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

Authors: Wiesinger, Jason; OSORNO, JUAN - North Dakota State University; MCCLEAN, PHILLIP - North Dakota State University; HART, JONATHAN - Former ARS Employee; Glahn, Raymond

Submitted to: Journal of Functional Foods
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/7/2021
Publication Date: 4/28/2021
Citation: Wiesinger, J.A., Osorno, J.M., Mcclean, P.E., Hart, J.J., Glahn, R.P. 2021. Faster cooking times and improved iron bioavailability are associated with the down regulation of procyanidin synthesis in slow-darkening pinto beans (Phaseolus vulgaris L.). Journal of Functional Foods. 82:104444. https://doi.org/10.1016/j.jff.2021.104444.
DOI: https://doi.org/10.1016/j.jff.2021.104444

Interpretive Summary: Slow-darkening pinto beans are gaining popularity in world markets because of their preferable bright seed coat appearance after storage. This research provides evidence that the slow-darkening trait (Psd) also benefits the cooking quality and iron bioavailability of stored pinto beans. This study compared the cooking times and iron bioavailability of regular-darkening and slow-darkening pinto bean varieties six months after harvest. Slow-darkening pinto beans had significantly faster cooking times and deliver more bioavailable iron than regular-darkening pinto beans collected from different production sites in North Dakota. The results show that lower concentrations of flavan-3ols (catechins) and condensed tannins (procyanidins) were strongly associated with the faster cooking times and higher iron bioavailability of slow-darkening pinto beans. More importantly, these findings demonstrate that down regulating the synthesis of condensed tannins with the PD gene could be a novel breeding strategy to improve the cooking quality and iron bioavailability of other dry bean commercial classes that are prone to seed coat darkening, such as carioca, yellow, cranberry or red kidney.

Technical 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.