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Green tea (Camellia sinensis L.) is a known source of antioxidants. It is rich in gallic acid, catechins, caffeine and other phenols. There is a lot of current research on tea antioxidants in different types of tea, their origin and growing environment, and processing conditions. Recent research by Friedman et al (2009) studied tea antioxidants’ potential decline over time during storage.

Friedman et al (2009) bought 8 different teas from US supermarkets. The authors did not know history of the teas (e.g. age, growing area, storage & processing conditions). Six of the teas were US brands, two were Japanese, and there was one Korean brand. After purchase, the teas were stored for 1 week, and 1, 2, 4 or 6 months in the dark at room temperature. The authors analyzed the tea samples by HPLC and collected data on catechins: e.g. epicatechin (EC), epicatecin-3-gallate (ECG),epigallocatechin (EGC) and epigallocatechin-3-O-gallate (EGCG) among others.

At the beginning of the experiment (e.g. 0 days storage) Friedman et al (2009) found quit a bit of variation in total catechins among the 8 different teas. There was a range in total catechins from 23.06 mg/g to 169.95 mg/g. EGCG, believed to be the most potent antioxidant, varied from 13.33 to 113.04 mg/g among the 8 teas at 0 days of storage. Thus there is a lot of variation in catechins in store bought green teas (Freedman et al., 2009).

The amount of total catechins declined over time in the stored tea. For example, the total catechins for the highest yielding tea at 0 days storage, declined from 169.95 mg/g to 100.25 mg/g after 4 months of storage. The EGCG in this tea brand declined from 113..04 mg/g to 71.08 mg/g during 4 months of storage. The total catechins for the lowest yielding tea at 0 days storage declined from 23.06 mg/g to 4.72 mg/g after 4 months of storage. The EGCG in the lowest yielding tea brand declined from 13.33 mg/g to 5.57 mg/g after 4 months of storage. The authors report an average overall loss of 32.5% in total catechins content at the end of 6 months of storage (Freedman et al., 2009). Friedman et al. (2009) conclude that even in the absence of moisture the quality of tea may decline over time.

Reference:

Friedman, M. C.E. Levin, S.-U. Lee, and N. Kozukue. 2009. Stability of green tea catechins in commercial tea leaves during storage of 6 months. J. Food Sci. 74:H47-H51.

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