Raman spectroscopic study of rice globulin

The conformation of rice globulin was studied by Fourier-transform Raman spectroscopy as influenced by different buffer environments and heat treatments. The Raman spectrum of the native protein showed a predominance of α-helical structures as indicated by major amide I and III bands at 1657 and 1270 cm−1, respectively. Highly acidic and alkaline pH conditions induced band shifts and intensity changes in amide I, amide III, and C–H (bending and stretching) vibrations, indicating protein denaturation. Addition of dithiothreitol and β-mercaptoethanol led to changes in S–S stretching vibration, whereas ethylene glycol and urea caused marked changes in tryptophan, tyrosine Fermi doublet and C–H band intensities. Heating at 100 °C resulted in progressive denaturation as indicated by band shifts and intensity changes of major spectral regions. Our results revealed that hydrophobic interactions and disulfide bonds play a major role in stabilizing the conformation and in thermal aggregation of rice globulin.