The Effect Of High Solid Concentration On Characteristics Of Enzymatic Hydrolysis Of Soy Protein Isolates

Enzymatic hydrolysis technology is an effective way to improve protein’s functionality and prepare high biological activity polypeptides. At present, protein hydrolysis in industrialized production was performed at low solid concentration from10%- 20%. Working at low solid concentrations has the advantages of convenient operation and lower requirements for equipments. But with the development of enzymatic hydrolysis technology, the disadvantages of low solid concentrations manifest more and more, such as lower equipment utilization rate and higher water, energy, labour and captital costs. This study focused on the effect of high solid concentrations on characteristics of enzymatic hydrolysis of soy protein isolate, aiming at finding a new way to enhance the added value of protein.The solid concentration affected the physicochemical properties of SPI solution. High solid concentrations resulted in higer viscosity and lower fluidity. The results showed that fluidity of protein system increased and viscosity decreased at pH 3.5. The solubility of the SPI decreased and the difference of the solubility between natural pH and pH 3.5 narrowed for increasing solid concentrations. The particle distributions, secondary structure, SDS-PAGE were used to evaluate state of protein at different solid concentration. It showed that protein aggregation occurred at high solid concentration.This study provided an objective measurement for hydrolysis efficiency of high solid concentration. The degree of hydrolysis was measured without sedimentation but protein recovery need to be diluted to lower concentration and centrifuged. There is no evident effect on amino acid conversion rate whether hydrolysate was diluted or not. After single factor experiments, the optimal technological conditions of enzymatic hydrolysis of SPI in high solid concentration were as follows: Flavourzyme,pH:6.5,hydrolysis tempreture: 50 ℃,the amount of protease: 1%; the acid protease,pH:3.5,hydrolysis tempreture: 55 ℃,the amount of protease: 1%.After enzymatic modification of SPI, the acid protease was preferred to Flavourzyme in the results of hydrolysis. In addition, high solid concentrations resulted in a higher weight fraction of macromolecule. SDS-PAGE results showed that flavourzyme was not sensitive to 11 S but the acid protease was sensitive to 7S and 11 S. We found that enzymatic hydrolysis of SPI could increase the solubility, the disperse stationarity, the foaming capacity and decrease the water binding capacity, the emulsifying ability, the foam stability respectively. The results showed that the solid concentrations during proteolysis did not affect the solubility and the disperse stationarity of the hydrolysates prepared by flavourzyme while the solubility of the hydrolysates by the acid protease decreased and the disperse stationarity increased with increasing solid concentrations. At the same DH%, high solid concentrations showed higer water binding capacity and emulsifying ability. The foaming capacity was lower for SPI hydrolysates prepared with low solid concentration whereas hydrolysate from high concentration at DH %< 9%. It demonstrated the opposite result when the DH %> 9%.Under the optimal technological conditions of the acid protease, we get the peptides with different DH %. The hydrolysis rate was independent of the solid concentration at DH <11% but did depend on the solid concentration at higer DH %. Furthermore, the solid concentration did not affect the amino acid conversion rate at the same hydrolysis time. The peptide molecular weight of the SPI hydrolysates at a DH% of 21.5% was mainly smaller than 3000 Da; the content of amino acid which could have resistance to oxidative condition was over 64%. The hydrolyzate prepared for high solid concentration show higher antioxidation activity.This research got the soy peptide with high antioxidation activity. The enzymatic hydrolysis condition: solid concentration 32%, DH% 21.5 %( hydrolysis time 30.5 h). The IC50 value of DPPH radical scavenging activity and Hydroxyl radical scavenging of hydrolyzate were 3.80 mg/m L and 20.03 mg/mL, reducing capability was 0.647, Fe2+-chelating activity was 89.4%.