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Folacin content of tea
The purpose of this study was to investigate the folacin activity of five types and 14 brands of tea using the current microbiological assay method with Lactobacillus casei employed as the test organism and ascorbate added as antioxidant. Substantially higher amounts of folacin were found in teas than that reported previously in the literature. Green tea leaves possessed the highest total folic acid (TFA) content, ranging from 9.48 mcg/g to 12.75 mcg/g and with an average of 11.20 mcg/g. Black tea leaves had highest free folic acid (FFA) content, ranging from 1.36 mcg/g to 2.07 mcg/g with an average of 1.74 mcg/g. Oolong tea leaves had a low folacin content when compared to green and black tea leaves with an average of 0.38 mcg/g in FFA content and 3.53 mcg/g of TFA. Herb tea did not show much folacin activity. The reason for this decrease of activity is due to the insignificant amount of folacin in the major raw materials used to manufacture herb teas. Different brands of instant tea contained various amounts of folacin. In one gram of instant tea powder, pure instant teas (100%) had the highest folacin content while instant tea mix (sugar and lemon flavored) showed the lowest folacin activity. When comparing with hot water prepared instant teas, the cold water prepared instant teas had higher FFA content and lower TFA content. This may suggest that the FFA of instant tea is more labile to heat than TFA while TFA has higher solubility in hot water than in cold water. The amount of folacin extracted from tea leaves into tea brews during 5 minutes hot water infusion differs among folacin types and tea types. The average percentage of folacin extracted from tea leaves were 62% of both FFA and TFA from green tea, 51% FFA and 70% TFA from black tea, and 38% FFA and 62% TFA from oolong tea. The tea bag itself was found to have inhibitory effects on the extraction of folacin from tea leaves into tea infusions. The average percentages of FFA and TFA extracted from tea leaves were 52% and 64%, when brewed with tea bags, and 77% and 76% when brewed without tea bags. When comparing folacin content of other foods and beverages, tea leaves and tea brews can be regarded as a good source of folacin. Therefore, tea should be considered when evaluating folacin intake and could serve as a better alternate than some other common beverages by providing more folacin in the daily diet.