Enhancement of rice protein hydrolysate quality using a novel dual enzyme system

Abstract

Currently, the bitterness of rice protein hydrolysates has limited their use as food ingredients or additives. The objectives of the present study were to use dual enzyme hydrolysis to produce rice protein hydrolysates with reduced bitterness and high nutritional value. In this study, Streptomyces canus T20 aminopeptidase (ScAPase) was first expressed in food-grade expression host Bacillus subtilis, obtaining a specific activity of 6217 nkat/mg protein. ScAPase showed high specificity for peptides containing Leu, and Val residues at the N-terminus, indicating that its activity is significantly affected by the nature of the penultimate and antepenultimate residues of substrates. The dual enzyme system involved the synchronous treatment of RPI with trypsin (0.2 g/g RPI) and ScAPase (0.03 g/g RPI) at 50 °C for 4 h to produce small peptide-RPI hydrolysates (STRH, 3.37 mg/mL), without any bitterness. Moreover, STRH showed high inhibitory activity of angiotensin-converting enzyme (57.2%) and scavenging activity of radicals, such as ABTS+· (90.1%), O2−· (82.0%), and DPPH (50.8%). Thus, this novel, environmentally friendly dual enzyme system has the great potential to enhance the quality of RPI hydrolysates by enriching small peptides, decreasing bitterness, and producing bioactive peptides.