*Article* **Application Research: Big Data in Food Industry**

**Qi Tao 1, Hongwei Ding 1, Huixia Wang 2 and Xiaohui Cui 1,\***

**Abstract:** A huge amount of data is being produced in the food industry, but the application of big data—regulatory, food enterprise, and food-related media data—is still in its infancy. Each data source has the potential to develop the food industry, and big data has broad application prospects in areas like social co-governance, exploit of consumption markets, quantitative production, new dishes, take-out services, precise nutrition and health management. However, there are urgent problems in technology, health and sustainable development that need to be solved to enable the application of big data to the food industry.

**Keywords:** food industry; big data; application prospect; sustainable development


**10. Conclusion**

The mechanisms of neuroimmunopathogenesis, the most significant and complicated aspect of TE, were covered in this chapter, which was the product of much study and effort. Each part has been thoroughly evaluated and clarified. Therefore, the most fundamental aspect of avoiding neuropathology induced by TE, which may lead to mortality, is the investigation and complete disclosure of these processes. This book chapter, which discusses this extensive neuroimmunopathogenesis and will play an essential role in developing novel therapeutic medications, will make a significant addition to the body of literature. Furthermore, diagnostic methods that are critical are emphasized. The tricks of imaging methods are summarized, and key points are highlighted. It is hoped that considering all aspects of TE, which has a complex pathological mechanism, will make a significant contribution to the literature.


**4. Physical exercise**

Physical activity is currently recognized as a potent tool for the prevention of chronic degen‐ erative diseases, including CVDs and common tumors, such as those affecting the colon, breast, prostate and endometrium [28].

association cannot be established. The inconsistency of the results reflects the limitations of human studies, the diet differences, the pre-existing total anti-oxidant status, the stage of disease, the interaction between dietary modulation and genetic composition of indi‐ viduals, the dosage and duration of supplementation, the age and the sex. On the other hand, studies in animal models of atherosclerosis clearly show an atheroprotective effect of dietary anti-oxidants, however, they focus mainly on early atherosclerotic events and

Atherosclerosis and Current Anti-Oxidant Strategies for Atheroprotection

http://dx.doi.org/10.5772/53035

7

Cardiovascular prevention and treatment strategies should consider the simple, direct and inexpensive dietary approach as a first-line strategy to the burgeoning burden of CVDs,

In this review we focus our attention on the main natural anti-oxidants contained in food

Polyphenols are the most abundant anti-oxidants in human diet and are common constitu‐ ents of foods of plant origin and are widespread constituents of fruits, vegetables, cereals,

They are defined according to the nature of their backbone structures: phenolic acids, flavo‐ noids and the less common stilbenes and lignans. Among these, flavonoids are the most abundant polyphenols in the diet [34]. Despite their wide distribution, the health effects of dietary polyphenols have been attentively studied only in recent years [32] and several stud‐ ies, although not all, have found an inverse association between polyphenol consumption

Polyphenols exert anti-atherosclerotic effects in the early stages of atherosclerosis devel‐ opment, they decrease LDL oxidation, improve endothelial function, increase vasorelaxa‐ tion, modulate inflammation and lipid metabolism, improve anti-oxidant status and protect against atherothrombotic events including myocardial ischemia and platelet ag‐

Many polyphenols have direct anti-oxidant properties, acting as reducing agents, and may react with reactive chemical species forming products with much lower reactivity. Polyphenols may also affect indirectly the redox status by increasing the capacity of en‐ dogenous anti-oxidants or by inhibiting enzymatic systems involved in ROS formation [36]. The free-radical scavenging activity of many polyphenols has been reported to be much stronger than that of vitamin C, vitamin E or glutathione, the major anti-oxidants

In spite of their potent protective effects in the development of atherosclerosis, little is

olive, legumes, chocolate and beverages, such as tea, coffee and wine [32,33].

not in advanced atherosclerosis as in humans [27].

and on their primary diet source.

**6. Polyphenol**

and CVDs motality [35].

gregation [35].

present in the body.

known about aortic distribution of polyphenols [34].

alone or in combination with pharmalogic treatments [10].

There is a body of clinical and experimental evidence showing that voluntary and imposed physical exercise prevents the progression of CVDs and reduces cardiovascular morbidity and mortality. Therefore a physically active state is an appropriate and natural biological condition for human and most animal species [3].

It has been demonstrated that exercise slows the progression of atherosclerosis, promoting its stabilization and preventing plaque rupture in a variety of hypercholesterolaemic animal models, such as apolipoproteinE-deficient mice and LDL receptor-deficient mice, whereas physical inactivity accelerates it [3,29].

Exercise increases blood anti-oxidant capacity through elevating hydrophilic anti-oxi‐ dants (uric acid, bilirubin and vitamin C) and decreases lipophilic anti-oxidants (carote‐ noids and vitamin E) [28]. It is noteworthy that exercise prevents plaque vulnerability and atherosclerosis progression without necessarily correcting classic risk factors, such as hypercholesterolaemia, endothelial dysfunction and high blood pressure, suggesting that exercise can directly affect plaque composition and phenotype, thus preventing the ap‐ pearance of fatal lesions. Besides the effect of diet and drugs, the protective role of regu‐ lar exercise against atherosclerosis is well established and its beneficial atheroprotective effects are not limited to one particular cell, but to a variety of cells and tissues involved in the pathogenesis of atherosclerosis and metabolic disorders, such as macrophages and adipose tissue [3].

Regular exercise and a correct diet would be natural atheroprotective approaches which has been forgotten by modern societies.


**2.1 Cruciferous vegetables**

Cruciferous vegetables belong to *Brassica* genus, Brassicaceae family which are usually known as broccoli, Brussels sprouts, cabbage, cauliflower, kale, and radishes and commonly used for food consumption. They are not only rich sources of fibers, vitamins, and carotenoids as their important components, but also contain higher glucosinolate content than other vegetables [10]. Glucosinolates are secondary metabolites in cruciferous veggies and can be divided into three classes based on their structure: aliphatic glucosinolates, indole glucosinolates, and aromatic glucosinolates.

Nearly 200 types of glucosinolates have been reported in scientific literature, especially glucobrassicin and glucoraphanin. These two compounds can be transformed into hydrolysis products such as isothiocyanates, sulforaphane (SF), and indole-3-carbinol (I3C) by β-thioglucosidase (myrosinase) enzyme when plant cells are damaged. This mechanism could also be processed by bacteria in the gastrointestinal tract [11, 12].

**265**

*Modulation of Edible Plants on Hepatocellular Carcinoma Induced by Aflatoxin B1*

angiogenesis, and also induce an apoptosis of cancer cells [11].

hepatocytes were observed after induction of SF [18].

The current epidemiological and clinical studies revealed that only lung, colorectal, breast, prostate, and pancreatic cancers were given the positive response to glucosinolates while animal model showed the effective inhibition of liver cancer and other cancer types through various mechanisms. Nevertheless, randomized clinical trial of glucosinolates on liver cancer showed different results [11, 19]; comparison between broccoli sprout extract treatments and control group was studied simultaneously. After treatment, AFB1-DNA adducts were clearly determined. The results indicated that no significant difference was observed among tested groups on AFB1-DNA adduct level (p = 0.68). On the contrary, an inverse linear correlation of dithiocarbamates, a metabolite of sulforaphane, and AFB1-DNA adduct excretion was noted (p = 0.002, R = 0.31). It can be implied that exposure to glucosinolates might decrease AFB1-induced toxicity [20]. Besides, various compounds of

The studies of anticancer effects of glucosinolates and their hydrolysis products revealed that numerous existing compounds also had anticancer mechanism against various types of cancers. For instance, the presence of sulforaphane could suppress carcinogen and prevent DNA adduct (a biomarker of AFB1 exposure) directly through an inhibition of phase I metabolism enzymes. At the same time, it induces phase II metabolism enzymes which play an important role in converting carcinogens to the inactive metabolites and excreting from the body. Their hydrolysis products exhibit an ability to scavenge the free radicals, inhibit inflammation and

Previous studies investigated the effects of bioactive compounds such as I3C and 1-cyano-2 hydroxy-3 butene (Crambene), derivatives of glucosinolate group found in cruciferous veggies, on HCC occurrence. Glucosinolates did not only respond for abnormal liver cells, but they also enhance AFB1 detoxification in the rat model. Pre-exposure to the high-dose combination of I3C and Crambene (0.15 and 0.165%, respectively) protected the liver cells effectively more than low-dose combinations and single exposure [13]. Risk reduction of liver cancer could also be observed in rainbow trout when pre-exposed to I3C at the dose 2000 ppm prior to AFB1; however, the adverse effects and increase of liver cancer incidence were reported when the exposure sequence was reversed [14]. In addition, further studies revealed a dosedependent relationship between I3C dose after exposure to AFB1 and the incidence of liver cancer and other cancer types [15]. Thus, it could be summarized that the incidence of liver cancer is induced by AFB1 relating to timing of I3C exposure. Preexposure to I3C prior to AFB1 reduced the liver cancer incidence, but post-exposure reversely raised the liver cancer incidence [15]. Accordingly, subsequent mechanistic studies indicated an induction of I3C on phase I and II metabolism enzyme activities [16]. Continuous exposure to I3C might enhance phase II enzyme activity, so the absorbed AFB1 would be excreted rapidly. In contrast, pre-exposure to AFB1 triggered the adverse effects such as DNA abnormality and increase of liver cancer risk. The explanation was that pre-exposure to AFB1 generates AFB1-8,9-epoxide and this reactive metabolite would be more activated when treated later with I3C. In addition, I3C could be able to induce both phase I and II metabolism enzyme activities, thus AFB1-8,9-epoxide was more generated as a result of activation of phase I metabolism. Although phase II enzyme was also stimulated, it was not enough to eliminate AFB1. Not only I3C is frequently reported, but other glucosinolate derivatives like SF and H-1,2-dithiole-3-thione (D3T) are also stated. For example, while rats were preexposed to these derivatives, AFB1-DNA adduct in rat's liver was reduced due to an increase of GST activity, a phase II detoxification enzyme for AFB1 [17]. Likewise, other previous studies reported that SF could competitively inhibit CYP1A2 in human liver cells [16], causing a decrease of AFB1-DNA adduct. Remarkably, upregulation of gene expression-related tissue repairing system and number of

*DOI: http://dx.doi.org/10.5772/intechopen.87296*

#### *Modulation of Edible Plants on Hepatocellular Carcinoma Induced by Aflatoxin B1 DOI: http://dx.doi.org/10.5772/intechopen.87296*

The studies of anticancer effects of glucosinolates and their hydrolysis products revealed that numerous existing compounds also had anticancer mechanism against various types of cancers. For instance, the presence of sulforaphane could suppress carcinogen and prevent DNA adduct (a biomarker of AFB1 exposure) directly through an inhibition of phase I metabolism enzymes. At the same time, it induces phase II metabolism enzymes which play an important role in converting carcinogens to the inactive metabolites and excreting from the body. Their hydrolysis products exhibit an ability to scavenge the free radicals, inhibit inflammation and angiogenesis, and also induce an apoptosis of cancer cells [11].

Previous studies investigated the effects of bioactive compounds such as I3C and 1-cyano-2 hydroxy-3 butene (Crambene), derivatives of glucosinolate group found in cruciferous veggies, on HCC occurrence. Glucosinolates did not only respond for abnormal liver cells, but they also enhance AFB1 detoxification in the rat model. Pre-exposure to the high-dose combination of I3C and Crambene (0.15 and 0.165%, respectively) protected the liver cells effectively more than low-dose combinations and single exposure [13]. Risk reduction of liver cancer could also be observed in rainbow trout when pre-exposed to I3C at the dose 2000 ppm prior to AFB1; however, the adverse effects and increase of liver cancer incidence were reported when the exposure sequence was reversed [14]. In addition, further studies revealed a dosedependent relationship between I3C dose after exposure to AFB1 and the incidence of liver cancer and other cancer types [15]. Thus, it could be summarized that the incidence of liver cancer is induced by AFB1 relating to timing of I3C exposure. Preexposure to I3C prior to AFB1 reduced the liver cancer incidence, but post-exposure reversely raised the liver cancer incidence [15]. Accordingly, subsequent mechanistic studies indicated an induction of I3C on phase I and II metabolism enzyme activities [16]. Continuous exposure to I3C might enhance phase II enzyme activity, so the absorbed AFB1 would be excreted rapidly. In contrast, pre-exposure to AFB1 triggered the adverse effects such as DNA abnormality and increase of liver cancer risk. The explanation was that pre-exposure to AFB1 generates AFB1-8,9-epoxide and this reactive metabolite would be more activated when treated later with I3C. In addition, I3C could be able to induce both phase I and II metabolism enzyme activities, thus AFB1-8,9-epoxide was more generated as a result of activation of phase I metabolism. Although phase II enzyme was also stimulated, it was not enough to eliminate AFB1.

Not only I3C is frequently reported, but other glucosinolate derivatives like SF and H-1,2-dithiole-3-thione (D3T) are also stated. For example, while rats were preexposed to these derivatives, AFB1-DNA adduct in rat's liver was reduced due to an increase of GST activity, a phase II detoxification enzyme for AFB1 [17]. Likewise, other previous studies reported that SF could competitively inhibit CYP1A2 in human liver cells [16], causing a decrease of AFB1-DNA adduct. Remarkably, upregulation of gene expression-related tissue repairing system and number of hepatocytes were observed after induction of SF [18].

The current epidemiological and clinical studies revealed that only lung, colorectal, breast, prostate, and pancreatic cancers were given the positive response to glucosinolates while animal model showed the effective inhibition of liver cancer and other cancer types through various mechanisms. Nevertheless, randomized clinical trial of glucosinolates on liver cancer showed different results [11, 19]; comparison between broccoli sprout extract treatments and control group was studied simultaneously. After treatment, AFB1-DNA adducts were clearly determined. The results indicated that no significant difference was observed among tested groups on AFB1-DNA adduct level (p = 0.68). On the contrary, an inverse linear correlation of dithiocarbamates, a metabolite of sulforaphane, and AFB1-DNA adduct excretion was noted (p = 0.002, R = 0.31). It can be implied that exposure to glucosinolates might decrease AFB1-induced toxicity [20]. Besides, various compounds of

*Phytochemicals in Human Health*

products such as rice, chili, and peanuts. AFB1 is a Class 1 carcinogen classified by the International Agency for Research on Cancer (IARC), suggesting sufficient evidence of carcinogenicity caused by AFB1 in both animals and human [4]. Consequently, it is considered as a serious contaminant in many foodstuffs.

Once the AFB1 is absorbed through human body, it is metabolized at the liver site by phase I metabolizing enzymes including hydroxylation, hydration, demethylation, and epoxidation. Nontoxic metabolites are resulted from hydroxylation, hydration, and demethylation while the reactive metabolite, AFB1-8,9-epoxide, is resulted from epoxidation [3, 4]. AFB1-8,9-epoxide is the genotoxic form and can react efficiently with DNA at the N7 site of guanine to form AFB1 adduct. This adduct can adversely affect DNA sequence and genetic materials. However, human defensive mechanisms are able to detoxify AFB1 toxicity through phase II metabolism enzymes. AFB1 can be converted into excretable forms after binding with glutathione and glucuronic acid generated by specific enzyme, glutathione S-transferase (GST) and UDP-glucuronosyltransferase (UGT), respectively [5–7]. Besides acute toxicity such as hepatic necrosis, bile drug proliferation, edema, and

lethargy could also be observed after exposure to high dose of AFB1 [8].

toxicity by polyphenol-containing plants.

**2.1 Cruciferous vegetables**

**2. Effects of edible plants on toxicity induced by AFB1**

Regarding the current situation, there are many ways to avoid the risk of AFB1 induced liver cancer as determined by two main periods, pre- and post-harvest period and exposure period [6]. During harvest time, several techniques are used for controlling and reducing the chance of harmful effects resulted from AFB1: cultivation of AFB1 tolerance plants, biocontrol using competitive fungi, irrigation, and insecticide. For exposure period, most researches aim to determine the effects of several foods or supplementary foods that are capable of decreasing AFB1 induced toxicity. For example, oltipraz, a synthetic derivative of natural compound originated from cruciferous vegetables, is reported on its capacity to reduce AFB1 toxicity. In addition, green tea polyphenol and chlorophyllin (a derivative of chlorophyll found in green leafy vegetables) are also stated. These natural compounds have a potential against AFB1-induced hepatocarcinogenicity by decreasing the absorption of AFB1, controlling metabolic pathway, and increasing AFB1 excretion [6, 9]. To update the involvement of edible plants as chemoprevention for AFB1, this review is aimed to emphasize the mechanistic alleviation of AFB1-induced liver

Cruciferous vegetables belong to *Brassica* genus, Brassicaceae family which are usually known as broccoli, Brussels sprouts, cabbage, cauliflower, kale, and radishes and commonly used for food consumption. They are not only rich sources of fibers, vitamins, and carotenoids as their important components, but also contain higher glucosinolate content than other vegetables [10]. Glucosinolates are secondary metabolites in cruciferous veggies and can be divided into three classes based on their structure: aliphatic glucosinolates, indole glucosinolates, and aromatic

Nearly 200 types of glucosinolates have been reported in scientific literature, especially glucobrassicin and glucoraphanin. These two compounds can be transformed into hydrolysis products such as isothiocyanates, sulforaphane (SF), and indole-3-carbinol (I3C) by β-thioglucosidase (myrosinase) enzyme when plant cells are damaged. This mechanism could also be processed by bacteria in the gastroin-

**264**

glucosinolates.

testinal tract [11, 12].

glucosinolates have the potential to increase excretion of many carcinogens through glutathione *S*-transferase stimulation. Once the GST was stimulated, carcinogenicity and risk of diseases in human were also decreased [21].

## **2.2 Green tea**

Green tea, *Camellia sinensis,* is a beverage that contains high contents of phenolic compounds at approximately 30% of dry weight. One of the major phenolic compounds in green tea is catechin, particularly epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG), and epicatechin (EC) [22].

Recent studies have demonstrated the positive effects of green tea on many diseases and adverse human health conditions such as coronary artery disease, oral heath, bone integrity, thermoregulation balance, and kidney stones. Furthermore, an association between green tea consumption and the incidence of many types of cancer has also been reported such as oral and pharynx, esophageal, gastric, colorectal, bladder, prostate, breast, lung, skin, leukemia, pancreatic, and liver cancers [23, 24]. Various research methods including preclinical studies (*in vitro* and *in vivo*), epidemiology, and clinical trial were used to investigate the effect of crude green tea extract or single compound like EGCG on many types of cancer [25]. Overall, an anti-cancer mechanism of green tea extracts against cancer cells was evidently elucidated. Green tea extracts were able to induce apoptosis of cancer cells through inhibiting nuclear factor kappa light chain enhancer of activated B cells (NF-κB) activity and B-cell lymphoma extra-large (Bcl-xL) mRNA expression. Besides, the reduction of angiogenesis of cancer cells was also resulted by green tea extracts through inhibition of vascular endothelial growth factor (VEGF) expression [26].

Previous studies have been reported on several protective ways against AFB1 induced liver cancer from the exposure to catechin compounds and green tea extracts. For example, the reduction of chromosome aberration in rat bone marrow cells was observed after pre-exposure with green tea or EGCG for 24 hours prior to AFB1 [27]. Besides, hepatic nuclear AFB1-DNA binding and glutathione S-transferase placental form (GST-P) positive single hepatocyte, specific markers of hepatocarcinogenic potential in the rat model, were also reduced after pre-exposure with green tea extracts for 2–4 weeks prior to AFB1 [28]. Similarly, the levels of GST-P and γ-glutamyl transpeptidase positive hepatic foci induced by AFB1 and carbon tetrachloride were reduced during pre- or co-treatment with green tea extracts. Furthermore, the inhibition of hepatocarcinogenesis was also observed [29].

The studies of green tea against AFB1-induced human liver cancer are still currently limited, and most reports have been retrieved from China. As some Chinese commonly consume food contaminated with AFB1, the risk of HCC is higher than other regions. A clinical study demonstrated a protective effect of 500 and 1000 mg/day green tea polyphenol (GTP) on hepatocarcinogenesis in 124 HCC patients who presented with HBsAg and aflatoxin-albumin adducts. Results showed that 8-hydroxydeoxyguanosine (8-OHdG) level, an oxidative DNA damage biomarker originating in urine specimens, significantly decreased (p = 0.007) during co-exposure with GTP for 3 months [30]. Besides, AFB1-albumin adducts (AFB1-AA) and AFB1-mercapturic acid (AFB1-NAC) level in blood and urine specimens of volunteers were compared among 500 and 1000 mg GTP treatment group and control group. This result revealed a reduction of AFB1-AA level, an indicator of AFB1 exposure, for both 500 and 1000 mg GTP treatment groups within 3 months. This reduction was strongly related to dose and duration of GTP exposure (p = 0.049). Furthermore, AFB1-NAC, an indicator of AFB1 elimination activated by phase II metabolism enzymes, significantly increased (p < 0.001) in both treatment groups related to dose and duration of GTP exposure as well

**267**

**2.4 Turmeric**

effectively detoxify oxidative stress [42].

*Modulation of Edible Plants on Hepatocellular Carcinoma Induced by Aflatoxin B1*

no data from one study significantly influenced the final conclusion [25].

bran extract on the prevention of AFB1-induced genotoxicity [39].

Apart from purple rice bran extract, other anthocyanin-rich plants are also studied for their effects on AFB1-induced cytotoxicity. For instance, *Lannea microcarpa,* a tropical African plant, has been studied for its activities against hepatotoxicity, DNA fragmentation, and oxidative stress induced by AFB1. Before exposure to AFB1, animals were pre-exposed with *Lannea microcarpa* extracts for 6 months. Results showed that hepatotoxicity, DNA fragmentation, and oxidative stress was lower in extract-pretreated group when compared to AFB1-treated group [40].

Turmeric is a flowering plant widely used as a food ingredient in South Asia for a long period of time. It has been also applied in pharmacognosy field as a powerful anti-inflammatory resulting from rheumatoid arthritis, bruise, epilepsy, abdominal pain or discomfort, and asthma [41]. An *in vivo* study of turmeric clearly showed the anticancer properties of turmeric on liver, skin, and colorectal cancers. It has a strong potential to inhibit cancer cell growth through stimulating apoptosis and inhibiting phase I metabolism enzymes. It can also stimulate phase II metabolism enzyme activities which play an important role in converting reactive metabolites to excretable forms. Also, turmeric exhibits the antioxidant capacity which can

(p < 0.001). Therefore, it could be summarized that GTP effectively modulated AFB1 biotransformation by inhibition of phase I metabolism enzymes as can be seen from the reduction of AFB1-AA. GTP also has an induction effect to phase II metabolism enzymes which transform AFB1–8,9-epoxide to AFB1-NAC [31].

Furthermore, results from a meta-analysis investigating the effect of green tea extracts on HCC and other liver diseases also showed that regular green tea drinkers had a lower incidence of HCC than nonregular drinkers approximately 26% (R = 0.74, 95% CI = 0.56–0.97, p = 0.027). Although there were some inconsistent

Anthocyanins, members of flavonoid groups, are mostly found in blue, purple, orange, and red vegetables. Anthocyanins in plants play a vital role in attraction of bugs for pollination and insect resistance [32]. Pharmacologically, purple corn extracts have been known for its anti-diabetic and antiadipogenic effects, anti-prostate carcinogenesis, and others [33–35] while blue butterfly pea flower has a definite potential anti-inflammatory effect [36]. Furthermore, anthocyanin-rich plants were shown to protect neurodegenerative and also cardiovascular disease [37].

Purple rice bran (*Oryza sativa* L. var. *indica*) contained flavonoids and anthocyanins approximately 53 and 2 mg/g, respectively. Both compounds were reported to reduce AFB1-induced toxicity, and they were capable of inhibiting mutagenicity in *Salmonella typhimurium* strains TA98 and TA100 [38]*.* In animal model, rats were pre-treated with purple rice bran extracts for a month before exposure to AFB1. Then, the expression of CYP450 including CYP1A2 and CYP3A was investigated; both of them have an identical role in transforming AFB1 to AFB1-epoxide. The results showed that the extracts could not only inhibit the expression of CYP1A2 and CYP3A, but also increase the expression of GST and UGT which encouraged AFB1 excretion. Further in *in vivo* studies, the genotoxicity was evaluated by micronucleus assay, and the result showed lower micronucleus formation in extractpretreated group than AFB1 treated alone, confirming the capability of purple rice

= 80.1%, p = 0.000), no publication bias was detected and

*DOI: http://dx.doi.org/10.5772/intechopen.87296*

results in this study (I2

**2.3 Purple rice**

*Modulation of Edible Plants on Hepatocellular Carcinoma Induced by Aflatoxin B1 DOI: http://dx.doi.org/10.5772/intechopen.87296*

(p < 0.001). Therefore, it could be summarized that GTP effectively modulated AFB1 biotransformation by inhibition of phase I metabolism enzymes as can be seen from the reduction of AFB1-AA. GTP also has an induction effect to phase II metabolism enzymes which transform AFB1–8,9-epoxide to AFB1-NAC [31].

Furthermore, results from a meta-analysis investigating the effect of green tea extracts on HCC and other liver diseases also showed that regular green tea drinkers had a lower incidence of HCC than nonregular drinkers approximately 26% (R = 0.74, 95% CI = 0.56–0.97, p = 0.027). Although there were some inconsistent results in this study (I2 = 80.1%, p = 0.000), no publication bias was detected and no data from one study significantly influenced the final conclusion [25].

### **2.3 Purple rice**

*Phytochemicals in Human Health*

**2.2 Green tea**

glucosinolates have the potential to increase excretion of many carcinogens through glutathione *S*-transferase stimulation. Once the GST was stimulated, carcinogenic-

Green tea, *Camellia sinensis,* is a beverage that contains high contents of phenolic compounds at approximately 30% of dry weight. One of the major phenolic compounds in green tea is catechin, particularly epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG), and epicatechin (EC) [22]. Recent studies have demonstrated the positive effects of green tea on many diseases and adverse human health conditions such as coronary artery disease, oral heath, bone integrity, thermoregulation balance, and kidney stones. Furthermore, an association between green tea consumption and the incidence of many types of cancer has also been reported such as oral and pharynx, esophageal, gastric, colorectal, bladder, prostate, breast, lung, skin, leukemia, pancreatic, and liver cancers [23, 24]. Various research methods including preclinical studies (*in vitro* and *in vivo*), epidemiology, and clinical trial were used to investigate the effect of crude green tea extract or single compound like EGCG on many types of cancer [25]. Overall, an anti-cancer mechanism of green tea extracts against cancer cells was evidently elucidated. Green tea extracts were able to induce apoptosis of cancer cells through inhibiting nuclear factor kappa light chain enhancer of activated B cells (NF-κB) activity and B-cell lymphoma extra-large (Bcl-xL) mRNA expression. Besides, the reduction of angiogenesis of cancer cells was also resulted by green tea extracts through inhibition of vascular endothelial growth factor (VEGF) expression [26]. Previous studies have been reported on several protective ways against AFB1 induced liver cancer from the exposure to catechin compounds and green tea extracts. For example, the reduction of chromosome aberration in rat bone marrow cells was observed after pre-exposure with green tea or EGCG for 24 hours prior to AFB1 [27]. Besides, hepatic nuclear AFB1-DNA binding and glutathione S-transferase placental form (GST-P) positive single hepatocyte, specific markers of hepatocarcinogenic potential in the rat model, were also reduced after pre-exposure with green tea extracts for 2–4 weeks prior to AFB1 [28]. Similarly, the levels of GST-P and γ-glutamyl transpeptidase positive hepatic foci induced by AFB1 and carbon tetrachloride were reduced during pre- or co-treatment with green tea extracts.

Furthermore, the inhibition of hepatocarcinogenesis was also observed [29]. The studies of green tea against AFB1-induced human liver cancer are still currently limited, and most reports have been retrieved from China. As some Chinese commonly consume food contaminated with AFB1, the risk of HCC is higher than other regions. A clinical study demonstrated a protective effect of 500 and 1000 mg/day green tea polyphenol (GTP) on hepatocarcinogenesis in 124 HCC patients who presented with HBsAg and aflatoxin-albumin adducts. Results showed that 8-hydroxydeoxyguanosine (8-OHdG) level, an oxidative DNA damage biomarker originating in urine specimens, significantly decreased (p = 0.007) during co-exposure with GTP for 3 months [30]. Besides, AFB1-albumin adducts (AFB1-AA) and AFB1-mercapturic acid (AFB1-NAC) level in blood and urine specimens of volunteers were compared among 500 and 1000 mg GTP treatment group and control group. This result revealed a reduction of AFB1-AA level, an indicator of AFB1 exposure, for both 500 and 1000 mg GTP treatment groups within 3 months. This reduction was strongly related to dose and duration of GTP exposure (p = 0.049). Furthermore, AFB1-NAC, an indicator of AFB1 elimination activated by phase II metabolism enzymes, significantly increased (p < 0.001) in both treatment groups related to dose and duration of GTP exposure as well

ity and risk of diseases in human were also decreased [21].

**266**

Anthocyanins, members of flavonoid groups, are mostly found in blue, purple, orange, and red vegetables. Anthocyanins in plants play a vital role in attraction of bugs for pollination and insect resistance [32]. Pharmacologically, purple corn extracts have been known for its anti-diabetic and antiadipogenic effects, anti-prostate carcinogenesis, and others [33–35] while blue butterfly pea flower has a definite potential anti-inflammatory effect [36]. Furthermore, anthocyanin-rich plants were shown to protect neurodegenerative and also cardiovascular disease [37].

Purple rice bran (*Oryza sativa* L. var. *indica*) contained flavonoids and anthocyanins approximately 53 and 2 mg/g, respectively. Both compounds were reported to reduce AFB1-induced toxicity, and they were capable of inhibiting mutagenicity in *Salmonella typhimurium* strains TA98 and TA100 [38]*.* In animal model, rats were pre-treated with purple rice bran extracts for a month before exposure to AFB1. Then, the expression of CYP450 including CYP1A2 and CYP3A was investigated; both of them have an identical role in transforming AFB1 to AFB1-epoxide. The results showed that the extracts could not only inhibit the expression of CYP1A2 and CYP3A, but also increase the expression of GST and UGT which encouraged AFB1 excretion. Further in *in vivo* studies, the genotoxicity was evaluated by micronucleus assay, and the result showed lower micronucleus formation in extractpretreated group than AFB1 treated alone, confirming the capability of purple rice bran extract on the prevention of AFB1-induced genotoxicity [39].

Apart from purple rice bran extract, other anthocyanin-rich plants are also studied for their effects on AFB1-induced cytotoxicity. For instance, *Lannea microcarpa,* a tropical African plant, has been studied for its activities against hepatotoxicity, DNA fragmentation, and oxidative stress induced by AFB1. Before exposure to AFB1, animals were pre-exposed with *Lannea microcarpa* extracts for 6 months. Results showed that hepatotoxicity, DNA fragmentation, and oxidative stress was lower in extract-pretreated group when compared to AFB1-treated group [40].

#### **2.4 Turmeric**

Turmeric is a flowering plant widely used as a food ingredient in South Asia for a long period of time. It has been also applied in pharmacognosy field as a powerful anti-inflammatory resulting from rheumatoid arthritis, bruise, epilepsy, abdominal pain or discomfort, and asthma [41]. An *in vivo* study of turmeric clearly showed the anticancer properties of turmeric on liver, skin, and colorectal cancers. It has a strong potential to inhibit cancer cell growth through stimulating apoptosis and inhibiting phase I metabolism enzymes. It can also stimulate phase II metabolism enzyme activities which play an important role in converting reactive metabolites to excretable forms. Also, turmeric exhibits the antioxidant capacity which can effectively detoxify oxidative stress [42].

Curcumin is a major active component of turmeric. It belongs to curcuminoid group and commonly found in 2–8%. Previous *in vivo* studies investigated the effects of turmeric and curcumin on AFB1-induced toxicity, and results showed that turmeric and curcumin decreased AFB1-adduct formation, biomolecule damage, and hepatotoxicity [43–46], and it also inhibited acute toxicity through disturbing the lysis of erythrocytes [47]. During AFB1 metabolism, free radicals generated by AFB1 could be readily inhibited by turmeric and curcumin via decreasing lipid peroxidation and enhancing glutathione content. Likewise, they could activate several antioxidant enzymes such as glutathione peroxidase (GPx), superoxide dismutase (SOD), catalase (CAT), GST, and UGT which play a fundamental role in converting AFB1 to excretable forms [43–46].

Turmeric is found to be capable of reducing both AFB1-induced toxicity and HCC. Besides, it could also stimulate apoptosis of liver cancer cells through a mitochondria-dependent pathway and accumulation of calcium ions within the cells [48]. Turmeric showed the protective effect against AFB1-induced liver cancer in animal model by inhibition of metastasis and growth factor expression related to the progression of angiogenesis [49].

### **2.5 Green vegetables**

Chlorophyll (chla), a main component of green vegetables, consists of a porphyrin ring structure where magnesium is the central atom of the ring. Chla is important for plants' photosynthesis pathway and used as food additives. One of the characteristics of chla is almost insoluble in water while chlorophyllin (CHL), a derivative of chla, is completely soluble. CHL can be transformed into water-soluble form by saponification, a reaction that magnesium central atom is replaced with copper. *In vivo* and clinical studies in pharmacological researches of both chla and CHL revealed that they provided the therapeutic uses such as wound healing, antiinflammation, anti-oxidation, anti-mutagenesis, and anti-carcinogenesis [50, 51].

Previous studies on the protective effects of chla and CHL on AFB1 toxicity indicated that both compounds could reduce absorption of AFB1 from apical to basolateral sides in Caco-2 cell line [52]. Accordingly, a crossover clinical trial demonstrated that chla and CHL exposure could reduce maximum concentration (Cmax) and area under the curves (AUC) of AFB1 compared to untreated group [53]. These findings suggest that chla and CHL have a strong potential to decrease AFB1 absorption. The effects of chla and CHL co-exposure with AFB1 have also been studied in animal model by emphasizing on antioxidant activities. Both bioactive compounds are capable of reducing AFB1 toxicity through enhancing the expression of glutathione level and several antioxidant enzyme activities such as GPx, SOD, and CAT [54].

A recent study investigated the effects of CHL on AFB1-induced hepatotoxicity and incidence of carcinogenesis in animal model. Exposure with CHL reduced hepatotoxicity and incidence of liver cancer [54, 55]. In a clinical study, a randomized controlled trial reported that daily exposure with CHL for 4 months decreased AFB1-N7-guanine level in urine compared to placebo group [56].

Several studies were in agreement that chla and CHL reduce AFB1-induced liver cancer through decreasing AFB1 absorption in digestive tract contributing to the decrease of AFB1 bioavailability. Besides, chla and CHL are the powerful antioxidants which effectively lower AFB1-induced oxidative stress. These two compounds not only reduce hepatotoxicity, but also incidence of liver cancer. Thus, the consumption of green vegetables is one of the alternatives to reduce toxicity caused by consuming AFB1-contaminated foods.

**269**

*Modulation of Edible Plants on Hepatocellular Carcinoma Induced by Aflatoxin B1*

Ginger (*Zingiber officinale* Roscoe) contained high content of phenolic compounds in which 6-gingeerol and 6-shogaol are main constitutions [57]. Ginger plays a critical role as hepatoprotective effects through antioxidant mechanism; for example, liver injury by administration of country-made liquor (CML) and ironinduced nonalcoholic fatty liver disease (NAFLD) [58] and liver cirrhosis induced by carbon tetrachloride [59]. It was also reported to show the protective effects

In in vitro model of AFB1-treated HepG2 cells, ginger extract-pretreated cells exhibited higher percent cell viability and lower intracellular ROS production and DNA strand break when compared to AFB1 treatment alone. In Wistar rats, pretreatment with ginger extract also increased the activities of antioxidant enzymes: GPx, GST, CAT, and SOD, decreased malondialdehyde (MDA) level, and increased reduced glutathione (GSH) content. Co-incubation with ginger extract along with AFB1 also showed a hepatoprotective effect as seen by the lower level of serum enzymes: alanine aminotransferase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP), and lactate dehydrogenase (LDH). Moreover, fat droplets and hepatocyte infiltration with macro-vesicles in liver induced by AFB1 were normalized when pre-treated with ginger extract, clearly showing the effectiveness of

Mechanism of ginger extract to reduce AFB1-induced hepatotoxicity was demonstrated by *in vivo* study. The expression of nuclear factor-E2-related factor 2 (Nrf2), a redox-responsive transcription factor, was increased when pre-treated with ginger extract. Nrf2 was translocated into the nucleus to regulate the antioxidant response element (ARE) which is the promotor of detoxification and antioxidant genes. Moreover, administration of ginger extract induced the expression of heme oxygenase 1 (HO-1) which is associated with the normalization of redox status [57]. Therefore, ginger extract could reduce AFB1-induced hepatotoxicity in both *in vitro* and *in vivo* through antioxidant activities controlled by the function of

*Dialium guineense* is a fruit-bearing tree known as the velvet tamarind. Their bark, leaves, seeds, and fruit showed biological properties such as antimicrobial activities, anti-infectious diseases, and wound-healing [60, 61]. Extract from *Dialium guineense* showed ROS scavenging activities and could normalize the levels of enzyme biomarkers of hepatotoxicity: ALP, AST, and AST induced by AFB1. Furthermore, treatment of velvet tamarind extract before AFB1 exposure increased the antioxidant activities of various enzymes including SOD, GPx, GR, CAT, GSH, and oxidized glutathione (GSSH), decreased lipid peroxidation, protein carbonyl and DNA fragmentation. *In vitro* and *in vivo* experiments have also confirmed the protective effects of velvet tamarind extract against hepatotoxicity induced by AFB1

*Parkia biglobosa,* known as the African locust bean tree (ALBT)*,* is a perennial tree legume growing in West Africa. Several parts of ALBT (bark, leaves, pods,

*DOI: http://dx.doi.org/10.5772/intechopen.87296*

**2.6 Ginger (***Zingiber officinale* **Roscoe)**

ginger on AFB1-induced hepatotoxicity [57].

against AFB1-induced toxicity.

Nrf2 and HO-1.

**2.7 Plants in family Fabaceae**

via antioxidant properties [62].

*2.7.2 Parkia biglobosa*

*2.7.1 Dialium guineense*


**6. Dissolved oxygen levels in nutrient solution**

Maintaining enough dissolved O2 in a nutrient solution in a hydroponic system is crucial for plant health. Oxygen availability to roots grown in soilless culture can become limiting in case O2 demand exceeds O2 supply, inducing a reduction in root growth rate, ion, and water uptake, eventually reducing plant production [84]. Plants grown in hydroponic systems can quickly deplete the dissolved O2 in the nutrient solution resulting in poor root aeration, especially when greenhouse temperatures are high, **Table 5** shows O2 solubility in pure water at different temperatures. Jong et al. [86] noticed that cucumber growth was significantly affected by root-zone aeration. Roosta et al. [87] found improve eggplant growth with rising O2 levels in the nutrient solution in floating hydroponic cultures and higher O2 levels seemed to alleviate signs of ammonium toxicity among the tested plants. Root respiration also decreases when O2 supply in the root environment falls below a critical O2 concentration [88]. The sensitivity of roots to low O2 concentration depends on its effect on mitochondrial respiration because it supplies most of the energy required for root function. Reduction in O2 levels in the nutrient solution could lead to poor roots, an increase in the incidence of diseases and pests, and a reduction in plant growth. Oxygen around a plant's roots affects the beneficial microorganisms that provide protection from pathogens and improve nutrient uptake. Tomato plant roots would be

#### **Table 5.**

*Solubility of oxygen in pure water at various temperatures.*

much more susceptible to Pythium infection if root zone O2 dropped below 2.8 mg/L [89]. Dissolved O2 concentration, is strongly dependent on solution temperature and flow rate near the root zone, as well as on the growth rate of the crop, and may be influenced by the bacterial community present in the solution. The temperature has a direct relationship to the amount of oxygen consumed by the plant and a reverse relationship with dissolved oxygen from the nutrient solution. The consumption of O2 increases when the temperature of the nutrient solution increases. Consequently, it produces an increase in the relative concentration of CO2 in the root environment if the root aeration is not adequate [90]. For overcoming the limited oxygen exchange between the atmosphere and the nutrient solution in static deep water culture hydroponics, the nutrient solution is aerated by an air bubbler connecting with the pump to provide adequate root oxygenation [6]. Roots of loose-leaf lettuce grown in a floating raft hydroponic system were found to have a better condition with oxygen enrichment done in nutrient solution up to aeration pressure of 0.012 mPa and concentration of 600 ppm, with indicators of increasing length and total root surface area [68]. So, it is important to make sure the nutrient solution is properly aerated to maintain enough oxygen for the plant cells found in the root mass since this is crucial to the function of the plant's cells and the microbial world.

#### **7. Nutrient solution management**

An optimized and well-balanced supply of nutrients is a prerequisite for efficient use of the resources by hydroponically grown vegetables, not only to ensure a high yield but also to guarantee the quality of the edible tissues. In hydroponics, because of the limited nutrient-buffering capacity of the system and the ability to make rapid changes, careful monitoring of the system is necessary. The frequency and volume of the nutrient solution applied depends on the type of substrate, the crop and growth stage, the size of the container, the irrigation systems used, and the prevailing climatic conditions. Depending on the stage of plant development, some elements in the nutrient solution will be depleted more quickly than others and as water evaporates from the nutrient solution, the fertilizer becomes more concentrated and can burn plant roots. In hydroponics, nutrient management is very important and must be done as highly efficient as possible to improve productivity without harming the environment.

#### *Nutrient Solution for Hydroponics DOI: http://dx.doi.org/10.5772/intechopen.101604*

Nutrient management included- application the right fertilizers source (e.g., ammonium or nitrate as nitrogen source), balanced nutrient solution according to plants needs and according to plant growth stages and climatic conditions. The main principle of crop nutrient management is to prevent overapplication of nutrients, which prevents loss due to low yield from toxicities of some nutrients resulting from the unnecessary use of fertilizers. It was reported that the strong difference between the ion ratios presented in the nutrient solution and those absorbed by plants led to the accumulation of certain ions in the nutrient solution, which caused an imbalance of mineral elements in the nutrient solution and created more energy to absorb the suitable ions [6]. Recycling exhausted solutions may also represent an efficient strategy to prevent groundwater and environmental pollution. However, the main problem with the reuse of exhausted nutrient solutions is the shortage of some key macro and micronutrients [91] and their increased salinity [92] causing, in turn, problems for crops [93, 94]. Thus, it is very important to develop management practices/tools that reduce salinity in recycled solutions and/or minimize the physiological impact of salinity on plants. The salinity increase could be contrasted by treating the recycled water with appropriate osmotic systems, including forward and reverse osmosis.

In closed hydroponic systems, accumulation of potentially toxic organic compounds released by the roots of cultivated plants may occur and to overcome this issue, several treatment techniques have been proposed for root exudates degradation or removal. However, for the treatment to be effective, it should be able to remove root exudates without interfering with the inorganic mineral nutrients in the solution. As above-mentioned, the regulation of the solution flow rate in hydroponic production affects plant growth, which in turn affects crop yield and quality. The influence of nutrient solution flow rate on plant growth is related to the plants' physical environment. The flow of nutrient solution not only promotes nutrient ion diffusion but also increases the kinetic energy available to plant roots Therefore, adjusting the flow rate can improve plant yield and a reasonable flow pattern must be carefully selected. Because increasing the flow means increasing electricity consumption, it increases the cost of operation. Therefore, it is important to balance plant yield, nutrient management, and energy utilization. According to Baiyin et al. [95], determining the ideal flow rate for hydroponic production may help to increase yield. However, such a determination requires a specific analysis of each crop and growing environment. The hydroponic nutrient solution is the sole source of nutrients to the plant; therefore, it is imperative that a balanced solution, containing all the right plant nutrients, is applied.


**6. Mono-process extraction, bioenergy, and biorefinery**

The circular economy demands the efficient utilization of resources in the production systems and the long-term material use by recycling or remanufacturing [59]. This concept can be correctly applied to the product obtained from biomass processing, such as coffee waste. This material could be a feedstock for a monoprocess extraction, bioenergy production, and biorefining. The first stage of the process design is determining the composition of SCG, which has been shown to be highly dependent on coffee varieties [60–62]. The range of the biochemical composition values obtained is shown in **Table 2**. It is important to consider that SCG has a high quantity of organic compounds such as polyphenols, polysaccharides, amino acids, fatty acids, and minerals.


**2.3. Effects of periodic DFB grating structures in OLEDs**

In this section, we examine light extraction characteristics from OLED devices with 1-D or 2- D DFB grating substrates. The waveguided light is extracted to normal direction by an imprinted low-refractive index layer (1-D DFB grating). Also, electrical characteristics in OLEDs with 2-D hexagonally nano-imprinted periodic structures are investigated to confirm the enhanced light extraction from this device (2-D DFB grating). We review previously reported results in view of light extraction characteristics and electrical characteristics from periodically corrugated OLEDs.

*Optical characterization of corrugated OLEDs with periodic structures (1-D grating)*: Figure 8(a) shows a schematic illustration of the Bragg diffraction process of waveguided light in periodic structures. When waveguided light is incident on the grating structure, the light is reflected by a photonic band gap and simultaneously diffracted in the direction perpendicular to the photonic crystal surface because the Bragg condition is satisfied in this direction. The angle *θ* of the emission direction with respect to the surface normal is governed by the conservation of momentum in the plane of the waveguide [21-24,37,38] given by

$$k\_0 \sin \theta \ = \pm k\_{\text{avg}} \pm k\_g = \pm \frac{2\pi n\_{eff}}{\lambda} \pm m \frac{2\pi}{\Lambda} \tag{7}$$

Effect of Photonic Structures in Organic Light-Emitting Diodes

(8)

Figure 9 shows the angle dependence of EL spectra for the two EL devices with and without the grating structure. For measuring the EL spectra, a detector with a diameter of 5 mm is located 10 cm apart from the device surface. A sharp peak (632 nm) has been observed in the normal direction (*θ* =0°), and a peak splitting has been found to occur by increasing the detection angle because the grating diffracted waveguided light travels in the opposite direction. The wavelengths of the separated two peaks have been measured as a function of the detection angle as shown in Fig. 10(a). The measured wavelength positions agree well

> 2 21 3 2 1 3 32 arcsin sin arcsin sin arcsin sin *n nn n nn*

considering all refractions in PPFVB/glass/air, as shown in Fig. 10(b). This means that extraction angle of Bragg diffracted light is closely related to refractive indices of stacked

Calculated ( )

θ

Calculated ( Measured θ1

**0 5 10 15 20**

**Extraction angle (degrees)**

Calculated ( ) θ3

**Figure 10.** (a) Measured extraction angles of Bragg diffracted light. *θ*1 and *θ*3 denote calculated extraction angles in CYTOP and air, respectively. (b) Schematic illustration for refraction of Bragg diffracted light in each stacked material. 33 Copyright 2008, American Institute of Physics.

To compare the effects of refractive indices of imprinted materials, we have calculated light extraction angles from materials with various refractive indices, as shown in Fig. 11. The wavelength of vertically emitted light is assumed to be 632 nm. According to eq. (8), as the refractive index becomes high, the light extraction angle becomes wider. For *n*=1.80, the extraction angle of light with wavelength of 800 nm is 65°, whereas the total light extraction angle is only 23° for *n*=1.00. In the case of CYTOP (*n*=1.34), the total light extraction angle is

with the lines given by eq. (8) with *θ3*, which is given by

**750 800**

**550**

**(nm)**

(a)

(b)

materials.

– Light Extraction and Polarization Characteristics 75

where *λ* is the wavelength, *k*wg and *k*g are respectively the wavenumbers of the waveguided light and the grating with a period *Λ*, *neff* is the effective refractive index of the waveguide mode, *k0* is the free-space wavenumber of the diffracted light, and *m* is the diffraction order. If *Λ* and *neff* are known, eq. (7) gives the emission angle of extracted light as a function of wavelength for the first-order Bragg diffraction of waveguided light.

**Figure 8.** (a) Schematic illustration of Bragg diffraction of waveguided light. (b) AFM image of patterned azobenzene polymer. 33 Copyright 2008, American Institute of Physics.

**Figure 9.** Angular dependence of electroluminescence spectra from OLED devices with flat (green curve at *θ* =0°) and patterned CYTOP layer. 33 Copyright 2008, American Institute of Physics.

Figure 9 shows the angle dependence of EL spectra for the two EL devices with and without the grating structure. For measuring the EL spectra, a detector with a diameter of 5 mm is located 10 cm apart from the device surface. A sharp peak (632 nm) has been observed in the normal direction (*θ* =0°), and a peak splitting has been found to occur by increasing the detection angle because the grating diffracted waveguided light travels in the opposite direction. The wavelengths of the separated two peaks have been measured as a function of the detection angle as shown in Fig. 10(a). The measured wavelength positions agree well with the lines given by eq. (8) with *θ3*, which is given by

74 Organic Light Emitting Devices

a photonic band gap and simultaneously diffracted in the direction perpendicular to the photonic crystal surface because the Bragg condition is satisfied in this direction. The angle *θ* of the emission direction with respect to the surface normal is governed by the conservation of

> 2 2 sin *eff wg g*

where *λ* is the wavelength, *k*wg and *k*g are respectively the wavenumbers of the waveguided light and the grating with a period *Λ*, *neff* is the effective refractive index of the waveguide mode, *k0* is the free-space wavenumber of the diffracted light, and *m* is the diffraction order. If *Λ* and *neff* are known, eq. (7) gives the emission angle of extracted light as a function of

*k kk m*

**Figure 8.** (a) Schematic illustration of Bragg diffraction of waveguided light. (b) AFM image of

θ **= 0**°

θ **= 3**°

θ **= 5**°

θ **= 1**°

**Figure 9.** Angular dependence of electroluminescence spectra from OLED devices with flat (green curve at *θ* =0°) and patterned CYTOP layer. 33 Copyright 2008, American Institute of Physics.

**500 600 700 800**

**Wavelength (nm)**

patterned azobenzene polymer. 33 Copyright 2008, American Institute of Physics.

**(a.u.)**

**Intensity**

*n*

 (7)

momentum in the plane of the waveguide [21-24,37,38] given by

wavelength for the first-order Bragg diffraction of waveguided light.

0

$$\theta\_3 = \arcsin\left(\frac{n\_2}{n\_3}\sin\theta\_2\right) = \arcsin\left(\frac{n\_2}{n\_3}\sin\left(\arcsin\left(\frac{n\_1}{n\_2}\sin\theta\_1\right)\right)\right) \tag{8}$$

considering all refractions in PPFVB/glass/air, as shown in Fig. 10(b). This means that extraction angle of Bragg diffracted light is closely related to refractive indices of stacked materials.

**Figure 10.** (a) Measured extraction angles of Bragg diffracted light. *θ*1 and *θ*3 denote calculated extraction angles in CYTOP and air, respectively. (b) Schematic illustration for refraction of Bragg diffracted light in each stacked material. 33 Copyright 2008, American Institute of Physics.

To compare the effects of refractive indices of imprinted materials, we have calculated light extraction angles from materials with various refractive indices, as shown in Fig. 11. The wavelength of vertically emitted light is assumed to be 632 nm. According to eq. (8), as the refractive index becomes high, the light extraction angle becomes wider. For *n*=1.80, the extraction angle of light with wavelength of 800 nm is 65°, whereas the total light extraction angle is only 23° for *n*=1.00. In the case of CYTOP (*n*=1.34), the total light extraction angle is

35°. Thus nano-imprinted CYTOP layer can extract waveguided light with high directionality. Such characteristics provide an advantage for small- or medium-size OLEDs, which are mainly viewed from the forward direction [39].

Effect of Photonic Structures in Organic Light-Emitting Diodes

*Electrical characterization of corrugated OLEDs with periodic structures (2-D grating)*: The current–voltage (I-V) characteristics of an EL device with a 2-D grating (2-D grating device) has been measured and compared with those of an EL device without grating (non-grating device). The 2-D grating device shows a higher current level compared to the non-grating device, as shown in Fig. 13(a). Both EL devices show a power-law dependence of *I~V6-7* over a large current and voltage range. Because of large trap concentration and low mobility in organic semiconductors, the carrier transport in OLEDs is trap-charge-limited current

**With 2-D grating**

**1 10**

**Voltage (V)**

**012345**

**Voltage (V) Voltage (V)**

**Without 2-D grating**

**Without 2-D grating**

**Vtr**

**Figure 13.** (a) Current-voltage plot measured from a 2-D grating and non-grating devices. (b) Magnified current-voltage plots in low voltage region.35 Copyright 2008, The Japan Society of Applied

current must satisfy TCLC conduction more quickly.

observed. In this case, the current density *J* is described by

One may intuitively think that higher current effect in 2-D grating devices is simply due to the increase of interface contact area by corrugation between electrode and organic semiconductors. However, this cannot explain the increase of transition voltage (*Vtr*) at which the conduction model changes from ohmic to TCLC, as indicated by two arrows in Fig. 13(a). If the increase in the interface contact area is a major effect, *Vtr* in the grating device must be shifted to a voltage lower than that of the non-grating device because higher

**With 2-D grating**

At low voltages, low-mobility ohmic conduction via thermally generated free charge is

Physics.

(TCLC) [40], which is known to show power law dependence.

**m2**

(a)

**)**

**density (A/**

**d**

**A/cm2**

**A**

**nt density (**

**Curre**

(b)

**)**

**10-3 c**

**10**

**10-5**

**10-7**

**(x 10-5)**

**10-6 Current**

**10-4**

– Light Extraction and Polarization Characteristics 77

**Figure 11.** Calculated extraction angles in imprinted materials with various refractive indices as a function of wavelength. 33 Copyright 2008, American Institute of Physics.

The effect of a grating on normally-directed EL has been observed by collecting EL spectra between ±18.4°, as shown in Fig. 12. The enhancement of EL spectra in the device with patterned CYTOP layer has been observed over the wavelength range from 540 nm to 728 nm. However, it should be noted that the highest EL intensity is observed only around 650 nm, whereas vertically directed emission peak position is 632 nm. This results from different transmittance of ITO at various wavelengths as shown in Fig. 12. Because the wavelength of the highest EL intensity is closely related to both natural fluorescence and waveguide absorption in ITO layer, the light can be extracted more efficiently due to the high transmittance and fluorescence at 650 nm. Hence, the grating effect is higher in longer wavelength region which has higher transmittance. If ITO with high transparency is possible to be deposited at room temperature, the grating effect of CYTOP with high transmittance will be increased.

**Figure 12.** Overall EL spectra within ±18.4° from OLEDs with flat and patterned CYTOP layers. Two dotted lines show transmittance of CYTOP/Glass and ITO/CYTOP/Glass, respectively.33 Copyright 2008, American Institute of Physics.

*Electrical characterization of corrugated OLEDs with periodic structures (2-D grating)*: The current–voltage (I-V) characteristics of an EL device with a 2-D grating (2-D grating device) has been measured and compared with those of an EL device without grating (non-grating device). The 2-D grating device shows a higher current level compared to the non-grating device, as shown in Fig. 13(a). Both EL devices show a power-law dependence of *I~V6-7* over a large current and voltage range. Because of large trap concentration and low mobility in organic semiconductors, the carrier transport in OLEDs is trap-charge-limited current (TCLC) [40], which is known to show power law dependence.

76 Organic Light Emitting Devices

transmittance will be increased.

American Institute of Physics.

35°. Thus nano-imprinted CYTOP layer can extract waveguided light with high directionality. Such characteristics provide an advantage for small- or medium-size OLEDs,

**0 10 20 30 40 50 60 70**

**n=1.00, d=423nm n=1.50, d=363nm**

**n=1.80, d=334nm n=1.34, d=380nm**

> **0.8 1.0**

> **0.2 0.4 0.6**

> **0.0**

**ITO/PPFVP/Glass**

ITO/CYTOP/Glass

**PPFVB/Glass**

CYTOP/Glass

**n**

**Transmittan**

**ce**

**Figure 11.** Calculated extraction angles in imprinted materials with various refractive indices as a

The effect of a grating on normally-directed EL has been observed by collecting EL spectra between ±18.4°, as shown in Fig. 12. The enhancement of EL spectra in the device with patterned CYTOP layer has been observed over the wavelength range from 540 nm to 728 nm. However, it should be noted that the highest EL intensity is observed only around 650 nm, whereas vertically directed emission peak position is 632 nm. This results from different transmittance of ITO at various wavelengths as shown in Fig. 12. Because the wavelength of the highest EL intensity is closely related to both natural fluorescence and waveguide absorption in ITO layer, the light can be extracted more efficiently due to the high transmittance and fluorescence at 650 nm. Hence, the grating effect is higher in longer wavelength region which has higher transmittance. If ITO with high transparency is possible to be deposited at room temperature, the grating effect of CYTOP with high

**Collecting**

**angle (18.4**°)

**0 10 20 30 40 50 60 70**

**Extraction angle (degree)**

**Figure 12.** Overall EL spectra within ±18.4° from OLEDs with flat and patterned CYTOP layers. Two dotted lines show transmittance of CYTOP/Glass and ITO/CYTOP/Glass, respectively.33 Copyright 2008,

**Grating**

**No grating**

**500 600 700 800**

**gratingWavelength (nm)**

function of wavelength. 33 Copyright 2008, American Institute of Physics.

**800 1000**

> **200 400 600**

> > **0**

**u.)**

**Intensity (a.**

which are mainly viewed from the forward direction [39].

**750**

**700**

**600**

**550 Wa**

**650**

**m)**

**m**

**velength (n**

**v**

**800**

**Figure 13.** (a) Current-voltage plot measured from a 2-D grating and non-grating devices. (b) Magnified current-voltage plots in low voltage region.35 Copyright 2008, The Japan Society of Applied Physics.

One may intuitively think that higher current effect in 2-D grating devices is simply due to the increase of interface contact area by corrugation between electrode and organic semiconductors. However, this cannot explain the increase of transition voltage (*Vtr*) at which the conduction model changes from ohmic to TCLC, as indicated by two arrows in Fig. 13(a). If the increase in the interface contact area is a major effect, *Vtr* in the grating device must be shifted to a voltage lower than that of the non-grating device because higher current must satisfy TCLC conduction more quickly.

At low voltages, low-mobility ohmic conduction via thermally generated free charge is observed. In this case, the current density *J* is described by

$$J = q\mu\_n n\_0 V / d\_{t'} \tag{9}$$

Effect of Photonic Structures in Organic Light-Emitting Diodes

Even though the depth of patterned shape is only 50 nm, the 2-D grating device does not show any breakdown during applying voltage. Generally thin EL devices can easily suffer from breakdowns because the internal field distribution is very sensitive to interface roughness and dust particles. It is therefore very important that the patterned electrode shape must be optimized for the stability of EL devices. Otherwise, the patterned electrode may result in worse device condition without realizing any high light extraction efficiency. Because of this reason, one should use those patterned electrode structures which give minimal 'partial reduction thickness of organic layers'. This means that if the field distribution between cathode and anode is uniform, the possibility of breakdown may be reduced even when the depth of patterned shape is high. For studying the effect of the shape of patterned electrodes, we have calculated the static field distribution in EL devices for patterned electrodes of square and sinusoidal shapes. Although the light is diffracted by 500-nm-pitched lines, which has the same width as the interfered periodicity of the two Ar+ laser beams (Fig. 6(b)), the electric field distribution is related to the distance between closest protrusions. Hence the distance used for the calculation is 580 nm. (See Fig. 14(c)). As shown in Fig. 14(a), a high electric field gets localized at the edges of square-shaped cathode and anode electrodes. However, if the patterned electrodes are of sinusoidal shapes the field distribution becomes almost uniform. Figure 14(b) shows static field distribution in sinusoidal-shaped electrode. Note that we use different ranges of relative field intensity in Fig. 14(a) and (b) to clearly visualize the field distribution as color variations. Although the field is concentrated in the intermediate regions between the top and bottom of the patterned electrodes (see Fig. 14(b)), the field distribution becomes much more uniform compared with the case of Fig. 14(a). Figure 14(d) represents the depth profile of a patterned azobenzene film obtained along a red line in the AFM image shown in Fig. 14(c). The shape at the upper region is approximated as sinusoidal. This shape results in no breakdown of 2-

Next, we describe the relationship among the reduction of thicknesses, current efficiency, and diffraction effects. Figure 15(a) displays the external current efficiency versus current density. In the 2-D grating device, a higher efficiency is obtained in a high current density region. However, below a current density of 3×10-5A/cm2, the efficiency of the non-grating device is found to be slightly higher than that of the 2-D grating device, as shown in Fig. 15(b). How can we explain this? As mentioned above, the major difference between a 2-D grating device and a non-grating device is in *RB* or effective thickness of the bulk layer; i.e., *RB* is lower and the layer is thinner in the 2-D grating device than that in the non-grating device. Hence, we should discuss the dependence of current efficiency on the emitter thickness [41]. For this purpose, the recombination probability (*Prec*), which is directly proportional to the EL yield, is considered. *Prec* is defined by the ratio of the recombination

/ 1/ 1 / *rec t t rec rec t P*

This gives *P*rec = 1 when τrec/τt=0 and *P*rec decreases with increasing τrec/τt. The thickness

  (11)

D grating devices even though leakage current is high.

time *τrec* and the transit time *τt* of the charge carriers as:

dependence in t comes only from:

 – Light Extraction and Polarization Characteristics 79

where *q* is the electronic charge, *μn* is electron mobility, *n0* is a thermally generated background free charge density, *V* is the applied voltage, and *dt* is the organic layer thickness. In order to find what induces the low voltage ohmic current, we have examined the *I-V* plot in the low voltage range. According to Fig. 13(b), the 2-D grating device shows a higher ohmic current than that of the non-grating device. This means that the 2-D grating device has a lower total resistance *Rtotal* which is a sum of junction resistance (*RJ*), bulk resistance (*RB*) of organic layers and electrode resistance (*REL*) and is given by:

$$R\_{total} = R\_f + R\_B + R\_{EL} \tag{10}$$

Here the ohmic resistance induced by Al and Au (*REL*) and the junction resistance (*RJ*) induced by interfacial barrier between electrode and organic layer are the same in both samples. Hence *RB* in the 2-D grating device must be smaller than that in the non-grating device. This result may be understood from the concept of 'partial reduction thickness of organic layers' proposed by Fujita *et al*. [27,28]. They have observed improved electroluminescence from a corrugated ITO where the reduction of thickness of organic layers is effectively induced by each edge of Al and ITO square-shape patterned electrodes shown as black areas in Fig. 14(a). At the edge of each patterned electrode, a higher electric field develops (See Fig. 14 (a)) and this results in reduction of operating voltage. Thus, the increased low voltage current in the 2-D grating device may be explained due to the lower bulk resistance (*RB*) and hence the lower total serial resistance.

**Figure 14.** Calculated static field distribution between (a) square- and (b) sinusoidal-shape patterned electrodes. (c) AFM image of a patterned UV epoxy layer. (d) Depth profile along a red line in (c).35 Copyright 2008, The Japan Society of Applied Physics.

Even though the depth of patterned shape is only 50 nm, the 2-D grating device does not show any breakdown during applying voltage. Generally thin EL devices can easily suffer from breakdowns because the internal field distribution is very sensitive to interface roughness and dust particles. It is therefore very important that the patterned electrode shape must be optimized for the stability of EL devices. Otherwise, the patterned electrode may result in worse device condition without realizing any high light extraction efficiency. Because of this reason, one should use those patterned electrode structures which give minimal 'partial reduction thickness of organic layers'. This means that if the field distribution between cathode and anode is uniform, the possibility of breakdown may be reduced even when the depth of patterned shape is high. For studying the effect of the shape of patterned electrodes, we have calculated the static field distribution in EL devices for patterned electrodes of square and sinusoidal shapes. Although the light is diffracted by 500-nm-pitched lines, which has the same width as the interfered periodicity of the two Ar+ laser beams (Fig. 6(b)), the electric field distribution is related to the distance between closest protrusions. Hence the distance used for the calculation is 580 nm. (See Fig. 14(c)). As shown in Fig. 14(a), a high electric field gets localized at the edges of square-shaped cathode and anode electrodes. However, if the patterned electrodes are of sinusoidal shapes the field distribution becomes almost uniform. Figure 14(b) shows static field distribution in sinusoidal-shaped electrode. Note that we use different ranges of relative field intensity in Fig. 14(a) and (b) to clearly visualize the field distribution as color variations. Although the field is concentrated in the intermediate regions between the top and bottom of the patterned electrodes (see Fig. 14(b)), the field distribution becomes much more uniform compared with the case of Fig. 14(a). Figure 14(d) represents the depth profile of a patterned azobenzene film obtained along a red line in the AFM image shown in Fig. 14(c). The shape at the upper region is approximated as sinusoidal. This shape results in no breakdown of 2- D grating devices even though leakage current is high.

78 Organic Light Emitting Devices

0 / , *n t J q nV d*

where *q* is the electronic charge, *μn* is electron mobility, *n0* is a thermally generated background free charge density, *V* is the applied voltage, and *dt* is the organic layer thickness. In order to find what induces the low voltage ohmic current, we have examined the *I-V* plot in the low voltage range. According to Fig. 13(b), the 2-D grating device shows a higher ohmic current than that of the non-grating device. This means that the 2-D grating device has a lower total resistance *Rtotal* which is a sum of junction resistance (*RJ*), bulk

Here the ohmic resistance induced by Al and Au (*REL*) and the junction resistance (*RJ*) induced by interfacial barrier between electrode and organic layer are the same in both samples. Hence *RB* in the 2-D grating device must be smaller than that in the non-grating device. This result may be understood from the concept of 'partial reduction thickness of organic layers' proposed by Fujita *et al*. [27,28]. They have observed improved electroluminescence from a corrugated ITO where the reduction of thickness of organic layers is effectively induced by each edge of Al and ITO square-shape patterned electrodes shown as black areas in Fig. 14(a). At the edge of each patterned electrode, a higher electric field develops (See Fig. 14 (a)) and this results in reduction of operating voltage. Thus, the increased low voltage current in the 2-D grating device may be explained due to the lower

**Figure 14.** Calculated static field distribution between (a) square- and (b) sinusoidal-shape patterned electrodes. (c) AFM image of a patterned UV epoxy layer. (d) Depth profile along a red line in (c).35

resistance (*RB*) of organic layers and electrode resistance (*REL*) and is given by:

bulk resistance (*RB*) and hence the lower total serial resistance.

Copyright 2008, The Japan Society of Applied Physics.

(9)

*R RRR total J B EL* (10)

Next, we describe the relationship among the reduction of thicknesses, current efficiency, and diffraction effects. Figure 15(a) displays the external current efficiency versus current density. In the 2-D grating device, a higher efficiency is obtained in a high current density region. However, below a current density of 3×10-5A/cm2, the efficiency of the non-grating device is found to be slightly higher than that of the 2-D grating device, as shown in Fig. 15(b). How can we explain this? As mentioned above, the major difference between a 2-D grating device and a non-grating device is in *RB* or effective thickness of the bulk layer; i.e., *RB* is lower and the layer is thinner in the 2-D grating device than that in the non-grating device. Hence, we should discuss the dependence of current efficiency on the emitter thickness [41]. For this purpose, the recombination probability (*Prec*), which is directly proportional to the EL yield, is considered. *Prec* is defined by the ratio of the recombination time *τrec* and the transit time *τt* of the charge carriers as:

$$P\_{rec} = \ \tau\_t \ / \ \left(\tau\_t + \tau\_{rec}\right) = 1 / \left(1 + \tau\_{rec} \ / \ \tau\_t\right) \tag{11}$$

This gives *P*rec = 1 when τrec/τt=0 and *P*rec decreases with increasing τrec/τt. The thickness dependence in t comes only from:

$$
\pi\_t = \left. d\_t \right| \left. \mu \right| \mathbf{F}\_t \tag{12}
$$

Effect of Photonic Structures in Organic Light-Emitting Diodes

**Figure 16.** (a) Schematic illustration of diffraction of the guided light. (b) Schematic illustration of the angle range for total reflection and diffraction at 500 nm wavelength. (c) The diffraction limit of incidence angle θ1 for the first diffraction as a function of wavelength. 35 Copyright 2008, The Japan

light to an angle below the critical angle (61°) can be emitted due to the total internal reflection. However, in grating devices, the incident light within the angle range between *θ1* and 90° is diffracted and then emitted at an angle between *θ2* and -90°. For example, in the case of a light with 500 nm wavelength, *θ1* and *θ2* are 0° and 7.6°, respectively. This means that the incident light within the angle range between 0° and 90° can be emitted at an angle

Society of Applied Physics.

– Light Extraction and Polarization Characteristics 81

where *dt* is the emitter layer thickness, the carrier mobility, and *F* the applied electric field operating on the sample. According to eqs. (11) and (12), at a given electric field, increasing emitting layer thickness will increase *τt* and hence *Prec*. Employing this theory, 2-D grating device must show lower current efficiency due to the short transit time by reduction of thickness.

**Figure 15.** (a) Extracted current efficiency against current density measured from a 2-D grating and non-grating devices. (b) Magnified extracted efficiency vs current density in low current density region. 35 Copyright 2008, The Japan Society of Applied Physics.

It should be noted, however, that a higher current efficiency in the 2-D grating device increases even though the non recombined current is higher. The enhanced current efficiency in the 2-D grating device can be explained as follows. First, the waveguided light propagating along the in-plane direction of the device is emitted to the surface direction by Bragg diffraction in the 2-D grating device. Figure 16(a) shows how the diffracted light can be extracted by Bragg diffraction in a 1-D grating sample for simple consideration. If the light incident on a material with the refractive index of *n2* from that of *n1*, the diffraction condition is given by

$$
\hbar \, m \mathcal{X} = d\_c (n\_1 \sin \theta\_1 - n\_2 \sin \theta\_2) \tag{13}
$$

where *d*c is a periodic distance and *m* is a diffraction order. Because the refractive indices are *n1*=1.7 and *n2*=1.5 in EL layer and epoxy/glass, respectively, the 1st-order diffracted light (*m* = 1) can be emitted, as shown in Fig. 16(b) and (c). In flat devices without grating, only EL Effect of Photonic Structures in Organic Light-Emitting Diodes – Light Extraction and Polarization Characteristics 81

80 Organic Light Emitting Devices

thickness.

/ , *t t*

where *dt* is the emitter layer thickness, the carrier mobility, and *F* the applied electric field operating on the sample. According to eqs. (11) and (12), at a given electric field, increasing emitting layer thickness will increase *τt* and hence *Prec*. Employing this theory, 2-D grating device must show lower current efficiency due to the short transit time by reduction of

**1.0 Without 2-D grating**

**Figure 15.** (a) Extracted current efficiency against current density measured from a 2-D grating and non-grating devices. (b) Magnified extracted efficiency vs current density in low current density region.

It should be noted, however, that a higher current efficiency in the 2-D grating device increases even though the non recombined current is higher. The enhanced current efficiency in the 2-D grating device can be explained as follows. First, the waveguided light propagating along the in-plane direction of the device is emitted to the surface direction by Bragg diffraction in the 2-D grating device. Figure 16(a) shows how the diffracted light can be extracted by Bragg diffraction in a 1-D grating sample for simple consideration. If the light incident on a material with the refractive index of *n2* from that of *n1*, the diffraction

1122 ( sin sin ) *m dn n c*

where *d*c is a periodic distance and *m* is a diffraction order. Because the refractive indices are *n1*=1.7 and *n2*=1.5 in EL layer and epoxy/glass, respectively, the 1st-order diffracted light (*m* = 1) can be emitted, as shown in Fig. 16(b) and (c). In flat devices without grating, only EL

  (13)

35 Copyright 2008, The Japan Society of Applied Physics.

condition is given by

**With 2-D grating**

**0.0 5.0x10-4 1.0x10-3 1.5x10-3 0.0**

**With 2-D grating**

**Current density (A/cm2**

**0.0 4.0x10-5 8.0x10-5**

**Current density (A/cm2**

**)**

**Without 2-D grating**

**)**

*d F* (12)

**1.5**

**0 5**

**1.0**

**0.5 ent efficienc**

**0.0**

**cy (cd/A)**

**Curr**

**e**

(b)

**0.5Curren**

**nt efficiency**

**2.0 y (cd/A)**

(a)

**Figure 16.** (a) Schematic illustration of diffraction of the guided light. (b) Schematic illustration of the angle range for total reflection and diffraction at 500 nm wavelength. (c) The diffraction limit of incidence angle θ1 for the first diffraction as a function of wavelength. 35 Copyright 2008, The Japan Society of Applied Physics.

light to an angle below the critical angle (61°) can be emitted due to the total internal reflection. However, in grating devices, the incident light within the angle range between *θ1* and 90° is diffracted and then emitted at an angle between *θ2* and -90°. For example, in the case of a light with 500 nm wavelength, *θ1* and *θ2* are 0° and 7.6°, respectively. This means that the incident light within the angle range between 0° and 90° can be emitted at an angle

in the range between 7.6° and -90°. It should be noted that an incident light within 61°~90° cannot be emitted in flat devices without a grating. In other words, the light diffracted from the incidence angle in the range between 61° and 90° contributes to additional light extraction in 2-D grating devices obtained, resulting in an increase in the of light output.

Effect of Photonic Structures in Organic Light-Emitting Diodes

**Figure 17.** AFM analysis of buckling pattern. (a) Buckled structure formed by a 10-nm-thick Al layer. (b),(c) Buckled structures formed by deposition of a 10-nm-thick Al layer twice and three times, respectively. Resin layers imprinted with a buckled PDMS replica were used for measurement. Inset: FFT patterns of each image. (d) Power spectra from FFTs as a function of wavelength for buckled patterns obtained with deposition of a 10-nm-thick Al layer once (black), twice (red) and three times

The observation that the FFT ring patterns are of similar size indicates that the characteristic wavelength does not change after redeposition. Moreover, the FFT ring patterns after multiple deposition processes display more diffuse patterns, indicating a broader distribution. The power spectra in Fig. 17(d) represent the unchanged peak wavelengths at ~410 nm and the broader distributions in the long wavelength side for the multiple depositions. In addition, the surface area ratio after deposition twice and three times significantly increases from ~1.4% to ~9.0% and 11.3% corresponding to depths of 40–70 nm

The devices with buckling show higher current density (*J*) and luminance (*L*) than those without buckling and a device with triple buckling shows higher *J* and *L* than that with only double buckling (Fig. 18(a)). It has been reported that the larger *J* in the corrugated device mainly results from a stronger electric field because of the partially reduced organic layer thickness in the intermediate region between the peak and valley of the sinusoidal patterned gratings [27,35]. Measurements have also been made on devices without buckling but with the organic layer thickness decreased by 20% and 40%. As mentioned in 2.3, current density (*J*) for these devices is shown by dotted and dashed curves in Fig. 18. The current density in the device with triple buckling lies between that in the reference devices and in devices with thinner organic layers. This suggests that the thickness of the organic layers on buckling is partially reduced by ~20–40%. In the devices with double, triple and without buckling, the

(blue).36 Copyright 2010, Nature Publishing Group.

and 50–70 nm, respectively.

– Light Extraction and Polarization Characteristics 83

Another aspect of enhancing the light extraction in a 2-D grating device is by recovering the quenched light coupled with surface plasmon mode. This effect can be observed in an Alq3 based system because the excitons have no preferred orientation in an Alq3 layer, whereas conjugated polymer systems show a lower effect because the dipole moments lie in the plane of the film due to spin casting. Hobson *et al*. [42] have found that a further recovery of the trapped light can be obtained by the surface plasmon with the help of a periodic grating formed on substrate particularly in Alq3-based EL devices. This effect can also explain the increased current efficiency in Alq3-based EL devices because the corrugation remains intact on the Al electrode layer.


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## Meet the editors

Dr. Mattia Bartoli's research output includes 82 published peer-reviewed papers in top journals. During his time at the Biorefinery Research Group hosted by the University of Alberta, which develops new materials and new technologies, he worked closely with ForgeHydrocarbon a spin-off company focusing on innovative lipid-to-hydrocarbon technology for renewable hydrocarbon production. In 2018, he joined the Car-

bon Group, hosted by the Polytechnic of Turin, Italy, where he studied the production and use of carbon from the thermochemical conversion of waste streams for materials science applications. He is particularly interested in advanced materials such as carbon nanodots and bismuth-based materials for biological and electrochemical applications. Since 2021, Dr. Bartoli has been working on CO2 electrochemical and thermochemical conversion at the Center for Sustainable Future Technologies - CSFT@POLITO.

Mauro Giorcelli, Ph.D., is a professor of applied physics and a researcher in biochar materials. He is a member of the Carbon Group in the Department of Applied Science and Technologies (DISAT) at the Polytechnic of Turin, Italy. His main research interests are the morphological, electrical and mechanical characterizations and applications of carbon-based materials and composites. He has over 100 publications in international

journals and has been an invited speaker at several conferences. Mauro Giorcelli has recently been a guest researcher at the University of Ontario Institute of Technology in Oshawa, Ontario. He also collaborates with several international universities and research centers.

Alberto Tagliaferro obtained his degree in nuclear engineering and his Ph.D. in physics at the Polytechnic of Turin. He is an Associate Professor in the Materials Science and Chemical Engineering Department at the Polytechnic of Turin. He is head of the Carbon Group, a research group founded in 2002. His research interests have moved in recent years to biochar production and applications. He is Chair Adjunct Professor at

the University of Ontario Institute of Technology and editor of *Critical Reviews in Environmental Science and Technology* (CREST) by Taylor and Francis, *Reviews on Advanced Materials Science* by De Gruyter, and *Micromachines* by MDPI. He is Chair of the Education Committee of IUVSTA (International Union for Vacuum Science, Technique and Applications).

### Contents

#### **Chapter 15 335**

Applications and Data Analysis Using Bayesian and Conventional Statistics in Biochar Adsorption Studies for Environmental Protection *by Obey Gotore, Tirivashe Phillip Masere, Osamu Nakagoe, Vadzanayi Mushayi, Ramaraj Rameshprabu, Yuwalee Unpaprom and Tomoaki Itayama*

#### **Chapter 16 355**

PAHs, PCBs and Environmental Contamination in Char Products *by Karl Williams, Ala Khodier and Peter Bentley*


**Magda Pál, Tibor Janda, Imre Majláth and Gabriella Szalai \***

Agricultural Institute, Centre for Agricultural Research, 2462 Martonvásár, Brunszvik 2, Hungary<EMAIL_ADDRESS>(M.P<EMAIL_ADDRESS>(T.J<EMAIL_ADDRESS>(I.M.) **\*** Correspondence<EMAIL_ADDRESS>
Received: 13 February 2020; Accepted: 10 March 2020; Published: 12 March 2020

**Abstract:** The exposure of plants to non-lethal low temperatures may increase their tolerance to a subsequent severe chilling stress. To some extent, this is also true for cold-sensitive species, including maize. In the present work, based on our previous microarray experiment, the differentially expressed genes with phenylpropanoid pathways in the focus were further investigated in relation to changes in certain phenolic compounds and other plant growth regulators. Phenylalanine ammonia lyase (PAL) was mainly activated under limited light conditions. However, light-induced anthocyanin accumulation occurred both in the leaves and roots. Chilling stress induced the accumulation of salicylic acid (SA), but this accumulation was moderated in the cold-acclimated plants. Acclimation also reduced the accumulation of jasmonic acid (JA) in the leaves, which was rather induced in the roots. The level of abscisic acid (ABA) is mainly related to the level of the stress, and less indicated the level of the acclimation. The highest glutathione (GSH) amount was observed during the recovery period in the leaves of plants that were cold acclimated at growth light, while their precursors started to accumulate GSH even during the chilling. In conclusion, different light conditions during the cold acclimation period differentially affected certain stress-related mechanisms in young maize plants and changes were also light-dependent in the root, not only in the leaves.

**Keywords:** acclimation; antioxidants; chilling; phenylpropanoid pathway; salicylic acid; *Zea mays*