Optimization of microwave assisted extraction and biological activities of total flavonoids from grape seed using response surface methodology

Aiming to reduce the environmental contamination and resource wastage generated by discarded grape seed, the management of discarded grape seed should be carried out and their potential bioactivities and pharmacological properties ought to be exploited to the fullest extent possible. A Box–Behnken design of response surface methodology was employed to further optimize microwave-assisted extraction setting for grape seed total flavonoids (GSFE). In addition, the extract (GSFE) of total flavonoids obtained were refined through AB-8 macroporous resin for obtaining more pure flavonoid (GSFP) with determination of their in vitro hypoglycemic activity and antioxidant activity. The results indicated that following optimized extraction conditions were achieved: ethanol concentration 50% liquid-solid ratio 21:1 mL/g, microwave power 540 W, microwave time 126 s. Below mentioned conditions, the extraction yield reached an average experimental value (1.979 mg/g), representing 1.69 times higher than that of water extraction (1.17 mg/g). In contrast to GSFE, the purity of GSFE after purification (GSFP) exhibited a high degree of purity at 13.753 mg/g, representing nearly 2.50 times that of GSFE (3.926 mg/g). GSFP possessed high α-glucosidase and α-amylase inhibitory activities as well as DPPH and ABTS + free radical scavenging activities with an IC50 value of 0.00641, 0.0257, 0.0669 and 0.0708 mg/mL, inferior to that of GSFE (0.0514, 0.186, 0.129 and 0.223 mg/g). Within present work, the microwave technique for extraction of total flavonoids from grape seeds was investigated with an efficient and cost-effective extraction method. Total flavonoids of grape seeds have certain in vitro blood glucose and antioxidant activity, and the purified total flavonoid biological activity has improved, laying the foundation for further study of its pharmacological activity.