Phytotherapy with active tea constituents: a review

Tea is a widely renowned functional beverage originating from processed tender leaves of the Camellia sinensis plant after brewing with hot water. This refreshing and revitalizing beverage has been recognized as an essential commodity since ancient times. Tea constituents have many health benefits and hence find usage in functional foods, beverages, and nutraceuticals. Nonetheless, the clinical usage of tea constituents is limited by the high molecular weight, poor stability, and low bioavailability of some active components. We review how fresh tea leaves are processed into different forms of tea such as green, oolong, white, and black teas. The major tea constituents, e.g., catechins, caffeine, and theanine, exhibit numerous health properties such as antioxidant, anti-inflammatory, anticancer, antidiabetic, cardioprotective, and antimicrobial. We discuss methods to enhance the efficacy and applicability of active tea constituents, such as micro- and nanoencapsulation techniques.