2.1 heat treatment method
Sorgentini et al. treated 5%, 8%, 11%, 13%, and 15% of soy protein isolate at 80°C or 100°C for 30 minutes, and then cooled at 4°C overnight. When the concentration was greater than or equal to 8%, a gel was formed. At the same temperature, the higher the concentration, the more insoluble components; when the concentration of the protein solution is the same, there are more insoluble components treated at 100°C than at 80°C. As measured by DSC, the protein was partially denatured when treated at 80°C, while the protein was completely denatured when treated at 100°C. After heat treatment, the surface hydrophilicity (S0) of the soluble and insoluble components of the protein changes. When the concentration is low, the internal hydrophilic groups are exposed due to thermal denaturation, and S0 increases. In the non-thermally denatured protein, the soluble and insoluble components have the same water binding capacity (WIC). After thermal denaturation, the WIC of both the soluble and insoluble components increase, especially at the highest concentration of 8%. After heat treatment, the emulsification performance of protein South is improved.
L0pezde Ogara et al. In the process of alkaline extraction and acid precipitation to prepare soy protein isolate, the pH value of the solution was adjusted to the isoelectric point and then treated in an aqueous solution of 50°C, 60°C, 65°C and 70°C for 30 minutes. Protein solubility (NSI) decreases, water absorption (WAC) increases rapidly when the temperature rises from 50°C to 60°C, and decreases slightly when the temperature continues to increase. After heat treatment, the oil absorption is slightly increased. The gel obtained from the protein obtained at 60°C has the highest viscosity and the lowest water loss.
2.2 acid treatment
Wagner et al. treated soy protein isolate and Glycinin with acid. Only the protein extracted from the soybean meal stored for a long time, the solubility will be reduced after acid treatment, the change of pH has little effect on the solubility and water binding capacity (WIC), and the foaming and foam stability are very large. improve. During acid treatment, the pH value of 11S globulin has a strong denaturation effect.
2.3 Enzyme treatment
Wu et al. used papain to hydrolyze soy protein isolate and ultrafiltration to separate the hydrolysate. The 11S protein subunit is more sensitive to papain than the 7S globulin. Papain significantly improves the surface water absorption, solubility and emulsification of soy protein isolate.
QI et al. studied the hydrolysis of soy protein isolate by trypsin. Trypsin includes trypsin and chymotrypsin, which can hydrolyze the two basic subunits of 11S soy glycinin. After the soy protein is hydrolyzed by trypsin, the surface water absorption (S0) is significantly improved, the solubility changes little, the protein and oil content of the emulsion increases, the emulsifying ability increases, but the emulsifying stability decreases.