The Study Of Emulsifying Property Of Protein In Soy Sauce Residue And The Antioxidant Activity Of Hydrolyzate

Soy sauce residue is Chinse rich resource, which contains large amounts of nutritious,physical and chemically active substances, such as protein and dietary fiber. It has not beenfully utilized so far. This study investigated the best extraction technology of soy sauce residueprotein, and antioxidant activity of protein hydrolyzate. The emulsifying activity and stabilityof the soy sauce residue protein isolated, soy protein isolated and the glycosylated soy proteinwere comparatively analysized. This study also investigated the physico-chemical properties ofpurified protein samples. This study provided a theoretical basis for further utilization of soysauce residue resources, and expanded the application scope of it.Firstly, the extration technology of protein from soy sauce residue was studied. The bestcondition was: pH=10.97,52.7℃,54.3min; the exctraction rate was74.03%. In single factors,the pH (A), time (B), temperature (C) significantly affected the extraction rate (p <0.01); duringthese interaction of two factors, AB (p <0.05), AC (p <0.01) demonstrated a significantinfluence level. The protein was proved to be a glycoprotein by the Sevag reagent method, andtotal sugar content and protein content ratio was1:1.4.This study continued to gain purified proteins by DEAE-Sepharose-FF ion exchangecolumn, and respectively, the molecular weight of the four purified protein sample were10943.8Da，16507.98Da，147146.5Da，365306.2Da which were eluated by0.2mol/L,0.4mol/L,0.6mol/L,and1.0mol/L NaCl-Tris-HCl buffer.The pI of SRP was around pH3.5, so in acidic environment SRP also maintained goodsolubility, and emulsifying activity was significantly higher than the SPI and GSP. In high saltenvironments, GSP and SPI`s emulsifying activity and emulsion stability decreasedsignificantly; but the SRP`s emulsifying activity decline slowly. When NaCl`s concentrationwas0.3mol/L, emulsifying activity of SRP ws1.77times higher than that of the SPI.Based on the previous study, the emulsifying activity and emulsion stability of eachcomponent were studied. The hydrophobicity of the SRP was2.55times than that of SPI; thehydrophobicity of SRP-1and SPI was very close; respectively, the hydrophobicity of SRP-2,SRP-3, and SRP-4were3.01times,2.52times and2.3times than that of SPI. Mastersizer2000 particle size distribution was utilized to measure the particle size of emulsion droplet by theprotein samples and oil. At the conditions of pH=7~9, emulsion particle size increased slowly.The emulsifying capacity and stability of SRP-2, SRP-3and SRP-4, were significantly betterthan those of SPI. Overall, in comparison, the emulsifying properties wasSRP-4≈SRP-3>SRP-2>SRP-1≈SRP>SPI.The enzymatic hydrolysis of six protease against soy sauce residue protein was studied toobtain a highly antioxidant-active bioactive peptides. Neutral protease, Protamex and Alcalasealkaline protease were selected to comprise the hydrolyzing-system. The hydrolyzate`santioxidant activity was the indicator to decide the best technology: Alcalase+neutral proteasewere added at the amount of6000U/g, when pH=8.0,60℃, for2h. The resu lts indicatedthat the antioxidant capacities of hydrolyzate increased with its concentration. Whenhydrolyzate dosage was10mg/mL, the reducing power, antioxidant activity, scavenging activityofO2, OHand DPPH free radical reached56.05%,85.05%, and82.11%respectly.