Efficient enrichment of total flavonoids from kale (Brassica oleracea L. var. acephala L.) extracts by NKA-9 resin and antioxidant activities of flavonoids extract in vitro

This work established an effective method for kale flavonoids enrichment by resins. Resin screening, adsorption kinetics and isotherms, dynamic adsorption and desorption tests were conducted to optimize the appropriate resins and enrichment conditions. The results showed that NKA-9 was the optimum resin. The best adsorption conditions were 0.2 mg/mL flavonoids concentration, 12.5 bed volume (BV) sample volume and 2 BV/h adsorption rate. The desorption conditions were 3 BV of 80% ethanol at 2 BV/h elution rate. Under these conditions, the product purity was 31.16%. The purified flavonoids extract was mainly comprised of Kaempferol-3-O-sophoroside-7-O-diglucoside, Kaempferol-3,7,4'-O-d-triglucoside, Kaempferol-3-O-feruloyl-sophoroside-7-O-d-glucoside, and Kaempferol-3-O-sinapoyl-sophoroside. Moreover, it presented higher scavenging ability against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and hydroxyl (OH) radical than crude extract. In conclusion, kale flavonoids can be well concentrated by NKA-9 resin and the purified flavonoids extract has good antioxidant activity which can be potentially applied in food, cosmetic or pharmacy industries.