http://pubs.acs.org/cgi-bin/abstract.cgi/jafcau/2002/50/i03/abs/jf010153l.html Total Phenol, Catechin, and Caffeine Contents of Teas Commonly Consumed in the United Kingdom http://pubs.acs.org/isubscribe/journals/jafcau/50/i03/figures/jf010153lf00001.html http://pubs.acs.org/isubscribe/journals/jafcau/50/i03/figures/jf010153lf00002.html http://pubs.acs.org/isubscribe/journals/jafcau/50/i03/figures/jf010153lf00003.html I'll include only some parts Materials and Methods Tea Samples. Commonly consumed teas, including green, oolong, black, and fruit teas, were purchased from supermarkets or specialized tea outlets in the United Kingdom. The Tea Council (1) reports U.K. tea imports to originate primarily from India and Kenya and contribute to an apparent consumption of 148000 tonnes (an average figure based on the past three years). Two-thirds of the U.K. population above 10 years of age (~37 million people) are reported to drink tea daily, on average three cups, and 90% of such tea is prepared from tea bags. Because tea consumed in the United Kingdom has been imported from various countries, it is probable that its composition will vary according to variety, leaf composition, and age, agronomic factors, processing conditions, and storage (during transport, retailing, and within the home) as well as degree of fermentation. Table 之後上 Results Total Phenolics. The level of total phenolics in selected black teas varied between 80.5 and 134.9 mg/g and was significantly lower (65.8-106.2 mg/g) in green tea (Table 1). Ceylon black tea contained the highest content, whereas Japanese green tea contained the lowest. Hoff and Singleton (12) have also reported similar levels of total phenolics in both black (67.7 mg/g) and green teas (62.3 mg/g). On the other hand, Manzocco et al. (13) found green tea to contain higher total phenols (95.4 mg/g) than black tea (80.1 mg/g). The present results confirm that the level of total phenols in different teas is very variable and that comparison of data from different studies on different teas (especially on unnamed brands or extracted/fractionated tea products) may be insufficient to conclude that a certain type of tea is, in general, rich or poor in total phenols. A comparison of total phenols and catechins among different green teas analyzed in this study showed most of the phenolics determined by Folin-Ciocalteu reagent to be catechins (Table 1). Catechins and Caffeine. A mixture of five catechins (EGC, C, EC, EGCG, and ECG) and caffeine from commercial products (green, oolong, black, fruit, and instant teas) purchased in the United Kingdom was separated by gradient RP-HPLC, as described above.The HPLC separation was achieved in 23 min, with a total run time of 35 min, as described by Khokhar et al. (10). The results showed that the levels of major catechins were lower in most black teas, with the exception of Darjeeling and Ceylon teas (Table 2). This could be due to varying amounts of oxidation during fermentation (likely to be an underfermentation) and handling. All of the commonly consumed commercial black teas reported in this study are classified as fully fermented teas. Catechin levels in these teas varied between 5.6 and 47.5 mg/g. Ceylon tea contained the highest amounts followed by Darjeeling and Twinings, with Lapsang the lowest; all showed an overall similar trend among individual catechins (EGCG > ECG > EC > EGC > C). The catechin compositions of Ceylon (high in catechins) and PG Tips (low in catechins) teas purchased in the United Kingdom in 1996 (10), and in the present study, were similar; their lower catechin contents may thus reflect the composition of the plant and the manufacturing process. The amounts of caffeine were similar (25-28 mg /g) for all black teas, except Darjeeling (22 mg/g), a difference that may reflect variation in the degree of fermentation. It is likely that the highest quality teas (that is, the more expensive specialized brands, Darjeeling and Ceylon), are produced according to more strictly controlled fermentation and drying processes than is the case for teas of lower quality, which possess stronger color due to increased catechin oxidation. Fernández et al. (14) reported the caffeine content of black teas from a variety of origins to range between 25.7 and 34.2 mg/g, whereas two samples of instant tea analyzed for 36.9 and 38.3 mg of caffeine/g. So-called "decaffeinated" tea contained much reduced levels (2.7 mg/g) of caffeine rather than a complete absence of this compound. The levels of catechins in the green teas varied from 51.5 to 84.3 mg/g (Table 2). EGCG was the major constituent of the Chinese and Indian teas, and the trends of their individual catechin contents (EGCG > EGC > ECG > EC > C) were similar. In contrast, the Japanese teas (except Osaka-Fu, a tea product) contained higher levels of EGC and EC and an overall trend of EGC > EGCG > EC > ECG > C. Lin et al. (14) have also reported higher levels of EGC and EC in Japanese green teas and higher levels of ECG in Chinese green tea. The caffeine content of green teas varied between 11 and 20 mg/g and was found to be higher in the Indian and Chinese teas as compared to those from Japan; these contents are lower than most reported by Fernández et al. (14), which range from 7.74 to 34.1 mg/g. Lin et al. (15) reported that levels of caffeine were significantly elevated in fermented teas, which may suggest a very mild fermentation in green teas from India and China. Generally, fermentation has little effect on caffeine levels in the leaf; the variation could, therefore, be due to the variety of tea and the structure of the leaf that can influence the kinetics of the infusion process. The fruit-flavored teas examined all possessed similar contents of catechins (8.5-13.9 mg/g) and caffeine (24-25 mg/g). This might be expected as all were of the same brand (Pickwick) and presumably reflects the addition of different flavors to a common tea base. Effect of Temperature on Catechins and Caffeine Extraction. This was studied by extracting the teas at 100, 80, or 60 C for 5 min (Figure 1). The levels of total phenols, individual catechins, and caffeine increased with extraction temperature and were greatest for teas that were aqueous extracted at 100 C for 5 min. Catechin contents increased by 30-40% when teas were extracted for an extended period of 10 min (typically, domestic tea infusions are prepared in much less than 5 min). The compounds most sensitive to extraction conditions were EGCG and ECG. Chen et al. (16) have studied the effects of extraction temperature and time on the polyphenol content of oolong tea and found an increase in catechin content with increasing extraction temperature; these authors suggested that the total polyphenol levels were highest when extracted at 77-80 C. --

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