Anitoxidant Study On Glycinin Hydrolysates And Preparation Of Thiol Peptides

In biological systems, cysteine residues in proteins play several important roles, SH cancoordinate metal binding, play the role of antioxidant, restore thiol homeostasis and promotethe flavor substances in flavour. It will be of broad prospect to obtain thiol-rich peptides fromcheap source of glycinin, while SH can be oxidized to SS, SOH and others to change thefunctional properties, it is of great importance to accurately determine the SH content, have agood understanding of the behaviors of cysteine residues in enzymatic hydrolysis and obtainthe thiol-rich petides by isolation methods.We firstly studied the relationship between thiol and antioxidant activity, and theproperties of enzymatic hydrolysates of soy glycinin with reduction, including DH, molecularweight and antioxidant activity were better than the ones without reduction. We studied thequantitative relationship between thiol content and antioxidant activity, we found that thereare linear relationships between thiol content and them. In addtion, we came to a conclusionthat reduced glycinin hydrolysates obtained by pepsin have better capacity of inactivation oftrypsin inhibitor, which was in the order of DTT>Cys>peptide>GSH.The method for determining SS content in hydrolysates was studied. Firstly, weoptimized the methods and did the screening using a standard glycinin hydrolysate, thenfurther studies were done using hydrolysates with different DHs, finally, we proved theconsistency between indirect and direct methods for the determination of SS. Conditions fordeterminte TSH are as follows:0.8mol/L BH in the final concentration,6mol/L GuHCl fordenaturant, reduction for50℃,30min.The changes of soybean glycinin SH and SS in enzymatic hydrolysis by pepsin, neutrase,and alcalase were studied. Firstly, the behaviors of glycinin SH, SS, TSH by three proteaseswith different DHs under certain condition and by alcalase with different temperatures andpHs were examined, then behaviors of reduced glycinin SH in the enzymatic hydrolysis withdifferent enzymes amount were studied. The results showed that the SH, SS, and TSHcontents are all significantly decreased with increasing pH or temperature and the SH loss wasenhanced in the order of pepsin, neurase, and alcalase.Fractions of reduced glycinin hydrolysate obtained by pepsin using IEC were studied.We optimized the conditions for separation: eluant pH4.0, loading quality:200mg/mL1ml,0,0.01,0.05,0.2,0.5,2mol/L NaCl. The larger molecular weight peptides and basic aminoacid content increased as the salt concentration increasing. It was found that the0mol/L NaClfraction recovered about6.3%peptide and28.8%SH, and contained the highest SH contentof498.0μmol/g, most of the thiol-rich peptides are acid small weight molecular peptides.