chromium, selenium), carbohydrates (glucans and mannans), as well as phospholipids [75]. The winemaking industry also gener‐ ates a huge amount of microbial biomass - **leeds**. Yet, this incorporates the yeasts (that die due to nutrient depletion) but also other microorganisms, suspended solids, colloids, and organic matter, and have been shown to display quite low nutritional value to be considered for use as a supplement in animal feed [76].

Those yeast used for monogastrics food or feeding rations is generally inactivated because feeding of live yeast might cause avitaminosis due to the depletion of B-vitamins in the in‐ testine [77]. They can also cause adverse fermentation in the digestive tract of swine leading to diarrhoea and bloating [75]. Yeasts can be killed through application of heat or using chemicals. High temperature destroys the yeast membrane, but does not necessarily inacti‐ vate all yeast enzymes, unless quite elevated temperatures are applied. Alternatively, there are the chemical treatments with propionic acid or formic acid, which also act as a preserva‐ tives for yeast, and contribute to the feed value of the yeast [73].

Yeasts have been used in diets of numerous species with varying levels of success. Yeast for swines is sold for feed applications as wet slurry, as dried brewer's yeast, or in mixtures with other brewery by-products [73]. It is ideal for their feed as a good protein source, it contains most of the essential amino acids in adequate quantities, and numerous vitamins, selenium, copper, and phosphorus. Selenium concentrations are much higher in yeast than in soybean meal, and deficiency of this compound in the swine's alimentation has been the cause of high‐ er swine mortality [78, 79]. Additionally, dried brewer's yeast contains mannan oligosacchar‐ ides, which have been reported to increase the growth performance and intestinal health of pigs [80]. Benefits have been described as well for nursing and weanling pigs [81].

Either live or inactivated brewer's yeast have been used as well in ruminants diets, conse‐ quently it was observed an increase in productivity of animal meat or milk [73, 82], but also live yeast cultures have been used. These are prepared by inoculating wet cereal grains or grain by-products with live yeast, partially fermenting the mash, and then drying the entire medium without killing yeast or destroying vitamins and enzymes [73]. Live yeast is report‐ ed to stimulate fermentation in the rumen through its ability to stimulate the development of anaerobic, cellulolytic and acid lactic bacteria fermentations. In addition, the ingestion of yeast offers continuous supply of vitamins, dicarboxylic acids, removal of oxygen, buffering effect, and reduction in the number of protozoa. As a result, there is an improvement of the digestion of the fibrous and cellulolytic portion of the diet, which leads to a greater intake of food and better performance [83, 84].

Dried yeast was used traditionally in poultry diets in the past as a source of aminoacids and micronutrients, and though the broiler growth was improving this practice was largely dis‐ continued for economic reasons [77]. On the other hand, brewer's yeast appears to be espe‐ cially beneficial for breeder turkeys and laying hens [85]. Reproductive improvements are attributed to the high level of dietary biotin and selenium in yeast, which is more beneficial than inorganic selenium added to poultry diets [86] and it contributes for the prevention of biotin deficiency in poultry diets, which may result in reduced feed conversion, low egg production, and poor hatchability [87]. Brewer's yeast is also very rich in folic acid, an im‐ portant vitamin for turkeys [73].

Brewer's yeast has been recognized to have potential as well as a substitute for live food in the production of certain fish or as a potential replacement for fishmeal [88-90]. In addition, it has low content in phosphorous, meaning less water and environmental contamination than common fish meal and other plant-based alternate protein sources [91]. Multiple stud‐ ies have demonstrated the immunostimulant properties of yeasts, such as their ability to en‐ hance non-specific immune activity [92]. That reaction can be related to β-glucans, nucleic acids as well as mannan oligosaccharides [93]. Brewer's yeast may serve as an excellent health promoter for fish culture as even when administered for relatively long periods is able to enhance immune responses as well as growth of various fish species, without caus‐ ing immunosuppression [94, 95]. Furthermore, the relative high levels of nucleic acid nitro‐ gen present (mostly in the form of RNA) that in humans and most monogastric animals can became toxic if taken in excess, as the capacity of excretion of the uric acid formed is limited [96], in fish does not happen due to their very active liver uricase [97].

#### **4.2. Human little treats, big benefits**

for animals [72]. Yeasts have been fed to animals for more than a hundred years, either in the form of yeast fermented mash produced on the farm, yeast by-products from breweries or distilleries, or commercial yeast products specifically produced for animal feeding. In ani‐ mals, including pets, this practice is used to compensate for the amino acid and vitamin de‐

Brewer's yeast biomass, as described above, which results from the cultivation of *S. cerevisiae* on malted barley, separated after the *wort* fermentation, debittered and then dried, is the second major by-product from brewing industry, just after the brewer spent grain [73]. This biomass is an excellent source of proteins, peptides and amino acids, vitamins (especially of B-group: B1, B2, PP, B5, B6, B8, B12), minerals and trace elements (calcium, phosphorus, po‐ tassium, magnesium, copper, iron, zinc, manganese, chromium, selenium), carbohydrates (glucans and mannans), as well as phospholipids [75]. The winemaking industry also gener‐ ates a huge amount of microbial biomass - **leeds**. Yet, this incorporates the yeasts (that die due to nutrient depletion) but also other microorganisms, suspended solids, colloids, and organic matter, and have been shown to display quite low nutritional value to be considered

Those yeast used for monogastrics food or feeding rations is generally inactivated because feeding of live yeast might cause avitaminosis due to the depletion of B-vitamins in the in‐ testine [77]. They can also cause adverse fermentation in the digestive tract of swine leading to diarrhoea and bloating [75]. Yeasts can be killed through application of heat or using chemicals. High temperature destroys the yeast membrane, but does not necessarily inacti‐ vate all yeast enzymes, unless quite elevated temperatures are applied. Alternatively, there are the chemical treatments with propionic acid or formic acid, which also act as a preserva‐

Yeasts have been used in diets of numerous species with varying levels of success. Yeast for swines is sold for feed applications as wet slurry, as dried brewer's yeast, or in mixtures with other brewery by-products [73]. It is ideal for their feed as a good protein source, it contains most of the essential amino acids in adequate quantities, and numerous vitamins, selenium, copper, and phosphorus. Selenium concentrations are much higher in yeast than in soybean meal, and deficiency of this compound in the swine's alimentation has been the cause of high‐ er swine mortality [78, 79]. Additionally, dried brewer's yeast contains mannan oligosacchar‐ ides, which have been reported to increase the growth performance and intestinal health of

Either live or inactivated brewer's yeast have been used as well in ruminants diets, conse‐ quently it was observed an increase in productivity of animal meat or milk [73, 82], but also live yeast cultures have been used. These are prepared by inoculating wet cereal grains or grain by-products with live yeast, partially fermenting the mash, and then drying the entire medium without killing yeast or destroying vitamins and enzymes [73]. Live yeast is report‐ ed to stimulate fermentation in the rumen through its ability to stimulate the development of anaerobic, cellulolytic and acid lactic bacteria fermentations. In addition, the ingestion of yeast offers continuous supply of vitamins, dicarboxylic acids, removal of oxygen, buffering effect, and reduction in the number of protozoa. As a result, there is an improvement of the

pigs [80]. Benefits have been described as well for nursing and weanling pigs [81].

ficiencies of cereals [73, 74], and in fish as a substitute for other ingredients [71].

for use as a supplement in animal feed [76].

536 Food Industry

tives for yeast, and contribute to the feed value of the yeast [73].

In a world of rapidly increasing population and low agricultural production, yeasts are rela‐ tively cheap and easily produced on an industrial scale representing a sustainable alternate protein source to cover the population nutritional demands. The first time that yeast was cultivated in large scale for human nutritional use was in Germany during both World Wars [72]. The yeasts *S. cerevisiae* as baker yeast, *Candida utilis* as torula yeast, and *Kluyveromyces fragilis* as whey yeast, when produced on suitable, food grade substrates (*e.g.*, sugars, etha‐ nol, and lactose), are permitted in many foods around the world [70]. Besides the alcoholic beverages and baking products referred above, yeast are used in the health food industry; as additives, conditioners, and flavouring agents; as sources of high nutritional value proteins, enzymes, nucleic acids, nucleotides, and cell wall polysaccharides [98] as well as for the pro‐ duction of food-grade yeast extracts and autolysates [69, 99]. Yeast extract from dried brew‐ er's yeast cells can be used by enzymatic treatment in a wide variety of foods (*e.g.*, meat products, sauces and gravies, soups, chips and crackers) as flavours enhancers or potentia‐ tors [73, 100]. β-Glucan obtained from brewer's yeast can be used in food products as a thickening, water-holding, or oil-binding agent and emulsifying stabilizer [101]. The probi‐ otic activity is an additional role of some yeast that is attracting increasing interest [102].

*S. cerevisiae* has been studied extensively for its medicinal properties and several beneficial/ probiotic effects on human health and well-being have been reported, including prevention and treatment of intestinal diseases and immunomodulatory actions, are the most wellknown. Probiotics are viable microorganisms that are beneficial to the host when consumed in appropriate quantities [103]. The probiotic properties of yeasts reported refer the ability to sur‐ vive through the gastrointestinal tract and interact antagonistically with gastrointestinal pathogens. As described above, *S. cerevisiae* have been used as supplements to animal and fish feeds with reported improvements on the growth and health of the hosts [104]. Regarding hu‐ mans, *S. cerevisiae* var. *boulardii* has been successfully used as an oral biotherapeutic agent to treat patients with severe cases of diarrhoea (*e.g.,* antibiotic-associated diarrhoea and travel‐ ler's diarrhoea) and other gastrointestinal disorders (*e.g.*, irritable bowel syndrome and Crohn's disease) [105]. Several studies have shown that *S. cerevisiae* var. *boulardii* confer benefi‐ cial effects against various enteric pathogens, involving different mechanisms as: i) preven‐ tion of bacterial adherence and translocation in the intestinal epithelial cells, ii) production of factors that neutralize bacterial toxins and iii) modulation of the host cell signalling pathway associated with pro-inflammatory response during bacterial infection [106]. As reviewed in detail in [106] prevention of bacterial adherence and translocation in the intestinal epithelial cells is due to the fact that the cell wall of *S. cerevisiae* var. *boulardii* has the ability to bind enter‐ opathogens, which results in a decrease of their adherence to host epithelial cells. This yeast al‐ so produces proteins that are responsible for degradation, neutralisation or dephosphorylation of bacterial toxins. Moreover, the mechanism by which *S. cerevisiae* var. *boulardii* modifies host cell signalling pathways associated with pro-inflammatory response is based on blocking activation of nuclear factor-kappa B (NF-κB) and mitogen activated pro‐ tein kinase (MAPK) which decreases the expression of inflammation-associated cytokines such as interleukin 8 (IL-8), tumor necrosis factor alpha (TNF-α) and interferon gamma (IFNγ). Conversely, *S. cerevisiae* var. *boulardii* also stimulates the peroxisome proliferator-activated receptor gamma (PPAR-γ) expression in human colonocytes and reduces the response of hu‐ man colon cells to pro-inflammatory cytokines. There are several studies indicating the stimu‐ lation of the host cell immunity, both innate and adaptive immunity, by yeast in response to pathogen infections. Furthermore, it has been shown that *S. cerevisiae* var. *boulardii* also has a role in the maintenance of epithelial barrier integrity; during bacterial infection the tight junc‐ tions are disrupted and this yeast enhances the ability of intestinal epithelial cells to restore the tight-junction structure and the barrier permeability [106].

**4.3. What the future holds**

**Acknowledgements**

**Author details**

**References**

Elsevier; 2011.

Since *S. cerevisiae* var. *boulardii* is recognised as a member of the species *S. cerevisiae*, it is most likely that also other strains within *S. cerevisiae* might show probiotics properties. So far, great efforts have been placed on utilising the probiotic effects of especially LAB, where‐ as rather limited emphasis has been placed on the beneficial effects offered by yeast. How‐ ever, yeasts offer several advantages compared to LAB. They have a more diverse enzymatic profile and appear to have a more versatile effect on the immune system. They also provide protection against pathogenic bacteria and toxic compounds by surface binding and appear to be better suited for nutritional enrichment and delivery of bio-active molecules. Besides, yeast is much more robust than LAB and therefore easier to produce and to distribute, espe‐ cially in less developed areas [106]. Furthermore and though there is still much room for im‐ provement, also the encapsulation technology applied to probiotics has shown benefits, *e.g.*, *S. cerevisiae* var. *boulardii* in microspheres protect the yeast from destruction in the gastroin‐

Yeast: World's Finest *Chef* http://dx.doi.org/10.5772/53156 539

testinal tract and therefore increase intestinal delivery of the viable probiotic [114].

FCT (Fundação para a Ciência e a Tecnologia) project PEst-C/BIA/UI4050/2011.

University of Minho/ CBMA (Centre of Molecular and Environmental Biology), Portugal

[1] Kurtzman CP, Fell JW, Boekhout T. The Yeasts: A Taxonomic Study. Amsterdam:

[2] Tulha J, Carvalho J, Armada R, Faria-Oliveira F, Lucas C, Pais C, Almeida J, Ferreira C. Yeast, the Man's Best Friend. In: Valdez B. (ed.) Scientific, Health and Social As‐

pects of the Food Industry. Rijeka: InTech; 2012. p255-278.

Fábio Faria-Oliveira, Sónia Puga and Célia Ferreira

Authors would like to acknowledge Hugh S. Johnson for the several critical readings of the manuscript regarding proper English usage and Maria Manuel Azevedo for reviewing the manuscript and for valuable suggestions. Fábio Faria-Oliveira is supported by a PhD grant from FCT-SFRH/BD/45368/2008. This work was financed by FEDER through COMPETE Programme (Programa Operacional Factores de Competitividade) and national funds from

The benefits from ingesting yeasts do not stop here, many other have been reported as: se‐ lectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon [107], *e.g.,* fructooligosaccharides [108]; decreasing the serum cholesterol levels [109], in the treatment of diabetes (regulation of insulin levels) and chronic acne, reducing the ap‐ petite, for healthy hair and nails [70, 110, 111] and also for promoting the bioavailability of minerals through the hydrolysis of phytate, folate biofortification and detoxification of my‐ cotoxins due to surface binding to the yeast cell wall [106]. Yet, still are some concerns about public health safety as cause of crescent reports associating the intake of yeast with cases of fungaemia [112, 113].

### **4.3. What the future holds**

*S. cerevisiae* has been studied extensively for its medicinal properties and several beneficial/ probiotic effects on human health and well-being have been reported, including prevention and treatment of intestinal diseases and immunomodulatory actions, are the most wellknown. Probiotics are viable microorganisms that are beneficial to the host when consumed in appropriate quantities [103]. The probiotic properties of yeasts reported refer the ability to sur‐ vive through the gastrointestinal tract and interact antagonistically with gastrointestinal pathogens. As described above, *S. cerevisiae* have been used as supplements to animal and fish feeds with reported improvements on the growth and health of the hosts [104]. Regarding hu‐ mans, *S. cerevisiae* var. *boulardii* has been successfully used as an oral biotherapeutic agent to treat patients with severe cases of diarrhoea (*e.g.,* antibiotic-associated diarrhoea and travel‐ ler's diarrhoea) and other gastrointestinal disorders (*e.g.*, irritable bowel syndrome and Crohn's disease) [105]. Several studies have shown that *S. cerevisiae* var. *boulardii* confer benefi‐ cial effects against various enteric pathogens, involving different mechanisms as: i) preven‐ tion of bacterial adherence and translocation in the intestinal epithelial cells, ii) production of factors that neutralize bacterial toxins and iii) modulation of the host cell signalling pathway associated with pro-inflammatory response during bacterial infection [106]. As reviewed in detail in [106] prevention of bacterial adherence and translocation in the intestinal epithelial cells is due to the fact that the cell wall of *S. cerevisiae* var. *boulardii* has the ability to bind enter‐ opathogens, which results in a decrease of their adherence to host epithelial cells. This yeast al‐ so produces proteins that are responsible for degradation, neutralisation or dephosphorylation of bacterial toxins. Moreover, the mechanism by which *S. cerevisiae* var. *boulardii* modifies host cell signalling pathways associated with pro-inflammatory response is based on blocking activation of nuclear factor-kappa B (NF-κB) and mitogen activated pro‐ tein kinase (MAPK) which decreases the expression of inflammation-associated cytokines such as interleukin 8 (IL-8), tumor necrosis factor alpha (TNF-α) and interferon gamma (IFNγ). Conversely, *S. cerevisiae* var. *boulardii* also stimulates the peroxisome proliferator-activated receptor gamma (PPAR-γ) expression in human colonocytes and reduces the response of hu‐ man colon cells to pro-inflammatory cytokines. There are several studies indicating the stimu‐ lation of the host cell immunity, both innate and adaptive immunity, by yeast in response to pathogen infections. Furthermore, it has been shown that *S. cerevisiae* var. *boulardii* also has a role in the maintenance of epithelial barrier integrity; during bacterial infection the tight junc‐ tions are disrupted and this yeast enhances the ability of intestinal epithelial cells to restore the

tight-junction structure and the barrier permeability [106].

fungaemia [112, 113].

538 Food Industry

The benefits from ingesting yeasts do not stop here, many other have been reported as: se‐ lectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon [107], *e.g.,* fructooligosaccharides [108]; decreasing the serum cholesterol levels [109], in the treatment of diabetes (regulation of insulin levels) and chronic acne, reducing the ap‐ petite, for healthy hair and nails [70, 110, 111] and also for promoting the bioavailability of minerals through the hydrolysis of phytate, folate biofortification and detoxification of my‐ cotoxins due to surface binding to the yeast cell wall [106]. Yet, still are some concerns about public health safety as cause of crescent reports associating the intake of yeast with cases of

Since *S. cerevisiae* var. *boulardii* is recognised as a member of the species *S. cerevisiae*, it is most likely that also other strains within *S. cerevisiae* might show probiotics properties. So far, great efforts have been placed on utilising the probiotic effects of especially LAB, where‐ as rather limited emphasis has been placed on the beneficial effects offered by yeast. How‐ ever, yeasts offer several advantages compared to LAB. They have a more diverse enzymatic profile and appear to have a more versatile effect on the immune system. They also provide protection against pathogenic bacteria and toxic compounds by surface binding and appear to be better suited for nutritional enrichment and delivery of bio-active molecules. Besides, yeast is much more robust than LAB and therefore easier to produce and to distribute, espe‐ cially in less developed areas [106]. Furthermore and though there is still much room for im‐ provement, also the encapsulation technology applied to probiotics has shown benefits, *e.g.*, *S. cerevisiae* var. *boulardii* in microspheres protect the yeast from destruction in the gastroin‐ testinal tract and therefore increase intestinal delivery of the viable probiotic [114].

## **Acknowledgements**

Authors would like to acknowledge Hugh S. Johnson for the several critical readings of the manuscript regarding proper English usage and Maria Manuel Azevedo for reviewing the manuscript and for valuable suggestions. Fábio Faria-Oliveira is supported by a PhD grant from FCT-SFRH/BD/45368/2008. This work was financed by FEDER through COMPETE Programme (Programa Operacional Factores de Competitividade) and national funds from FCT (Fundação para a Ciência e a Tecnologia) project PEst-C/BIA/UI4050/2011.

## **Author details**

Fábio Faria-Oliveira, Sónia Puga and Célia Ferreira

University of Minho/ CBMA (Centre of Molecular and Environmental Biology), Portugal

## **References**

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**Chapter 24**

ton/year; of this amount only 50% is

**Valorisation of Cheese Whey, a By-Product from the**

Whey is the by-product of cheese or casein production, it is of relative importance in the dai‐ ry industry due to the large volumes produced and the nutritional composition. Worldwide

processed [1]. Approximately 50% of worldwide cheese-whey (CW) production is treated and transformed into various food and feed products. About half of this amount is used di‐ rectly in liquid form, 30% as powdered cheese-whey, 15% as lactose and its byproducts and

plus of whey is 13×106 tons, containing about 619,250 tons of lactose. Nowadays this surplus is not utilized for further production of lactose; consequently, whey disposal represents a se‐ rious problem from both an economical and an environmental point of view. On the contra‐ ry, recovery of whey components and/or use of whey as fermentation medium may be

Whey contains more than half of the solids present in the original whole milk, including whey proteins (20% of the total protein) and most of the lactose, water-soluble vitamins and minerals. Consequently, whey can be considered a valuable by-product with several appli‐

From a valorization point of view, two different options in CW management can be consid‐ ered: the first one is based on the application of technologies to recover valuable compounds such as proteins and lactose. Currently, valorization processes applied to CW constitute the preferential option to treat this by-product, only exceeded by the production of powdered CW. The second option relies on the application of fermentation processes to obtain value

advantageous not only for the environment but also for a sustainable economy [4,5].

tons/year of whey is produced in the European Union [3]; the annual sur‐

© 2013 Mollea et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

© 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution,

distribution, and reproduction in any medium, provided the original work is properly cited.

and reproduction in any medium, provided the original work is properly cited.

Chiara Mollea, Luca Marmo and Francesca Bosco

Additional information is available at the end of the chapter

whey production is estimated at around 180 to 190×106

the rest as cheese whey- protein concentrates [2].

cations in the food and pharmaceutical industries.

**Dairy Industry**

http://dx.doi.org/10.5772/53159

**1. Introduction**

A total of 40×106