Characterization of Thermal Denaturation Structure and Morphology of Soy Glycinin by FTIR and SEM

The conformation and microstructure of soy glycinin were investigated by Fourier transform infrared spectroscopy and scanning electron microscopy after dry heating and autoclaving thermal treatments. The changes in frequency and signal intensity of infrared bands revealed the thermal denaturation on the solid-state structure of glycinin. The Fourier transform infrared spectral changes were subsequently assessed using the second derivative spectroscopy in the amide I region (1700–1600 cm−1). The bands at 1618 cm−1 and 1682 cm−1 were considered to reflect the formation of intermolecular and intramolecular aggregates (A1 and A2), and the contents of β -sheet indicated the degree of denaturation. In autoclaved samples, the contents of the glycinin α -helix, turn, random coil, and A2 significantly increased (P < 0.05), while the contents of the glycinin β -sheet and A1 significantly decreased (P < 0.05). The dry heating slightly affected the secondary structures of glycinin. The scanning electron microscopy results showed that the autoclaving treatment glycinin had denser and more uniform gel with homogeneous pores and heterogeneous granular structure, and the dry heating glycinin had crumbled multi-layered sheet like structure. The data suggested that the conformations of the autoclaved glycinins had more changes than dry thermally treated glycinins. While both dry thermally treated and autoclaved treated samples showed a high content in β -sheet structures which may adversely affect protein utilization.