Submitted to: Journal of American Society of Horticulture Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/20/1999
Publication Date: N/A
Citation: Interpretive Summary: Flavonoids are chemicals that impart the various colors to seed coats of common bean (Phaseolus vulgaris L.). Flavonoids and tannin compounds which are flavonoid polymers hooked together in chains may form indigestible complexes with proteins and carbohydrates in the seed thus causing flatulence and reducing the nutritional value of beans to consumers. We conducted an experiment to identify flavonoids in three genetic stocks of dry bean for which the seed coat color genotypes are well-known. Only one flavonoid compound called astragalin was found in mineral brown, yellow-brown, and pale greenish brown-the three genotypes studied. Tannins were also found in the three genotypes, but were not identified as to their chemical makeup. Astragalin is not known to complex with proteins or carbohydrates in beans but tannins are. If the genes for particular tannin polymers can be discovered, plant breeders can eliminate them through selective breeding. The removal of tannins from beans may lead to improved health and well-being of consumers.
Technical Abstract: Flavonoid chemicals were isolated and identified from three dry beans (Phaseolus Vulgaris L.) differing in seed coat color genotype. Kaempferol-3-O-B-D-glucoside (astragalin) was isolated and identified with NMR spectroscopy from mineral brown (genotype; P,C,D,J,G,B,v), yellow-brown (genotype; P,C,J,G,b,v) and pale greenish brown (genotype; P,C,D,J,g,b,v) and was the main flavonoid monomer present. High pressure liquid chromatography analysis indicated that astragalin was present at similar concentrations for pale greenish brown and mineral brown, but was significantly lower for yellow-brown. We could not determine the function of the G or B genes, but the presence of astragalin in the three genotypes indicates that these genes do not appear to act in a qualitative manner with regard to astragalin production. It is also not clear whether B and G control the amount atragalin present. No anthocyanins were detected in any of the genotypes. Flavonoid polymers (condensed tannins) were detected in the genotypes by thin layer chromatography. The differences in color among mineral brown, yellow- brown, and pale greenish brown may be due to the type and amount of tannins present. Another plausible explanation for the differences in the brown hues among the genotypes may be due to non-flavonoid pigments not under control of known seed coat color genes.