Antioxidant activity of common beans (Phaseolus vulgaris L.)

Four bean varieties with different hull colors (white, red, brown and black) were extracted with 80% acetone and evaluated for their total, hydrophobic and hydrophilic phenolics as well as tannin contents. The tannin content was measured using three different methods. Antioxidant capacity of the extracts was assessed using beta-carotene/linoleate and bulk corn oil model systems. The content of hydrophobic antioxidants was higher compared with the hydrophilic fraction in all tested bean types. Evaluation of antioxidant activity in a P-carotene model system revealed that red, brown and black whole bean extracts were capable of inhibiting oxidation (33-52%) of beta-carotene as compared with the control when used at 100 p.p.m. level as catechin equivalents. In the corn oil model system, red, brown and black bean extracts inhibited the formation of conjugated dienes (CD; 20-28%), thiobarbituric acid reactive substances (TBARS; 44-52%) and hexanal (68-84%) when used at 100 p.p.m. level as catechin equivalents. The results of this study demonstrated that colored beans possess superior antioxidative activity compared with white beans.