Faster cooking times and improved iron bioavailability are associated with the down regulation of procyanidin synthesis in slow-darkening pinto beans (Phaseolus vulgaris L.)

Abstract

Seed coat darkening after a delayed harvest or prolonged storage reduces the commercial value of dry beans and is caused by the oxidation of procyanidin compounds (condensed tannins). Slow-darkening (SD) pinto beans have a recessive gene (Psd), which alters procyanidin production – postponing their darkening over time. Procyanidins are important for the processing and nutrient bioavailability of beans, therefore, this study compared the postharvest cooking times and iron bioavailability of SD pinto varieties to regular-darkening (RD) pinto varieties. The results show SD pinto beans cook 30% faster and provide 2–7 times more bioavailable iron than RD pinto beans. No relationship between iron bioavailability, iron and phytate concentrations were detected among the pinto beans. However, lower procyanidin concentrations were strongly associated with faster cooking times and improved iron bioavailability of SD pinto beans. These findings indicate that the SD trait benefits the cooking quality and iron bioavailability of stored beans.

Keywords

• Phaseolus vulgaris L.
• Slow-darkening
• Iron bioavailability
• Phytate
• Procyanidins
• Kaempferol 3-glucoside