Improving the stability and bioavailability of tea polyphenols by encapsulations: a review

Tea polyphenols (TPPs) have attracted significant research interest due to their health benefits. However, TPPs are sensitive to certain environmental and gastrointestinal conditions and their oral bioavailability was found to be very low. Delivery systems made of food-grade materials have been reported to improve the shelf-life, bioavailability and bioefficacy of TPPs. This review discusses the chemistry of TPPs; the setbacks of TPPs for application; and the strategies to counteract application limitations by rationally designing delivery systems. An overview of different formulations used to encapsulate TPPs is provided in this study, such as emulsion-based systems (liposome, nanoemulsion, double emulsion, and Pickering emulsion) and nano/microparticles-based systems (protein-based, carbohydrate-based, and bi-polymer based). In addition, the stability, bioavailability and bioactivities of encapsulated TPPs are evaluated by various in vitro and in vivo models. The current findings provide scientific insights in encapsulation approaches for the delivery of TPPs, which can be of great value to TPPs-fortified food products. Further explorations are needed for the encapsulated TPPs in terms of their applications in the real food industry as well as their biological fate and functional pathways in vivo.