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Effect of Relative Humidity and Storage Temperature on the Quality of Green Tea Powder

After storing green tea powder for three months at three different temperatures (-20, 4, and 20 o C) with three different relative humidities (RHs) (23, 69, and 81%), the chemical quality was evaluated with green tea, which was prepared by soaking 1.5 g of the powder into 100 mL of distilled water at 70 o C for 5 min. Total phenolic contents, total flavanol contents, and ascorbic acid contents of green tea powder stored at 4 o C with 23% RH changed from 267.5, 49.4, and 24.2 mg/g to 287.1, 44.9, and 36.9 mg/g, respectively, compared to the powder before storage. EGC and EGCG, the main catechins of green tea, also changed from 16.9 and 27.3 mg/g to 24.3 and 36.5, g/g, respectively, after storage for 3 months at 4 o C with 23% RH. However, when the green tea powder was stored at -20 or 20 o C with higher RH such as 69 and 81%, the chemical compounds were significantly decreased. The results indicate that temperature and RH are important during storage of green tea powder, and low RH and refrigerated condition (-4 o C) are preferable to increase or preserve the chemical compounds of the tea.