Effect of preheating-induced denaturation during protein production on the structure and gelling properties of soybean proteins

To explore the effect of preheating-induced denaturation during protein production on the structure and gelling properties of soybean protein isolates (SPI), protein neutralization solutions were preheated at various temperature for various periods and then spray-dried. The pre-denaturation degree (PDD) of SPI was quantitatively characterized by the change in the AB subunit using non-reducing SDS-PAGE. The onset denaturation time was 180 s, 40 s, and 10 s at preheating temperatures of 80 °C, 90 °C and 100 °C. As PDD increased, the contents of free sulfhydryl group and the ordered secondary structure gradually decreased, accompanied by the unfolding of the tertiary structure. Gel hardness, G′ and G″ increased at high PDDs, where the heating time required for gel formation decreased. The highly pre-denatured proteins (e.g., SPI86.11%, and SPI100%) formed gel network structures without heating. SEM images showed that the partially pre-denatured gels (SPI22.28% and SPI86.11%) were denser and had more uniform gel networks than the native protein (SPI0) and the completely pre-denatured protein (SPI100%). This work will provide guidelines for the control of heating conditions during SPI production process to improve gelling properties.