GPE (µg/ml) GA (µM) SA (µM) Protective effects of pre-treatment with a grape by-products phenolic extract (GPE), gallic acid (GA) or syringic acid (SA) to exposure of pro-oxidant t-BOOH Non-enzymatic defences: Glutathione reductase (GSH) Enzymatic defences: Glutathione peroxidase (GPX) GPx (mU/mg protein) GSH (ng/mg protein)

Zhang and Wang: Total Polyphenols from Vigna angularis and their EffectsVigna angularis, also called adzuki bean, a member of the family Fabaceae, has long been cultivated in Asian countries. This legume has received considerable attention owing to the presence of polyphenols. The optimal extraction conditions for total polyphenols from V. angularis and their antioxidant activities were investigated in this study. Ultrasound-assisted extraction was used to optimize the extraction of total polyphenols from V. angularis. Factors that influenced the extraction efficiency, such as ethanol concentration, liquid-solid ratio, and ultrasonic time were investigated by Box-Behnken design. Folin-Ciocalteu colorimetry was adopted to determine the total polyphenol content by using gallic acid as a reference. Antioxidant activities of the total polyphenols were evaluated by 1,1-diphenyl-2-picrylhydrazyl, hydroxyl and superoxide radical-scavenging activity assays. The optimized extraction conditions were as follows: ethanol concentration of 44.3%; liquidsolid ratio of 21.6:1 and ultrasonic extraction time of 30 min. Under these optimal conditions, the model's predicted extraction efficiency was 4.19 mg/g. The mathematical model had a high correlation (P<0.05) and could be employed to extract total polyphenols from V. angularis. In vitro antioxidant activity results showed that total polyphenols had strong antioxidant capacity and could be used as potential antioxidant agents. This study provided a reference for the exploration of new natural antioxidants. Key words: Vigna angularis (Adzuki bean), total polyphenols, extraction, Box-Behnken design, response surface methodology, antioxidant activityThe extraction of phytochemicals from food plants using solvents is an important step in separation and bioactivity research. Thus, efficient extraction techniques are required to harvest the natural products. Ultrasound-assisted extraction (UAE) is an efficient extraction technique that can help solutes more rapidly diffuse from the solid material into the solvent [1] . UAE has been widely used owing to its high efficiency, shorter processing time and reduced solvent consumption.Vigna angularis, also called adzuki beans, a member of the family Fabaceae, is an important food crop and used as folk medicines in Asian countries [2] . V. angularis have relatively small beans (about 5 mm). Most of the adzuki beans cultivated in Eastern Asian countries are red in color. This legume is rich in dietary fibers, proteins, minerals, vitamin A, vitamin B9 and folate [3] . Due to its biochemical components, V. angularis has been evaluated as a new treatment option. In addition, it has received considerable attention owing to the presence of polyphenols, such as proanthocyanidins and quercetin [4] . Numerous studies have demonstrated that polyphenols possess antioxidant [5,6] , anticarcinogenic [7,8] , antiglycation [9] and neuroprotective [10] properties. However, there are no data relating to optimized extraction conditions of total polyphenols (T...