Study On The Preparation Of Rice Peptides By Enzymatic Hydrolysis

Rice peptides have high nutrition value and great health function. The demand of rice peptides is strong and increasing fast at home and abroad. Rice peptides were prepared by enzymatic extraction in this study. The enzymatic preparation of rice peptide still needs to be studied further to increase the yield and reduce the bitter. In our work, the enzyme solution decolorizition, the detection methods, the dynamics of peptide extraction, the methods of improving the yield, the debittering methods and small-scale preparation of rice peptide were studied.In the research of peptide production, four important indexes are needed to be measured frequently for the optimization of the preparation technology. They are the content of peptides, the degree of hydrolysis, the content of free amino acids and the molecular weight distribution of peptides. Currently, these indexes are measured separately by different methods, so their measurements are time-consuming and inconvenient. In this study, a method through high performance gel chromatography was explored to simultaneously measure the four indexes at a time. The comparation revealed that good linear correlations existed between the quantitive results of the new method with those of the existed methods, the correlation coefficient was up to0.95, indicating the ability of the new method to simultaneously measure the four indexes.This paper compared the effect of the decolorization methods using active carbon, ultra-filtration, ammonium sulfate salting-out and ultra-filtration-coupled salting-out method. The result showed that the ultra-filtration-coupled salting-out not only had little influence on enzyme activity and protein concentration but also had excellent effect on decolorization. The decolorization rate reached91.99%. The activity of the enzyme was641.76U/mg and the total activity yield was82.08%.Low yield was a serious problem for the preparation of rice peptide by enzymatic hydrolysis. The effects of temperatures, time, initial pH, the amount of enzyme and solid-liquid ratio on the extraction of rice peptides were researched. The results showed that the rational conditions of enzymatic hydrolysis are50℃,4hours, initial pH11.0, the amount of enzyme was0.8%and the solid-liquid ratio was1:12. The yield of rice peptides was46.11%. The kinetics of the extraction process was studied by fitting the data and relation evaluation. A two-kinetic models and two-kinetic models were suited. The results showed that under certain conditions, the extraction rate of rice peptide hydrolysis with prolonged presence have theoretical maximum value.The effects of pH change, the dissolved state of rice protein and the competitive inhibition of product on rice peptide extraction rate were researched. It was found that the product’s competitive inhibition strongly affected the extraction yield of rice peptide. The results indicated that a step hydrolysis method combining alkaline and neutral protease could reduce the impact of the pH changes and product’s competitive inhibition on peptide extraction. The extraction rate of rice peptides significantly increased nearly20%. The prolyl endopeptidase was proved to hydrolyze hydrophobic amino acids of peptide terminu and therefore reduced the bitterness of peptide.A small-scale preparation of rice peptides was set up and a cellulose membrane with MWCO5kDa was used. The optimum conditions for the spray drying was500mL/h flow speed,120℃inlet air temperature. The peptide product had a good color and low bitter taste. The product contained48.76%oligopeptide (200～1200Da),76.4%polypeptide and21.76%free amino acids and DH was32.03%, indicating the rice peptides have excellent quality. We believe this study established an important basis for the application and popularization of the preparation of rice peptides by enzymatic hydrolysis in the future.