Functional-by-design: microencapsulated purple tea (Camellia sinensis var. assamica cv. Zijuan) polyphenols as an antioxidant ingredient in milky tea

Tea is a widely consumed and trendy beverage worldwide. All tea is derived from the leaves of the Camellia sinensis, which belongs to the Theaceae family. Throughout the years, various teas have displayed health benefits after human consumption, with green tea, in particular, attracting popularity. However, purple tea (Camellia sinensis var. assamica cv. Zijuan), which has yet to be investigated, has become of recent interest due to the many bioactivities it has displayed, including antioxidant and anti-inflammatory attributed to the phenolic compounds, especially flavanols. The use of purple tea in food models has not yet been completed hence the aims of this study were to optimise the extraction of phenolic compounds by ultrasound-assisted extraction (UAE), assess the antioxidant effects and composition of the purple tea extract (OPM), and determine its antioxidant capacity potential in milky teas containing microencapsulated OPM. OPM had a total phenolic content (TPC) of 331 mg/g, where (-)-epigallocatechin gallate was the main compound (50 mg/g). OPM showed antioxidant capacity using different test tube-based assays, decreased reactive oxygen species (ROS) generation and formation of thiobarbituric acid reactive substances (TBARS) in human erythrocytes, and decreased the formation of oxidised products (i.e., dienes) in human plasma. Additionally, OPM was able to significantly inhibit α-glucosidase (IC50 = 23.0 μg/mL) and α-amylase (IC50 = 12.4 μg/mL), and did not show significant inhibition (e.g., <70% viability) of murine astrocyte’s viability at 0.01 – 0.2 mg/mL. Milky teas containing OPM had a TPC of 561 mg/L, a content 4.5-fold greater than a standard commercial milky tea. This is the first report using microencapsulation technology as a delivery system to develop potentially functional milky teas with added polyphenol-rich extract from purple tea leaves.