Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/20/1999
Publication Date: N/A
Citation: Interpretive Summary: Dry beans are an important source of dietary protein in the United States as well as in many developing countries of the world. Recent work has shown that the digestibility of dry bean can be affected by the amount and kind of compounds found in the seedcoat. In particular, certain naturally occurring compounds called flavonoids and tannins can form indigestible complexes with seed proteins, causing intestinal gas and reduced nutritional value of the type of bean consumed. We conducted an experiment using three types of dry bean of known seed coat genotype to find out which compound(s) give bean seed coats their color. Mineral brown has the dominant seedcoat color genes, G and B while yellow-brown and pale greenish-yellow differed from mineral brown by one or more recessive gene substitutions at the G and B chromosome sites. Only one flavonoid called astragalin was found in all three genotypes. We were able to determine the effect of the G gene for seedcoat color. When the G locus is in the recessive form i.e., g, seedcoats contain much less astragalin than when in the dominant i.e., G form. Hence, G probably controls the amount of astragalin present rather than the presence or absence of the compound. Knowing which genes give bean seedcoats their color is important to breeders because they now can more easily breed for particular colors that define the various market classes. The new data from our work is important to farmers because they may be able to market beans with particular flavonoid compounds which may help make beans easier to digest than beans without the flavonoids. Pharmaceutical companies may also benefit from our work because of the potential to extract particular flavonoids from bean seedcoats and market them as nutritionally important food supplements.
Technical Abstract: Three dry bean (Phaseolus vulgaris L.) genotypes differing in seed coat color, mineral brown (P C D J G B v), yellow brown (P C D J G b v) and pale greenish yellow (P C D J g b v), were analyzed phytochemically. Kaempferol 3-O-beta-D-glucoside (astragalin) was isolated and identified by NMR spectroscopy from all three genotypes, and was the main flavonoid monomer present. Flavonoid polymers (condensed tannins) were detected by thin laye chromotography, but anthocyanins were not detected in the three genotypes. High pressure liquid chromotography analyses indicated that astragalin was present at similar concentrations in pale greenish yellow and mineral brown genotypes, but was significantly lower in yellow brown. At present we do not know the functions of the G and B color genes, although the presence of astragalin in the three genotypes studied indicates that these genes do not appear to act in a qualitative manner with regard to astragalin production, ,but may control the amount of astragalin present. The subtle differences in color between these genotypes may be due more to the amount and type of tannins which have secondarily polymerized with phenolics and flavonoid monomers than the flavonoid monomers, per se.