A biochemical analysis of mungbean (Vigna radiata) response to microbial polysaccharides and potential phenolic-enhancing effects for nutraceutical applications

Foods that contain plant phenolic secondary metabolites that are antioxidants are getting more attention due to an increase in experimental data suggesting health-promoting effects when such foods are ingested as part of a low-fat diet. As the synthesis of phenolic compounds in plants is known to increase during the defense response to microorganisms, we investigated specific food-grade microbial polysaccharides as potential elicitors of mungbean phenolic content. Mungbean (Vigna radiata) was pretreated with solutions of both xanthan and gellan gums, as well as commercial yeast extract and purified yeast glucan (as potential fungal elicitors), and dark-germinated for 1-5 days. Tissue samples were assayed for enzymatic (glucose-6-phosphate dehydrogenase and guaiacol peroxidase) and antioxidant activity, and for proline and phenolic content. Microbial polysaccharide treatments were found to stimulate phenolic content and enzyme activity, as well as occasional cotyledon pigmentation. In addition, xanthan gum, yeast extract, and purified yeast glucan treatments stimulated antioxidant activity. Possible mechanisms linking acid-induced plant growth to growth induced by food-grade microorganisms (and related polysaccharides), such as yeasts and acid-producing bacteria, are hypothesized and discussed.