Changes in Polyphenols of the Seed Coat during the After-Darkening Process in Pinto Beans (Phaseolus vulgarisL.)

Abstract

Proanthocyanidins and flavonoids were isolated and identified from seed coats of two aged and nonaged pinto bean lines: 1533-15 and CDC Pintium. The seed coat of 1533-15 darkens slowly and never darkens to the same extent as CDC Pintium. Analysis of the overall level of proanthocyanidins using a vanillin assay demonstrated that aged and nonaged seed coats of CDC Pintium had significantly higher levels of proanthocyanidins than aged and nonaged 1533-15 seed coats. Aged and nonaged seed coats of both lines were found to contain one main flavonol monomer, kaempferol, and three minor flavonols, kaempferol 3-O-glucoside, kaempferol 3-O-glucosylxylose, and kaempferol 3-O-acetylglucoside. These compounds were identified by NMR and ESI-MS analysis (except for kaempferol 3-O-acetylglucoside, which was tentatively identified only by ESI-MS analysis) and quantified using HPLC-DAD. The combined concentrations of all the kaempferol compounds in seed coats of CDC Pintium were significantly higher than in seed coats of 1533-15, and the combined contents did not change after aging. The content of kaempferol decreased nearly by half in the seed coats of CDC Pintium after aging, whereas no significant change was observed in the seed coats of 1533-15. Proanthocyanidin fractions from both lines, aged and nonaged, were subjected to LC-MS/MS analysis and found to be composed primarily of procyanidins. Procyanidins in the seed coats were predominantly polymers with the degree of polymers higher than 10. The proportion of these polymers decreased after aging, while that of the low-molecular-weight procyanidins increased. A catechin-kaempferol adduct was tentatively identified in both lines by LC-MS/MS, and the concentration increased in the seed coats after aging.

Common bean genotypes for agronomic and market-related traits in VCU trials

“…Darkening in beans may be related to the presence of polyphenolic compounds (Beninger et al, 2005), and these compounds are directly connected with plant defense against pathogens (Islam et al, 2003). Selection directed to obtaining lighter-colored grains causes the phenolic compounds to be reduced in the plant, for these compounds are active in oxidation which accelerates grain darkening.…”

Influence of Storage on Darkening and Hardening of Slow- and Regular-Darkening Carioca Bean (Phaseolus vulgaris L.) Genotypes

“…Seed coat darkening and increased cooking time are associated with the "hard-to-cook" (HTC) phenomenon found in some legume species, particularly dry bean. The exact causes of postharvest darkening are not well-known, but include a combination of environment, genetics, and chemical changes that take place within the seed coat (Beninger et al, 2005). Darkening is accelerated by exposure to light, high temperature, and humidity prevalent during postharvest carioca bean storage in Brazil.…”

Physicochemical, morphological and rheological properties of canned bean pastes “negro Queretaro” variety (Phaseolus vulgaris L.)

“…The post harvest storage of beans at different conditions of temperature, time and humidity may cause hard-to-cook phenomenon, starch gelatinization, loss of nutrients, change in polyphenols of the seed coat, and decrease of the antioxidant activity (Beninger et al 2005;Machado et al 2008). Several authors have reported that the processing condition of beans modifies their nutritional and textural properties.…”