Infrared and Raman spectroscopic characterization of structural changes in albumin, globulin, glutelin, and prolamin during rice aging.

Structural changes in albumin, globulin, glutelin, and prolamin from fresh and aged rice were characterized in this study. Infrared and Raman spectroscopies revealed changes in interactions between protein and starch, and the occurrence of structural changes involving secondary and tertiary structures of protein induced by rice aging. The α-helical structure was reduced, and aliphatic amino-acid side chains became more buried in albumin after rice aging. Oxidation of the sulfhydryl group in globulin was evident. The unordered coil in glutelin decreased, and a characteristic frequency of the free sulfhydryl group appeared. The antiparallel β-sheet in prolamin increased, the conformation of disulfide bonds changed, and tyrosine residues became exposed to a polar environment. The association between globulin and starch strengthened, whereas that between glutelin and starch diminished. These differences in structure and interactions with starch might be responsible for the dissimilar pasting properties between fresh and aged rice.