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ABSTRACT

This paper focuses on the effects of three thermal drying methods (microwave-, oven- and sun-drying) and one nonthermal drying method (freeze-drying) on the AOP of leaves of Vitex negundo and Vitex trifolia, which are consumed traditionally as herbal tea. Microwave-drying and freeze-drying were found to be able to maintain the AOP of the leaves but oven-drying and sun-drying resulted in deterioration of AOP. Microwave-drying has the advantage of short drying time and low water activity. AOP of Vitex herbal tea leaves that are microwave-dried and freeze-dried were not affected by storage up to 30 days.

PRACTICAL APPLICATIONS

Tea, one of the most widely consumed beverages apart from water, has long been known for its health-promoting benefits in terms of its antioxidant properties due to its high phenolic content. Much of such studies, however, focus on green tea (Camellia sinensis). Although V. negundo and V. trifolia have been consumed traditionally as herbal tea, understanding of its antioxidant properties remains scarce. Drying serves as a vital part of tea processing, affecting its antioxidant content and appearance which in turn affects the commercial value of the tea. This study therefore serves as an important work in providing insights into the antioxidant properties of Vitex species and the best drying method of its leaves as herbal tea for commercial purpose. In addition, this study also provides insights into the effect of different drying methods on the storage of the leaves which is of value to the tea processing industry.