Thermal behavior and nonfreezing water of soybean protein components

Thermal denaturation and hydration of two soybean protein components were s tudied using differential scanning calorimetry (DSC). Results showed that t emperature of denaturation (T-d) Of both 11S and 7S globulins decreased sha rply with an increase in water content. Enthalpy of denaturation (Delta H-d ) of 11S increased with increasing water content at first, and then leveled off at high water content. However, Delta H-d of both 7S and 11S component s in 7S samples first increased and then decreased at high water content. T he preparation method of samples influenced the Delta H-d value significant ly but had little effect on the T-d. Nonfreezing water was determined from the DSC results. It increased in both 11S and 7S as water content increased but was more abundant in 7S, probably because of different compositions an d structures. Threshold value of water content for the appearance of freezi ng water was 0.3-.32 h (g of water/g of protein, mass ratio) for 11S. The w ater absorbed by both 11S and 7S during denaturation increased quickly at l ow water contents and remained almost constant at high water contents. The results were attributed to different structure and conformation of proteins before and after denaturation.