Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 16, 1999
Publication Date: N/A
Interpretive Summary: Dark red kidney bean is an important market class in the U.S., and a bright seed coat with an intense garnet brown color is required for commercial and in-home use. Seed coat color in beans is determined by the kinds and amounts of natural components called flavonoids. Three flavonoid compounds were identified in the seed coats of 'Montcalm' a popular dark red kidney bean variety. Two of the flavonoids are related to the compound called quercetin and a third compound is known as kaempferol. After further analysis the quercetin and kaempferol flavonoids were yellow in color and could not be responsible for 'Montcalm's' red color. An additional experiment was conducted to identify another class of flavonoids called proanthocyanidins in the kidney bean seed coat. Proanthocyanidins are complex and large molecules known as polymers. The polymerized proanthocyanidins in kidney bean seed coats are responsible for the red color and the amount of these special flavonoids determine the intensity o redness of the seed coat. Proanthocyanidins are also health chemicals because of their potent antioxidant activity in the blood of humans and other animals. Antioxidants can render cancer-causing substances in the body ineffective. The discovery of proanthocyanidins in kidney bean is important because now plant breeders can more easily breed kidney beans with the ideal red color and simultaneously increase the antioxidant potential of the bean. Kidney beans with improved color may increase the market value and profitability of the crop to farmers. Pharmaceutical companies may also benefit from our work because of the potential to extract proanthocyanidins from bean seed coats and market them as nutritionally important food supplements.
Technical Abstract: Three flavonol glycosides were isolated and identified from the commercial dark red kidney bean (Phaseolus vulgaris L.) cultivar, 'Montcalm'. In order of highest to lowest concentration these compounds were: 3',4',5,7 tetrahydroxyflavonol 3-O-Beta-D-glucopyranosyl (2 to 1)O-Beta-D- xylopyranoside (compound 1), quercetin 3-O-Beta-D-glucopyranoside (compound d2) and kaempferol 3-O-Beta-D-glucopyranoside (compound 3). Compound 1 is a flavonol glycoside that has not been reported before in P.vulgaris L. These three flavonol glycosides were yellow compounds that do not contribute to the garnet brown color of Montcalm seed coats. Red-colored compounds which tested positive for proanthocyanidins are most likely responsible for the red seed coat color of Montcalm. Previous work on the chemistry of the compounds produced from the multi-allelic seed coat gene series C-C**r-C**u indicated that neither anthocyanins nor flavonol glycosides were detected in the seed coat extracts in the presence of the c**u locus. However, the seed coat color genotype of Montcalm is c**u J g B v rk**d and three flavonol glycosides were found. Technological advances such as modern HPLC analysis of seed coat extracts may allow for detection of small amounts of compounds which previously could not be seen using paper chromatography. Alternatively, the change of the Rk allele to rk*d may allow for the synthesis of flavonol glycosides.