Preparation of Heat-Resistant Peptides from Hongqu Rice Distiller’s Grains and Its Effect on the Thermally Induced Oxidative Tolerance in Saccharomyces cerevisiae

Abstract

Thermally resistant peptides were obtained from enzymatical hydrolysis of Hongqu rice distiller’s grains and evaluated for its effect on resistance to thermally induced oxidative stress in Saccharomyces cerevisiae. Various proteases were screened for the survival rate of S. cerevisiae under heat stress. The enzymatic hydrolysis conditions were optimized based on the yield of thermally resistant peptides, and the peptides were identified by mass spectroscopy and its antioxidant activity was investigated. The expression of genes in the pentose phosphate pathway and the contents of intracellular coenzyme, glutathione (GSH) and reactive oxygen species (ROS) were analyzed to explore the protective effects of the peptides on S. cerevisiae from heat-induced oxidative stress. The results indicated that the optimal enzymatic hydrolysis conditions were as follows: Hongqu rice distiller’s grains/water ratio 1:10, hydrolysis temperature 50 ℃, hydrolysis time 3 h, protamex dosage 3 000 U/g, and pH 8.5. Under these conditions, the yield of thermally resistant peptides was 62.44%, and the survival rate of S. cerevisiae in the presence of the prepared peptides under heat stress was 73.97%, which was 22.76% higher than that of the control group (pure water). Sequence identification showed that 16 out of the top 20 most abundant peptides had hydrophobic amino acid contents of over 50%. The peptides exhibited 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) cation radical scavenging activity with a half-maximal effective concentration (EC50) of 4.53 and 1.82 mg/mL, respectively, indicating good antioxidant activity. Besides, the thermally resistant peptides upregulated gene expression in the pentose phosphate pathway, elevated NADH kinase activity, increased GSH content by 5.74 times, and restored intracellular ROS to almost the same level as before heat stress treatment, thus enhancing resistance to heat-induced oxidative stress in S. cerevisiae.

Keywords

• hongqu rice distiller’s grains; thermally resistant peptides; thermally induced oxidative stress; saccharomyces cerevisiae