Anti-diabetic and anti-hypertensive potential of sprouted and solid-state bioprocessed soybean.Asia Pac J Clin Nutr. 2005; 14(2):145-52.AP
Long-term type 2 diabetes can lead to numerous biological complications, such as hypertension and cardio-vascular disease. Key enzymes involved in the enzymatic breakdown of complex carbohydrates,pancreatic alpha-amylase and intestinal alpha-glucosidase, have been targeted as potential avenues for modulation of type 2 diabetes-associated post-prandial hyperglycemia through mild inhibition of their enzymatic activities so as to decrease meal-derived glucose absorption. Further, inhibition of hypertension-linked angiotensin I-converting enzyme (ACE) was targeted as a potential approach for modulation of diabetes-linked hypertension. Water-soluble extracts of soybean optimized for phenolic content via sprouting or bioprocessing by dietary fungus (Rhizopus oligosporus, Lentinus edodes) were investigated for inhibitory activity against porcine pancreatic alpha-amylase (PPA), yeast alpha-glucosidase, and rabbit lung ACE in vitro. PPA was allowed to react with each phenolic-optimized extract and the derivatized enzyme-phytochemical mixtures obtained were characterized for residual amylase activity. Alpha-glucosidase and ACE activities were determined in the presence of each phenolic-optimized extract. All of the soybean extracts possessed marked anti-amylase activity, with extracts of R. oligosporus-bioprocessed soybean having the strongest inhibitory activity, but only slight anti-glucosidase activity. The anti-amylase activity of each extract seemed associated with extract antioxidant activity. Anti-enzyme activity was slightly associated with total soluble phenolic content per se, but seemed more associated to the length of sprouting or bioprocessing of the soybean substrate. Short-term sprouting or bioprocessing seemed to improve anti-amylase activity, while long-term sprouting or bioprocessing seemed to aid anti-glucosidase activity. While ACE activity was strongly inhibited by all of the soybean extracts (44-97%), only sprouting was found to increase this inhibition and bioprocessing of soybean with L. edodes decreased inhibitory activity of soybean extract. The results suggest that sprouting and dietary fungal bioprocessing of soybean improve the anti-diabetic potential of soybean extracts, potentially through modulation of the phenolic profile of the extract, and further suggest that enzyme inhibitory activity may be linked to phenolic antioxidant mobilization during spouting and/ or bioprocessing. The significance of food-grade, plant-based enzyme inhibitors for modulation of carbohydrate breakdown and control of glycemic index of foods in the context of preventing hyperglycemia and diabetes mellitus complications such as hypertension in the long-term is hypothesized and discussed.