The Influence Of Heat-Induced Aggregate On GEL Rheological Properties And Stability In Soybean Protein Solutions

Gelation is one of the most important properties for plant proteins, in this paper, we studied different environmental factors and aggregate characteristics (triggered by heating soybean proteins at90℃-30min and70℃-24h) on the gelling properties of soybean protein, acid-induced cold gelation and thermally stability were studied simultaneously.Gel network formation of soybean protein isolate was studied using small-strain dynamic rheological measurements. During the heating phase, the result revealed that1) the storage modulus (G’) and loss modulus (G ") were almost constant by tiny fluctuation below1Pa and2) the storage modulus was always smaller than the loss modulus until the gelling point was reached. Tan delta (δ) values decreased gradually in the heating phase, then followed by suddenly plunging to a very low level and remained constant at this low level of the entire cooling phase. This observation suggests that a stable gel network had formed. When both the heating and cooling rates were increased (from0.5to4℃/min), final G’ value decreased, indicative of decreased gel strength. The lower heating and cooling rates (0.5℃/min) resulted in smaller tan delta (δ), which hints the final product had the better three-dimensional structure compared to the high heating and cooling rate (4℃/min). The gelling point was dependent of heating rate but was unaffected by cooling rate. The higher protein concentration and pH resulted in the higher G’. Tan delta (8) and gelling point decreased with protein concentration increasing. Lower salt concentrations(0.1～0.2mol/L) lead to higher G’ and then decreased with increasing salt concentration. At a NaCl concentration2.0mol/L, tan delta (δ) was very higher and could not form a gel. Higher salt concentrations also lead to higher gelling points.The effect of aggregate characteristics on rheological properties of soybean protein dispersions was studied. Aggregated protein was produced by heating a solution of soybean protein isolate (SPI) at4%and9%w/v. The results showed that protein concentration played an important role in the properties of aggregates at the same heat treatment The higher protein concentration resulted in a larger aggregate size with a higher intrinsic viscosity and a higher accessibility of thiol groups. The protein fraction in native SPI had the smallest size and the lowest intrinsic viscosity. The same trend was observed for the shear viscosity after concentrating the suspensions containing aggregates to around14%w/v. Suspensions containing aggregates that were produced from a higher concentration possessed a higher viscosity. After reheating the concentrated suspensions, the suspensions produced the weaker gel, while the native soybean protein yielded the strongest gel.We evaluated the aggregate characteristics and disulfide bonding on acid-induced cold gelation rheological properties. Gelation (aggregate at70℃-24h) exhibited lower G’and turbidity compare to the cold gelation come from90℃-30min. NEM treatment of the aggregates had a big effect on the formation of disulfide bonds and clearly differ the storage modulus (G’) of the cold gelation.We evaluated the potential of soybean protein soluble aggregates to improve thermal stability in the presence of salts. Use of soluble aggregates improved thermal stability due to their higher charge, and resulted in final aggregates that were smaller and less dense, leading to reduced viscosity and turbidity compared to native soybean proteins.