Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/30/2003
Publication Date: 12/31/2003
Citation: Beninger, C.W., Hosfield, G.L. 2003. Antioxidant Activity of Extracts, Condensed Tannin Fractions, and Pure Flavonoids from Phaseolus vulgaris L. Seed Coat Color Genotypes. Journal of Agricultural and Food Chemistry. 51(27):7879-7883.
Interpretive Summary: Dry bean (Phaseolus vulgaris, L.) is an integral dietary component for a significant portion of the world population. Much research has been done on antinutritional factors present in beans, but the potential benefits of consuming beans from a 'health benefits' point of view have largely been overlooked. Seed coats of color seeded beans contain monomeric and polymeric phenolic compounds. Phenolic compounds present in natural foods may lower the risk of serious health disorders because of their antioxidant activity. An experiment was conducted to determine if the compounds extracted from 10 genotypes of dry bean with various seed coat color exhibited antioxidant properties. Three types of compounds; anthocyanins, condensed tannins, and flavonol glycosides, were extracted from the seed coats of dry bean. These compounds were then tested for their antioxidant activity using a type of fluorescence assay. The results of these tests showed that anthocyanins, quercetin glycosides, and condensed tannins had significantly higher antioxidant activity than BHT, a commercial antioxidant formulated in foods. Of the 10 seed coat colors used in the experiment, the compounds from beans from the light and dark red kidney market classes as well as beans with a yellow-brown seed coat color showed the highest amount of antioxidant activity. The beans with white or light yellow seed coats had the lowest activity. These findings suggest that colored seeded dry beans may be an important source of dietary antioxidants. Plant breeders may be able to develop new bean varieties with increased antioxidant activity and also, perhaps balance the positive effects of antioxidant activity with antinutritional effects, in diets.
Technical Abstract: Seed coat color of dry bean (Phaseolus vulgaris L.) is determined by the presence and amounts of flavonol glycosides, anthocyanins and condensed tannins (proanthocyanidins). To date, most work on P. vulgaris focused on the antinutritional effects of the seed coat polyphenolics but nothing had been reported on the beneficial effects these compounds may have, nor has there been any work published on the health benefits of phenolic monomers present in bean seed coats. There is increasing evidence that consumption of a variety of phenolic compounds present in natural foods may lower the risk of serious health disorders because of the antioxidant activity of these compounds. Flavonol glycosides, anthocyanins and condensed tannins were extracted from 10 genotypes with various seed coat color to determine if the methanol extracts and pure compounds extracted and identified exhibited antioxidant activity. The seed coat methanol extracts, tannin fractions, and pure flavonoids all displayed antioxidant activity in a fluorescence-based liposome assay. The relatively high activity of the condensed tannin (proanthocyanidin) fractions indicated that these compounds may play an important role in the overall activity of the extracts. Although polyphenols cause digestibility problems, they may have beneficial health effects. The pure anthocyanins, delphinidin-3-O-glucoside, petunidin-3-o-glucoside, and malvidin-3-O-glucoside and the flavonol, quercetin 3-O-glucoside, isolated from seed coats also had significantly higher antioxidant activity then the Fe2+ control. The activity of kaempferol 3-O-glucoside was not different from that of the Fe2+ control. Pure flavonoid compounds, such as anthocyanins, quercetin glycosides, and condensed tannins that are present in the seed coat of the common bean had significant antioxidant activity compared to BHT, a commercial antioxidant in foods. These findings suggested that colored seeded dry beans may be an important source of dietary antioxidants. Plant breeders may be able to develop new bean varieties with increased antioxidant activity and also, perhaps balance the positive effects of antioxidant activity with antinutritional effects, in diets.