Radio frequency-assisted enzymatic extraction of anthocyanins from Akebia trifoliata (Thunb.) Koidz. flowers: Process optimization, structure, and bioactivity determination

Anthocyanins are active compounds with various biological activities and are abundant in Akebia trifoliata (Thunb.) Koidz flowers. To extract anthocyanins from the flowers more effectively, a novel procedure of radio frequency heating-assisted enzymatic extraction was proposed in this study. The extraction conditions were optimized using Plackett-Burman and Box-Behnken design. The optimal extraction conditions were enzyme ratio of cellulase and pectinase of 1:1, enzyme concentration of 1.0 %, ethanol concentration of 50 %, liquid-solid ratio of 50 mL/g, pH of 4, and radio frequency pretreatment at 40 degrees C for 10 min with electrode gap of 5 cm. The results showed that radio frequency assisted enzyme extraction exhibited the highest crude yields (26.55 %) and anthocyanin content (50.87 mg cyanidin-3-O-glucoside equivalents/100 g) compared with hot water, acidified ethanol and enzymatic (pectinase and cellulase) assisted extractions. This method was effective for achieving high 1, 1-diphenyl-2-picrylhydrazyl radical scavenging activity (385.03 Trolox equivalents/g extract), reducing power (361.85 Trolox equivalents/g extract) and tyrosinase inhibitory (14.67 kojic acid equivalents/g extract) activity as well as significant a-amylase inhibitory activity. Nine anthocyanins were identified and did not detect any significant compound degradation using the novel approach. Accordingly, the proposed radio frequency and cellulase/pectinase combined extraction of anthocyanins was efficient and rapid. This method holds great promise for extracting bioactive compounds from plants and fruits.