Thermal transition and decomposition properties of pH- and phosphate-induced defatted soybean meals

Defatted soybean meal is a popular raw material for soybean protein products. Thermal properties of soybean meal, which is vital for its application in extruded texturized soybean protein, are influenced by storage time and processing temperature. Thus, low-temperature defatted soybean meal (LSM), low-temperature defatted one-year-stored-soybean meal (LSSM) and high-temperature defatted soybean meal (HSM) were selected to investigate the thermal transition and decomposition properties by pH induction with phosphate using differential scanning calorimetry and thermal gravimetric analysis. The results showed that the peak temperature of 11S (glycinin) in phosphate buffer at pH 7 is significantly higher than that in deionized water. Break temperatures of LSM and LSSM at around 110 A degrees C in deionized water are significantly higher than that in phosphate buffer at pH 7; however, the break temperature of LSM at 300 A degrees C in deionized water is significantly lower than that in phosphate buffer at pH 7. In contrast to LSM, a dagger H of LSSM in phosphate buffer at pH 7 is significantly lower than in deionized water. It is thus concluded that phosphate stabilizes the soybean protein quaternary structure, enhances protein-protein interactions and weakens protein-water interactions. Protein association occurs in LSSM during soybean storage, while HSM protein appears to be insensitive to these changes.