Ultrasound-Assisted Multi-Enzymatic System for the Preparation of ACE Inhibitory Peptides with Low Bitterness from Corn Gluten Meal

Yunliang Li,Wenjuan Qu,Haile Ma,Siyu Ruan,Yanhua Ding,Xiaofei Ye,Shanfen Huang,Chengliang Li

doi:10.3390/pr9122170

Abstract

The promising angiotensin converting enzyme (ACE) inhibitory peptides derived from corn protein usually have strong bitterness and thus limit their use among consumers. To prepare ACE inhibitory peptides with low bitterness, two energy-efficient types of ultrasound pretreatment were introduced into the multi-enzymatic system of corn gluten meal. The results showed that Flavourzyme–Protamex sequential enzymolysis produced the peptides with high ACE inhibitory activity and the lowest bitterness compared with other enzymolysis conditions. During the optimized sequential enzymolysis, the divergent ultrasound pretreatment with a frequency of 40 kHz for 60 min exhibited higher ACE inhibitory activity (65.36%, accounting for 73.84% of the highest ACE inhibitory activity) and lower bitterness intensity of peptides, compared with an energy-gathered ultrasound. The results of the study showed that, on the one hand, divergent ultrasound pretreatment induced the highest intrinsic fluorescence of protein, with more hydrophobic amino acid residues exposed for cleavage by exopeptidases, which leads to a reduction in bitterness. On the other hand, the amino acid composition analysis proved that more Tyr, Ile, and Val moieties, instead of Leu (bitterest substance), and more peptide fractions with a molecular weight >1000 Da should be the structural features of high ACE inhibitory peptides.

Highlights

Corn has an eminent position in food crops across the world
The angiotensin converting enzyme (ACE) inhibitory activity of the corn gluten meal hydrolysates (CGMHs) produced from Neutrase-Protamex (NP) sequential enzymolysis varied from 19.29% to 88.51%, and the highest ACE inhibitory activity value, at 88.51%, was obtained after 40 min of Neutrase hydrolysis
The CGMHs obtained by Alcalase-Protamex (AP) sequential enzymolysis had various ACE inhibitory activity ranging from 40.89% to 69.37%

Summary

Introduction

Corn has an eminent position in food crops across the world. Corn gluten meal is the major by-product of the corn starch process [1]. The enzymes commonly used in the preparation of ACE inhibitory peptides are endopeptidases, such as Alcalase and Neutrase These endopeptidases release peptides by cleaving hydrophobic amino acid peptide bonds in the protein chain, resulting in the N- and/or Cterminus of the ACE inhibitory peptides containing hydrophobic amino acid residues (i.e., Leu, Ile, Val, Tyr, Phe, and Trp) [8]. The contribution of hydrophobic amino acid residues at the N- and/or C-terminus to the bitterness can be evident, probably owing to their binding to the human taste G-protein coupled receptors followed by the activation of associated organoleptic signaling processes [10] These ACE inhibitory peptides always have a pronounced bitter taste [11,12,13], which impedes their acceptance by consumers and limits their utilization in the food industry. Systematic research on both ACE inhibitory activity and the bitterness of peptides is unavailable

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