Study On The Formation Process And De-aggregation Of Insoluble Soy Peptide Aggregates

Soy peptide is an enzymatic hydrolysate of soy protein,which has antioxidant properties,antihypertensive effect and lipid metabolism promotion effect.However,during the hydrolysis of soy protein,soy peptide insoluble aggregates(ISPA)were inevitably produced,and this by-product accounts for 40%by weight,which greatly reduces the productivity of soy peptides.The original intention of this paper is to increase the yield of soy peptides.This paper compared the effects of different proteases on the enzymatic hydrolysis of soy protein isolate(SPI)and the formation of ISPA,and summarized the formation rules of ISPA.This paper discussed the functions of pH-shifting,ultrasonic treatment and emulsification to promoted the de-aggregation of ISPA,and compared the synergistic effects of the three methods.The main research contents and results of this paper are as follows:First,the effects of different proteases on the formation of ISPA were compared.In the process of enzymatic hydrolysis of SPI,Alcalase,Protamex and Flavor protease could produce24.2%,30.9%and 36.3%of ISPA,respectively.It was found that in solvents containing sodium dodecyl sulfate(SDS),the solubility of the three ISPA exceeded 90%with using different reducing agents to dissolved the three types of ISPA.SDS mainly broke the hydrophobic interaction force,indicated that the main intermolecular force of ISPA is the hydrophobic interaction force.ISPA has an anti-gastric digestion effect,but it has a higher intestinal digestibility in vitro digestion experiment.Amino acid analysis showed that ISPA are rich in various essential amino acids,and its nutritional value needs to be developed.Gel exclusion chromatography founded that the molecular weight distribution of the peptides combined into ISPA is similar to that of soluble soy peptides,and their relative molecular masses were between180 Da and 3 kDa,which indicated that ISPA is the result of re-aggregation of soy peptides during enzymatic hydrolysis.Secondly,in order to further clarify the formation process of ISPA,the change of the average particle size of ISPA and the change of the surface hydrophobicity of the hydrolysate within 4 h of enzymatic hydrolysis were studied.The results showed that the surface hydrophobicity rapidly increased to 3438.4 within 80 minutes during enzymatic hydrolysis.,indicating that the peptides produced during enzymatic hydrolysis contained a large number of hydrophobic amino acid residues.The average particle size of ISPA increased to 330.2 nm,indicating that the peptides gradually aggregated to form larger particles during enzymatic hydrolysis.However,the turbidity of the enzymatic hydrolysate under alkaline conditions continuously decreased from 0.9 to 0.1 with the extension of the enzymatic hydrolysis time,indicating that ISPA is easily soluble in alkali.When the pH of the enzyme hydrolysate was adjusted from 9 to 7,the content of ISPA changed from 2.7%to 24.2%.It showed that pH is the main factor affecting the rate of ISPA production.Finally,the effects of pH-shifting,ultrasound and emulsifiers on promoting the de-aggregation of ISAP were compared in order to increase the productivity of soy peptides.The three methods could increase the productivity of soy peptides from 74.5%to 84.6%,81.9%and78.5%,respectively.Among them,pH-shifting and ultrasound reduced the average particle size of soy peptides from 242.6 nm to 103.0 nm and 149.9 nm,respectively,so that the soy peptides in the enzymatic hydrolysis solution form a tighter structure.After using the de-aggregation method,the DPPH·and ABTS·~+radical scavenging ability of the enzymatic hydrolysate was improved,indicating that the de-aggregation method can dissolve the soy peptide contained in ISPA into the supernatant.Amino acid analysis showed that the three de-aggregation methods further accumulated hydrophobic amino acids(>40%)in ISPA,which indicated that the hydrophobic interaction force was the main reason for limiting the de-aggregation of ISPA.Furthermore,the comprehensive effects of the three de-aggregation methods were analyzed,and it was founded that the combined effect of pH-shifting and ultrasound had the greatest degree of ISPA de-aggregation,which increased the productivity of soy peptides from 74.5%to 86.4%.The soy target molecular weight peptide productivity(?3 kDa)increased from 68.8%to 77.5%,providing technical support and theoretical basis for optimizing the SPI enzymatic hydrolysis process and rational use of ISPA.