Evaluation of the antioxidant activity of extracts and flavonol glycosides isolated from the seed coats of coloured beans (Phaseolus vulgaris L.)
The seed coat of the common bean (Phaseolus vulgaris L.) can be considered an important source of flavonoids. Flavonoids are well known for their beneficial effects on health long before they were isolated as effective compounds. Dry beans are typically processed and the seed coats may be removed and discarded prior to consumption. Therefore, a better understanding of the antioxidant and anti-inflammatory activity of coloured dry bean seed coats would be beneficial in determining their potential use as an ingredient in the functional food and nutraceutical industry. Flavonol glycosides were identified from acetone extracts of seed coats of black beans, pinto beans, and dark and light red kidney beans, representing nine varieties grown in Manitoba. Based on HPLC-MS/MS, black beans contained the 3-O-glycosides of kaempferol, quercetin, and myricetin. Pinto beans contained kaempferol 3-O-glycosides, while light and dark red kidney beans contained quercetin 3-O-glycosides. In addition, we reported the presence of a flavonol triglycoside for the first time in dry bean seed coats. Concentrations of kaempferol-3-O-glucoside were the greatest varying from 0.44 to 7.08 to mg/g of dried seed coat weight, followed by quercetin-3-O-glucoside varying from 0.91 to 3.84 mg/g of dried seed coat weight, and then rutin varying from 0.13 to 0.22 mg/g of dried seed coat weight. The DPPH method demonstrated seed coat crude extracts of Eclipse, a black bean, and Windbreaker, a pinto bean, to have the highest antioxidant activities among the samples. Eclipse, with the maximum concentration of total phenolic compounds, exhibited an antioxidant activity of 57,816 μmol trolox equivalent/100g of dried seed coat weight and Windbreaker, with the maximum concentration of total flavonoid compounds, exhibited an antioxidant activity of 57,451 μmol trolox equivalent/100g of dried seed coat weight. Cellular measures of anti-inflammatory activity of seed coat crude extracts in LPS-induced murine macrophage RAW 264.7 cells showed both anti- and pro-inflammatory effects. Extracts of Windbreaker and Eclipse decreased TNF-α levels, suggesting anti-inflammatory properties, while other varieties showed increased levels of TNF-α production, or pro-inflammatory activity. The results indicate seed coats of Windbreaker and Eclipse may have the potential to be used as a functional food ingredient and possibly prevent disease and enhance human health.