Effect of Storage Temperature and Water Activity on Antioxidant Activities of Powdered Green Tea Extracts

The antioxidant properties of green tea leaves and powder extracts were determined using several tests including estimation of reducing power, DPPH(1,1-diphenyl-2- picrylhydrazyl) radical-scavenging activity, and FRAP(Ferric reducing/antioxidant power) assay. All tests indicated that extracts of green tea powder had higher antioxidant activities than extracts of green tea leaves, and the activities were concentration-dependent. However, each test yielded somewhat different results with respect to storage conditions. The reducing power of green tea leaves was highest at , storage at , and an Aw(water activity) value of 0.23. However, the reducing power of green tea powder, assayed at , was high under all storage conditions(with variations in temperature and Aw), and was about 1.5.2-fold greater than that of green tea leaves. Radical-scavenging activity, as assessed by the DPPH assay, increased in a dose-dependent manner over the range . At higher concentrations, activities were of maximal were attained. The FRAP activity of green tea extract also increased with rising concentration. Particularly in the case of green tea leaves, antioxidant activity was most greatest with storage at and Aw values of 0.69 and 0.23 when assayed at a concentration of . These results indicate that the most important factor during storage of green tea is not the Aw value but rather temperature, and that use of refrigeration() is preferable to increase or maintain the antioxidant activities of biological components in green tea.