Study Of A New Preparation Method Of High-Quality Peptides From Rice Protein

Rice peptides have high nutrition value and great health function. The demand of rice peptides is strong and increasing fast at home and abroad. The content of oligopeptides is a key index to evaluate the quality of rice peptide products. The most common way to prepare peptides is enzymatic hydrolysis, due to its green and safety. At present, the preparation of rice peptides use mainly bath enzymatic hydrolysis. Due to its uncontrollable hydrolysis process, not only oligopeptides but also large quantities of non-oligopeptides were produced. This paper presents a study of controllable hydrolysis of rice protein to improve the oligopeptide content in rice peptides and prepare high quality rice peptide products. This study used broken rice as a raw material for the extraction of rice protein through alkali extraction and acid precipitation. Then, this study prepared rice peptides by the method of enzymatic hydrolysis. First, we screened a suitable enzyme for hydrolysis and optimized its hydrolysis conditions. Second, we studied the method of ultrafiltration-coupled enzymatic hydrolysis and compared its hydrolysis effects with bath enzymatic hydrolysis. The result demonstrated that the new method had great advantages in producing oligopeptides and improving the quality of peptide products.The results of comparing alkaline protease, neutral protease, acid protease and trypsin showed that alkaline protease was more suitable for the hydrolysis of rice protein. The conditions of hydrolysis were optimized via single factor and orthogonal experiments. The optimaized conditions of hydrolysis by alkaline protease were temperature 50 ℃, solid-liquid ratio 1:10, alkaline protease 1% and initial pH 10.5.The ultrafiltration-coupled enzymatic hydrolysis method was optimized. By comparing the performance of various ultrafiltration membranes, we chose regenerated cellulose membrane with MWCO 5 kD as the ultrafiltration membrane for the preparation of rice oligopeptides. Hydrolysis of 30 min was shown to produce the best results in terms of peptide yields and quality. Compared with bath enzymatic hydrolysis, the result demonstrated that ultrafiltration-coupled enzymatic hydrolysis had good effect on controlling hydrolysis process and increased the content of oligopeptides and peptides to over 60% and 70% respectively. The antioxidant capacity of rice peptides was also improved.In addition, the methods for determination of peptide molecular weight distribution and free amino acids were also studied. Mass spectrometry is an accurate, intuitive and quick determination method of molecular weight. However, compared with high performance gel filtration chromatography, mass spectrometry was not suitable for the accurate determination of molecular weight distribution due to the differences in ionization efficiency of peptides. So we selected high performance gel filtration chromatography method to determine peptide molecular weight and the relative content of oligopeptides. Compared with reversed-phase chromatography, it proved that high performance gel filtration chromatography could also determine the total content of free amino acids accurately. Use of high performance gel filtration chromatography to determine the total content of free amino acids has not been reported before.This study made a successful attempt on the preparation of rice peptides. It has important significance for improving the production level of rice peptides, promoting comprehensive utilization of rice resources and meeting user’s demand for high quality rice peptides.