Gelation enhancement of soy protein isolate by sequential low- and ultrahigh-temperature two-stage preheating treatments

The effects of combined two heating steps with low (LT, 60 °C for 1 h) and ultrahigh (UHT, 130 or 140 °C for 4 s) temperatures on the thermal gelation of soy protein isolate (SPI) were studied. UHT pretreatments significantly increased protein solubility and enhanced the gelling potential of SPI. Yet, the two-stage preheating treatment with LT and then UHT-130 °C had a most remarkable effect: the gel strength of the SPI₆₀₊₁₃₀ sample was, respectively, 1.45-, 1.64- and 3.19-fold as strong as those of SPI₆₀, SPI₂₅₊₁₃₀, and SPI₂₅. In comparison with single LT or UHT treatments, this two-stage heating also produced greater amounts of soluble protein aggregates stabilised predominantly by disulphide bonds and hydrophobic forces, contributing to the improved gel network structure.