Study On Characteristics Of Enzymatic Products Of Commercial Soybean Protein Isolate And Its Effect On Gel Properties Of Myofibrillar Protein

Enzymatic modification on soy protein isolate(SPI)can decompose large molecular proteins into small molecular peptides and amino acids,and improve its bioavailability and biological activity.However,the hydrophobic peptides produced during the enzymolysis process and the SPI residues that have not been completely enzymatically hydrolyzed are prone to aggregate to form insoluble aggregates(SPA),resulting in a low utilization rate.The subject of this research is to improve the utilization of SPI and SPA.The antioxidant activity of hydrolysats was first investigated,and then an electrochemical sensor was prepared for the antioxidant activity evaluation of the enzymatic hydrolysates of SPI(SPH)and determination of tryptophan(Trp)in SPH.Meanwhile,the surface and structural characteristics and formation mechanism were clarified and the utilization of SPA was investigated by studying the effect of SPA on the gel properties of myofibrillar protein(MP),which provided theoretical support and technical guidance for promoting the utilization of SPA during the industrial production.The main research contents and conclusions of this work are as follows:1.This chapter studied the enzymatic hydrolysis of SPI by Alcalase(Alc),trypsin(Try)or flavourzyme(Fla),or by a combination of flavourzyme with Alcalase(AF)or trypsin(TF).The results showed that AF and TF hydrolysis could significantly improve the enzymatic efficiency of SPI.SPH_Alc had the strongest antioxidant capacity,and the accumulation of antioxidant components in SPH_Try mainly occured in 0–1 h.The cyclic voltammetry(CV)results indicate that Trp contributes to the antioxidant capacity of SPH.2.This study developed a novel electrochemical sensor containing nitrogen-doped ordered mesoporous carbon(NOMC)for the quantification of Trp.The electro oxidation mechanism of Trp on NOMC/Nafion/glass carbon electrode(GCE)was first investigated,and was found to follow a two electron/two-proton transfer mechanism.The oxidation current was found to increase linearly with Trp concentration in the ranges 0.5–70.0?M and 70.0–200.0?M(different slopes in each range),with the limit of detection determined to be 35.0 nM(S/N=3).In addition,studies of Trp in real world systems,such as an 18 amino acid mixture and an enzymatic protein hydrolysate,showed excellent recoveries.Results suggest that NOMC/Nafion/GCE sensor has excellent performance characteristics for routine Trp analysis.3.The structure characteristics and formation mechanism of SPA were studied.The results showed that there was a transition from?-fold to?-helix and a negative correlation between?-helix content and surface hydrophobicity during the enzymolysis.Fla hydrolyzed aggregates(SPA_Fla)were mainly composed of slightly hydrolyzed SPI,the Alc hydrolyzed aggregates(SPA_Alc)and Try hydrolyzed aggregates(SPA_Try)contained large amounts of SPI residues and peptides with molecular weight less than 10 kDa.4.The effect of SPA on the gel properties of MP was studied and the formation mechanism of mixed protein gelation was explored.It was found that SPA_Alc,SPA_Fla,and AF hydrolyzed aggregates(SPA_AF)improved the gel strength and water holding capacity of the mixed protein gel,whilst SPA_Try and TF hydrolyzed aggregates(SPA_TF)obtained the opposite results.This research indicated that SPA_Alc,SPA_Fla and SPA_AF can be added into gel meat products as protein fillers to improve their texture characteristics and water retention.