Effects of ultrasound-assisted bath, probe, and extraction time on bioactive compounds and antioxidant activity in white tea (Camellia sinensis) extracts from purple- and green-leaf cultivars

Abstract This study investigates the effects of ultrasonic-assisted extraction (UAE) methods, specifically bath (35 kHz, 320 W) and probe (250 kHz, 750 W), along with varying extraction times (5, 10, and 15 min), on the bioactive compounds and antioxidant activities of white tea ( Camellia sinensis) extracts from two purple-leaf cultivars (SS-2 and SS-3) and one green-leaf cultivar (GMB-7). High performance liquid chromatography (HPLC) was employed to quantify catechin, epicatechin, epigallocatechin gallate (EGCG), gallic acid, and caffeine. Additional analyzes included total phenolic content (TPC), total flavonoid content (TFC), monomeric anthocyanins, and antioxidant activity (DPPH and FRAP assays). Results showed that UAE probe extraction yielded higher concentrations of bioactive compounds, while the UAE bath preserved greater antioxidant activity. TPC ranged from 318.52 to 352.51 mg GAE/g for the bath method and 327.53 to 376.45 mg GAE/g for the probe. Longer extraction times improved both phytochemical content and antioxidant capacity across all cultivars. Purple-leaf cultivars exhibited significantly higher levels of anthocyanins, polyphenols, and flavonoids ( p < 0.05 ), whereas the green-leaf cultivar demonstrated a higher carotenoid content. Multivariate analyzes, including principal component analysis (PCA) and heat map visualization, revealed different clustering patterns based on cultivar type and extraction method, explaining 70.82% of total variance. These findings highlight the effectiveness of UAE techniques in producing bioactive-rich white tea extracts, particularly from purple-leaf cultivars, with potential applications in functional foods, nutraceuticals, and cosmetics.