Effects Of Two Enzymes On The Freeze-Thaw Stability Of Soy Protein

Soybean protein isolate(SPI) is a low temperature defatted bean pulp as raw material to produce the full price of protein, the protein content as high as 90%, rich in 8 kinds of essential amino acids, and the amino acid score close to animal protein, is one of the best plant protein replacing animal protein. In this paper, soybean protein isolate as raw material, were investigated the influence of papain limited hydrolysis(DH≤4%) and phytase-papain synergy modification(DH≤4%) on emulsion freeze-thaw stability, to get the freeze-thaw stable soybean protein isolate to be applied in frozen foods. In addition, through the hydrolysates gel electrophoresis analysis to explore the mode of protein enzymolysis and functional characteristics changes in internal relations, which is the key to reveal the nature of the functional changes.The test to determine the papain conditions of restrictive hydrolyzed soybean protein isolate, the degree of hydrolysis as index, to get the hydrolysis parameters: temperature 50 ℃, p H7.0, enzyme dosage 7000 U/g, the substrate concentration of 3%. Under th is condition, the preparation of restrictive hydrolysate(DH1, DH2, DH3, DH4), analyzed hydrolysate structure(solubility, free amino content, protein secondary structure, SDS-PAGE electrophoresis). With particle size, oiling off, creaming index, flocculation and aggregation degree as the index, investigate the influence of enzymatic hydrolysis degree on emulsion freeze-thaw stability. The results showed: papain hydrolysate emulsion has a good freeze-thaw stability, and with the increase of hydrolysis degree, the freeze-thaw emulsion creaming index and oiling off showed a downward trend.The test to determine the phytase-papain conditions of restrictive hydrolyzed soybean protein isolate the nitrogen yield as index, to get the hydrolysis parameters: time 45 min, enzyme dosage 1000 U/g. Under this condition, the preparation of restrictive hydrolysate(P-DH1, P-DH2, P-DH3, P-DH4), analyzed hydrolysate structure(solubility, free amino content, protein secondary structure, SDS-PAGE electrophoresis). With particle size, oiling off, creaming index, flocculation and aggregation degree as the index, investigate the influence of enzymatic hydrolysis degree on emulsion freeze-thaw stability. The results showed: the method of phytase-papain hydrolyze furtherly improved the freeze-thaw stability of emulsions, and P-DH4 emulsion creaming index was 18.27%, oiling off was 12.52%, flocculation degree was 49.12%, aggregation degree was 80.66% lower than that of SPI, emulsion showed good freeze-thaw stability.The effects of various environmental stresses, such as p H, Na Cl concentrations and the freeze-thaw cycles on the stability of emulsions were examined. The results showed that the freeze-thaw stability of phytase-papain hydrolysate(P-DH4) emulsion been significantly improved in the p H range of 3.0 to 10.0. Moreover, the hydrolysate emulsion also showed the characteristics of the salt tolerance, the emulsions in 0 ~ 500 mmol/L Na Cl concentrations have better freeze-thaw stability. Emulsion droplet morphology diagram showed that the hydrolysate emulsions can maintain the stability of the emulsion after three times of freeze-thaw cycles without obvious aggregation and creaming.