Proanthocyanidins from Camellia kwangsiensis with Potent Antioxidant and α-Glucosidase Inhibitory Activity

This study aimed to systematically investigate the chemical constituents and bioactivities of the traditional wild tea plant Camellia kwangsiensis Chang. An HPLC method was first established to simultaneously quantify five major components. Subsequently, extensive isolation was performed using chromatographic techniques, and the structures of isolated compounds were elucidated by spectroscopic methods. Their biological potential was evaluated through antioxidant (DPPH and ABTS⁺ radical scavenging), α-glucosidase inhibitory, and anti-inflammatory (inhibition of nitric oxide production) assays. The LC-MS/MS analyses confirmed the absence of caffeine, theophylline, and theobromine. A total of 19 phenolic compounds were first isolated and identified, including one new proanthocyanidin, namely kwangsienin A (1), and 18 known phenolic components with six proanthocyanidins (2-7), one catechin (8), six flavonol glycosides (9-14), and five simple phenols (15-19). Notably, the proanthocyanidins displayed stronger or comparable antioxidant and α-glucosidase suppressive activity than the positive controls. In conclusion, C. kwangsiensis, rich in proanthocyanidins and naturally caffeine-free, represents a promising plant resource for developing decaffeinated functional tea beverages with antioxidant and hypoglycemic potential.