Study Of Antioxidative Peptide Of Traditional Fermented Soybean

Hydrolysis of protein in Douchi fermentation process is one of the important reactions of the flavor formation. Recent studies have shown that protein hydrolysis process produce antioxidant functional small peptides.Such small peptides can eliminate in vivo free radicals,have the function of anti-lipid peroxidation. Therefore, they become research highlights. Different microorganism, fermentation processes, geographical environments,production materials and other elements result in different antioxidative activity of soybean protein hydrolysates (SPH) in Douchi. Therefore,this study compare the antioxidant properties of different Douchi. Get a kind of Douchi which have good oxidation resistance and explore its oxidation resistance change during the process of fermentation.Lay the foundation for douchi functional product development.The results are as follows:1) This research selects15kinds of representative Douchi to test the total acid content, degree of hydrolysis, content of water-soluble protein, content of acid-soluble protein, brown stain index and total-antioxidant capacity (T-AOC). Moreover, the principal component analysis (PCA) is used for an analysis on relevance between quality indexes of various products and T-AOC. According to the analysis results, the relevance between quality index of various products and T-AOC is brown stain index>total acid content>degree of hydrolysis>content of acid-soluble protein>content of water-soluble protein. With respect to T-AOC index, Mucor fermented Douchi are superior to Bacteria fermented Douchi; dried Douchi are superior to wet Douchi; and Douchi in Mid-south regions are superior to that in southwest regions. According to the comprehensive conclusion, Huayue Aspergillus fermented Douchi have best T-AOC and PCA scores. Therefore, Huayue Aspergillus fermented Douchi are selected for subsequent research.2) Acetone-TCA method, Tris-HCl method and alcohol extraction method are used to extract SPH of Huayue Aspergillus fermented Douchi. According to the extraction results, after exclusion of interference from isoflavone, SPH extracted with the acetone-TCA method has higher extraction efficiency and T-AOC compared with SPH extracted with the other two methods, which indicates that it has favorable effects by using this method to extract SPH of Huayue Aspergillus fermented Douchi. 3) SPH of Huayue aspergillus fermented Douchi is subject to in vitro antioxidant evaluation, with400μmol/L Vc as contrast. SPH of Douchi is better in terms of inhibition O2.activity and OH activity, in the same level with inhibition to DPPH activity, reducing force, and anti-lipid oxidation capability, and poorer T-AOC4) Ultrafiltration and Sephadex G-25gel chromatography are selected for purification and separation of SPH of Douchi. According to the results, SPH molecular weight of Douchi is mainly concentrated within the range of3k-10kDa. Components<3KDa have good resistance to oxidation. For Sephadex G-25, Six components (Z1-Z6) are separated in best conditions, among which effective peptide components is Z1、Z2、Z3、Z4. Moreover, Z1, Z2and Z3have good antioxidant activity.5) A comparative research is made between Z1,Z2,Z3and SPH of Douchi in vitro antioxidant index and amino acid composition. According to the research results,Compared with SPH of Douchi, Zl, Z2and Z3are generally increasing with respect to antioxidant index and remarkably increasing in terms of inhibition to OH activity and O2activity. Amino acid composition of Z1,Z2,Z3and SPH of Douchi are mainly of Asp, Glu, Pro, Val,Lys and Met. With respect to the proportion of Val, Met, Lys and His in total amino acids, Zl, Z2and Z3have obvious increases when compared with SPH of Douchi.6) Huayue Aspergillus fermented Douchi during post-fermentation for0,15,30,45,60,75and90d are selected as objects of research to test in vitro antioxidant property of SPH of Douchi. According to the results, except inhibition to DPPH activity, other indexes rise first and then fall in the process of post-fermentation with respect to antioxidant activity. Inhibition to DPPH activity of SPH of Douchi keeps increasing and slowing down at45d of post-fermentation.According to the principal component analysis results, SPH of Douchi post-fermented for30d have good antioxidant activity.7) Huayue Aspergillus fermented Douchi During post-fermentation for0,15,30,45,60,75and90d are selected as objects of research for high performance liquid chromatography (HPLC) analysis. According to the analysis results, the molecular weight of SPH of Douchi is mainly concentrated between11000and300D during post-fermentation. In the whole process of post-fermentation, both content and variety of SPH are continuously increasing.