Submitted to: Michigan Dry Bean Digest
Publication Type: Trade Journal
Publication Acceptance Date: October 15, 1997
Publication Date: N/A
Interpretive Summary: Consumers are increasingly concerned about what foods they eat and have been making food choices based on elements present in food which are seen as beneficial to health. A common example is Vitamin C (ascorbic acid) found in citrus fruits, which is a natural antioxidant that may contribute to lower instances of certain forms of cancer. There are color compounds, called flavonoids, present in bean seed coat that may be beneficial to health in terms of antioxidant activity, but may also have unwanted effects on digestibility. It is therefore necessary to identify the compounds responsible for seed coat color, relate these to the genes that control them, and determine their antioxidant activity as well as effects on digestibility. Extracts containing flavonoid compounds from seed coats of several market classes of bean were all found to have excellent antioxidant activity. In a digestibility study a bean with a yellow seed coat was the most digestible of all beans tested. Flavonoid compounds from several of the market classes and from beans with the yellow seed coat have been isolated and identified for further testing. Knowledge of the type of flavonoid compounds present in beans is essential to providing consumers with information on possible health benefits that can be derived from including beans in their regular diet. This information also provides plant breeders with a genetic basis on which to enhance the antioxidant activity of beans and at the same time improve digestibility through selection.
Technical Abstract: Flavonoids are a class of phenolic compounds responsible for a wide range of colors in plants. Seed coat color in common bean, (Phaseolus vulgaris L.) is the result of a mixture of distinct flavonoid compounds. Identification of the genes for seed color has been known for some time, but the combinations and amounts of flavonoids produced by the different genes is not known. Also of interest is the antioxidant potential of seed coat flavonoids and what effects various colors have on whole bean digestibility. Dietary flavonoids are known to protect phospholipid bilayers when exposed to free radicals. We examined five bean genotypes that correspond to "white", "yellow", "brown", "red" and "black" market classes. All of the methanolic extracts from the white, brown and black genotypes showed very good antioxidant activity in a liposome oxidation study. In digestibility studies the yellow class of beans was found to be 30% more digestible than navy beans and greater than 60% more digestible than black beans. In an analysis of the chemistry of bean color classes, it was determined that the flavonol, kaempferol, is common to all of the brown lines and that kaempferol glycosides are found in the yellow bean line. It may be possible to enhance the antioxidant activity of beans and also improve digestibility through plant breeding.