Antinutritional factors and antioxidant activity in improved varieties of common bean (Phaseolus vulgaris)

Common bean is important in the Mexican diet. It supplies 20 to 40% of protein, B complex vitamins and minerals such as iron and calcium. Bean starch is a supply of energy and structural carbon for further metabolic synthesis. However, the presence of antinutritional factors in beans such as trypsin inhibitors, phytic acid, oligosaccharides and tannins reduces their biological value. The objective of this study was to characterize antinutritional factors as well as to determine the biochemical factors of improved bean seed coats as an alternative source of antioxidant compounds, other than just fiber, in a group of 16 common bean improved cultivars. Bean seeds with higher percentage of seed coat were those of black and beige colored cultivars, which had medium (25 to 38 g 100 seeds(-1)) to large (>40 g 100 seeds(-1)) seed size, respectively. Bean cultivars had 3.83 to 5.60% oligosaccharide cotyledon content, with no statistical differences (p>0.05) among them. Phytic acid percentage ranged from 0.10 to 0.22% with Mayacoba cultivar showing the highest content (2.16 +/- 0.03 m g(-1)). The trypsin units inhibited (UTI mg(-1)) by bean flour extracts varied from 4.78 to 12.22 UTI mg(-1); the highest value was found in Flor de Mayo M38 cultivars. The bean cultivars with higher antioxidant capacity were associated to seed coat color.