Degradation of Green Tea Catechins in Tea Drinks - Assignment Example

? 6 October s I. Degradation of Green Tea Catechins in Tea Drinks (Chen, Zhu, Tsang and Huang 477-482) The aim of this research was to investigate the degradation of Green tea catechins (GTC) such as epicatechin (EC), epigallocatechin (EGC), epicatechin gallate (ECG) and epigallocatechin gallate (EGCG) under various conditions to which they are usually exposed to, during processing and production of canned and bottled tea drinks. This study is significant because it studies the effect of processing conditions on GTC content. It is important to conserve the GTC content of tea during processing to retain its beneficial effects. Results of the study reveal that the GTC content of processed tea is significantly low compared to traditionally prepared tea. While a cup of traditionally brewed tea contains 400-500 mg of GTC, processed tea contains only 3-60 mg GTC. GTC is stable at room temperature. About 10-15%, GTC is lost when tea is heated up to 98 ?C for 15-30 minutes, with additional 5% loss on prolonged heating. Autoclaving at 120 ?C for 20 minutes, which is yet another step during processing, leads to a loss of 23% GTC. This loss is directly proportional to the pH of the medium. Furthermore, about 80% of the GTC content is degraded in a buffer medium of pH 6. The stability and shelf life of GTC is also found to be dependent on pH content in the absence of other ingredients. Half of the GTC content is lost within 3 months at a pH below 4.5. Sucrose has no effect on the stability of GTC while citric acid leads to a faster degradation. Ascorbic acid has a protective effect in the first month after which it accelerates the degradation. In addition, the results also reveal that at high temperatures, EGCG undergoes epimerization to form GCG. This explains the contrasting GCG content between traditionally prepared tea and processed tea, wherein, the GCG content is higher by 45% in processed tea. Overall, it can be concluded that GTC degrades easily at high temperature and pH, and that the stability of GTC depends on the presence of other ingredients. Further studies that focus on the effect of each ingredient present in processed tea on the stability and speed of degradation of GTC are required. II. Coffee and Green Tea as a Large Source of Antioxidant Polyphenols in the Japanese Population (Fukushima et al 1253-1259) The objective of this study was to evaluate the total consumption of polyphenols by Japanese people. Polyphenols are well known for their antioxidant activity and beverages are a major source of polyphenols in Japan. The findings of this study suggest that an individual per day consumes an average of 853 mg of polyphenols. The largest source of polyphenols in the Japanese population is coffee, which provides 200 ml of polyphenols in every 100 mL. The average polyphenol consumption through coffee is found to be 426 mg/day. The second largest source of polyphenol is Green tea, which contributes up to 292 mg polyphenols/day. Thus, coffee and green teas constitute up to 70% of the total beverage consumption and are the largest sources of polyphenols. Among fruits and vegetables, satsuma oranges and onions are the most consumed and provided 9 and 4 mg of polyphenols, respectively, per day. Cacao mass (chocolate) and black pepper contribute about 0.8 g and 0.2 g polyphenols per day. Measurement of the antioxidant activities correlates well with the total polyphenol content of all the tested consumables, suggesting that the in vitro antioxidant activities are proportional to the total polyphenol quantities. Future studies will have to examine whether in vivo antioxidant properties of these polyphenols correlate well with those observed in vitro. III. Content of Potentially Anticarcinogenic Flavonoids of Tea Infusions, Wines, and Fruit Juices (Hertog, Hollman, and Putte 1242-1246) This study attempted to evaluate the concentrations of various anti-carcinogenic flavonoids in beverages such as tea, wines and fruit juices. The study found that myricetin concentration is the highest compared to all other flavonoids in grape juice and wine, except for the red Californian wine and the red Chianti in which quercetin concentration is the highest. Among wines, Italian Chianti wines have the highest levels of flavonoids. In fruit juices, quercetin is the only flavonoid found and tomato juice has the highest flavonoid content among fruit juices. Beer and coffee do not have any flavonoids while chocolate milk has low concentrations of only quercetin. Moreover, quercetin is the only predominant flavonoid found in tea. Another significant finding is that the flavonoid levels of black tea prepared from loose leaves are low. Increase in brewing time of black tea up to ten minutes increases the flavonoid content; however, this amount is fairly insignificant. Furthermore, flavonoid content increases non-linearly with increase in the amount of tea leaves used for brewing. Grinding of tea leaves before brewing also raises the quercetin content by about 40%. In addition, tea bags are found to yield higher flavonoid content than loose tea leaves. Future studies should investigate the beneficial effect of these flavonoids on the risk of cancer and other chronic diseases. IV. Effects of Infusion Time and Addition of Milk on Content and Absorption of Polyphenols from Black Tea (Kyle et al 4889-4894) The variation in bioavailability of polyphenols present in black tea with increase in infusion time and the addition of milk was assessed in this study. The research reveals that the release of phenols and catechins during infusion is similar in different brands of tea. The findings further suggest that an increase in infusion time of tea leads to an increase in the release of phenols, catechins and anti-oxidants up to seven minutes of boiling, after which it has no further effect. Increase in phenol content with infusion time is also found to be influenced with the duration and the intensity of stirring, the size of leaves used and the porosity of the tea bag. Addition of milk has no effect on the anti-oxidant levels found in black tea. Black tea is found to have high concentrations of polyphenols and is associated with a 10% increase in the plasma antioxidant potential within 80 minutes of consumption. Consuming two cups of black tea every day increases the total plasma phenols and catechins along with flavonoids such as quercetin and kaempferol. Increase in infusion time of black tea increases absorption of polyphenols by the body, and addition of milk does not influence this effect. Future studies that investigate the effects of other variations in brewing methods and consumption frequencies on the bioavailability of polyphenols are warranted. V. Polycyclic Aromatic Hydrocarbons: Pollution and Source Analysis of a Black Tea (Lin and Zhu 8268?8271) This study investigated the levels of sixteen polycyclic aromatic hydrocarbons (PAHs) at various stages during the manufacture of black tea. Five major stages of production were identified, which include withering, in which fresh leaves are converted to withered leaves, followed by rolling in which withered leaves are converted to rolled leaves, followed by fermentation, in which rolled leaves yield fermented leaves, followed by drying in a drying house, which yields crude black tea from fermented leaves, and finally, drying with smoke firing, which yields the final product, i.e. black tea. All these six types of tea at various stages of manufacturing possess were examined to determine the PAH levels. The PAH concentration of crude black tea and black tea was found to be higher than the PAH levels of leaves at earlier stages of processing. Moreover, the PAH levels of the black tea leaves in the final stages were higher than those of pre-processed leaves. An investigation of the source of these extra PAH concentrations indicates that more PAHs are introduced into the leaves at the drying stage. Calculations suggest that about 94% and 98% of the PAH in crude black tea and black tea, respectively, are introduced in the drying stage. The source of these excess PAHs was found to be pine firewood, which when combusted during the drying stage, released these PAHs into the surroundings. These were then absorbed by the tea leaves. Thus, it is concluded that PAHs, which are carcinogenic, are introduced during the drying stage of manufacturing of black tea. Other possible carcinogens in tea and their possible sources will also have to be investigated. VI. Determination of Tea Polyphenols and Caffeine in Tea Flowers (Camellia sinensis) and Their Hydroxyl Radical Scavenging and Nitric Oxide Suppressing Effects (Lin, Wu and Lin 975?980) The levels of polyphenols and caffeine in tea flowers were evaluated in this study, and an examination of their anti-oxidant and nitric oxide suppressing effects was also performed. The study reveals that the polyphenols and caffeine in tea flowers are qualitatively similar to those of tea leaves. However, the levels of caffeine are lower in tea flowers compared to tea leaves. Among catechins, epigallocatechin 3-gallate is less and epicatechin 3-gallate is more in tea flowers compared to tea leaves. Tea flower extracts were found to inhibit hydroxyl-radical associated oxidative damage in cells. This activity is stronger than the anti-oxidant activity of Vitamin E and even tea leaves that were extracted in 75% ethanol. However, the anti-oxidant activity of tea flower extracts was found to be lower than that of tea leaves extracted in water. Tea flowers also contain certain nitric oxide inhibitory substances, which are comparable to those found in green and black tea. In contrast to tea leaves, extracts of tea flowers lack apoptotic effects. Other constituents of tea flowers that possess anti-oxidant and nitric oxide suppressing properties will have to be investigated in future studies. VII. Tea Catechin Supplementation Increases Antioxidant Capacity and Prevents Phospholipid Hydroperoxidation in Plasma of Humans (Nakagawa et al 3967?3973) This study sought to investigate the effects of the consumption of catechin-rich green tea on the anti-oxidant potential of human plasma. The levels of catechin in plasma after consumption of green tea extracts were similar to those in the actual extracts before consumption. About 267 pmol epigallocatechin-3-gallate was found per 1 ml of plasma after sixty minutes of supplement administration. Ingestion of catechin did not affect plasma phospholipids, cholesterol, serum albumin and total protein levels. Increase in the epigallocatechin-3-gallate levels in plasma was negatively associated with the levels of phosphatidylcholine hydroperoxide in plasma, thereby raising plasma antioxidant capacity. The study further reveals that plasma supplemented with green tea catechins is resistant to copper ion-dependant phospholipid peroxidation. Thus, catechin supplementation is found to be associated with increased antioxidant capacity of human plasma. Future studies are required to assess the dosage of tea catechins that would be beneficial for humans, the concentration of tea catechins that should be made bio-available after consumption and the metabolic pathway involved in the antioxidant enhancing effect of catechins. VIII. Polyphenolic Chemistry of Tea and Coffee: A Century of Progress (8109–8114) This study reviewed the polyphenolic chemistry of tea and coffee as investigated by other published studies. The predominant polyphenols in tea and coffee include flavonoids, especially catechins, and phenolic acids. Different types of tea such as black tea, green tea and oolong tea have different phenolic content. Green tea polyphenols undergo epimerization and black tea polyphenols undergo oxidation during brewing. Moreover, the polyphenols in coffee are degraded by lactonization and chlorogenic acid polymerization. The catechins present in tea possess antioxidant properties owing to their ROS (reactive oxygen species) and RCS (reactive carbonyl species) scavenging properties. Studies also reveal that polyphenols in tea prevent diabetes by preventing the formation of advanced glycation end products. The B ring of catechins is involved in the anti-oxidant activity while the A ring is involved in carbonyl trapping. The electron density of the A ring carbons is directly proportional to the reactive carbonyl trapping ability. The detailed mechanisms underlying the anti-diabetic activity of tea catechins will have to be elucidated in future studies. Works Cited Chen, Z et al. “Degradation of green tea catechins in tea drinks.” Journal of Agricultural and Food Chemistry 49.1 (2001): 477-482. Fukushima, Yoichi et al. “Coffee and green tea as a large source of antioxidant polyphenols in the Japanese population.” Journal of Agricultural and Food Chemistry 57.4 (2009): 1253-1259. Hertog, Michael G L, Peter C H Hollman, and Betty Van De Putte. “Content of potentially anticarcinogenic flavonoids of tea infusions, wines, and fruit juices.”Journal of Agricultural and Food Chemistry 41.8 (1993): 1242-1246. Kyle, Janet A M et al. “Effects of infusion time and addition of milk on content and absorption of polyphenols from black tea.” Journal of Agricultural and Food Chemistry 55.12 (2007) : 4889-4894. Lin, Daohui, and Lizhong Zhu. “Polycyclic aromatic hydrocarbons: pollution and source analysis of a black tea.” Journal of Agricultural and Food Chemistry52.26 (2004) : 8268-8271. Lin, YS, S S Wu, and JK Lin. “Determination of tea polyphenols and caffeine in tea flowers (Camellia sinensis) and their hydroxyl radical scavenging and nitric oxide suppressing effects.” Journal of Agricultural and Food Chemistry 51.4 (2003): 975-980. Nakagawa, K et al. “Tea catechin supplementation increases antioxidant capacity and prevents phospholipid hydroperoxidation in plasma of humans.”Journal of Agricultural and Food Chemistry 47.10 (1999): 3967-3973. Wang, Yu, and Chi-Tang Ho. “Polyphenolic chemistry of tea and coffee: a century of progress.” Journal of Agricultural and Food Chemistry 57.18 (2009): 8109-8114. Read More