Rice bran protein hydrolysates exhibit strong in vitro α-amylase, β-glucosidase and ACE-inhibition activities.

Background: The objective of this study was to systematically examine the in vitro health-promotion activities of rice bran protein hydrolysates. Rice bran proteins were fractioned into albumin, globulin, prolamin and glutelin, which were subjected to hydrolysis by four protease preparations, namely Alcalase, Neutrase, Flavourzyme and Protamax, and the inhibitory activities of the hydrolysates against α-amylase, α-glucosidase and angiotensin converting enzyme (ACE), were monitored over a hydrolysis period of 240 min. Active peptides in the hydrolysates were isolated by ultra-filtration and ion-exchange chromatography and the peptide sequences of the active fractions were identified by LC-MS/MS.

Results: Hydrolysis of the proteins resulted in significant increases in these bioactivities, which were generally correlated with the degree of protein hydrolysis. In general, the highest bioactivities were found with albumin and glutelin hydrolysates, followed by globulin hydrolysates, while prolamin hydrolysates showed the lowest activities. Of the four enzymes used, Alcalase- and Protamax-catalysed hydrolysates generally had the highest activities while Flavourzyme-produced hydrolysates had the lowest activity. The MW < 3 kDa fraction of the Alcalase-catalysed glutelin hydrolysates had the highest β-glucosidase inhibition activity, which was identified to contain 13 peptides with six to 32 amino acid residues.

Conclusion: The α-amylase and α-glucosidase inhibitory activities of albumin and glutelin hydrolysates produced by Alcalase and Protamax were comparable in magnitude to those of the standard anti-diabetic drug acarbose, and had the potential to be developed into a dietary or nutraceutical supplement for the management of diabetes.