Preparation And Solubilization Of Rice Dreg Protein Concentrates From By-Products Of Starch Syrups

By-product, named rice dregs, which was from rice flour that hydrolyzed by amylase in high temperature, was studied for preparation of rice dreg protein concentrates(RDPC) and solubilization of RDPC by proteases. From the point of view of kinetics, results showed that the solubilization of RDPC by proteases was fit for reaction of biphasic kinetics with liquid and solid phase. The main results were as follows:Firstly, the influence of liquefaction treatment on starch at high temperature was investigated. Results demonstrated that liquefying at high temperature leaded to the loss of albumins and globulins, the increase of surface hydrophobicity and molecular weight of proteins, the decrease of extraction efficiencies among various pH value. Microscopic analysis (SEM) proved that liquefaction treatment also broke the cell structure of rice endosperm and caused the melting of various rice components.Four methods, namely, base-extraction and subsequent proteolysis, water washing, enzymatic removal of sugars by non-amylase, and by amylase, were used to prepare rice dreg protein concentrates (RDPC) from rice dregs (RD). The fourth method gave the highest RDPC purity(87.7%). Microscopic observation confirmed that the effectiveness of amylase treatment in purifying RDPC from RD was due to hydrolysis of sugars. Gel filtration with different protein samples proved material and products made by various processing have different molecular weight distribution and different characters.Attention was also directed to the possible causations for the decrease of solubility after liquefaction treatment. presumably, the possible causations were as follows: loss of soluble proteins; increase of covalent bond (—S—S—) among proteins; extensive subunit aggregation and glycosylation, and so on.By comparison with the effect of solubilization of various proteolytic enzymes, Alcalase was ideal for industrial production. the optimal conditions were: concentration of substrate: 5%,Alcalase: E:S=0.8%,pH8.5, 55℃; Solubilization by protease made iso-electric solubility enhance along with hydrolysis time. At the beginning of reaction(10min), iso-electric solubility was enhanced evidently, and it kept on increasing until 60min, after that it did not improve markedly. From the point of view of kinetics, the mechanism of solubilization of RDPC included: enzyme interacted with RDPC suspensions partly by rapid adsorption onto RDPC particles, leading to solubilization of insoluble proteins, and partly by proteolysis of the protein fragments already in solution which have been cleaved by the adsorbed enzyme; product inhibited activity of enzyme; Experiment of addition of substrate in a batch reaction showed fresh substrate can be added to increase the extent of solubilization and better utilization of the enzyme, and it also suggested immobilized-enzyme recycle system can decrease product inhibition to enzyme activity. The initial reaction velocity equation was as follow: k2X1mK1[E]0[S]0 0.8859×[E]0[S]0V0 = ───────────────── = ──────────────────────1 + K1[E]0 + K1[S]0X1m 1 + 6.3027 [E]0 + 0.03590[S]0Gel filtration of hydrolysate showed hydrolysis of fraction of F1 was possibly fit for "All or None" model.