Characterization and Analysis of Protein Structures in Oat Bran

Globulin, albumin, gluten, and gliadin in oat bran were prepared by the Osborn method using oat bran as starting material. We characterized the secondary and tertiary structures of 4 proteins using circular dichroism, Fourier-transform infrared spectroscopy, and fluorescence spectroscopy in order to analyze the composition and functional mechanisms. The results showed that the amino acid composition in all the 4 proteins was relatively balanced, and the essential amino acid content in albumin and globulin was high. The molecular weights of albumin, globulin, gliadin, and gluten were 19 to 21, 15 to 53, 20 to 38, and 10 to 90 kDa, respectively. The composition of gluten was a little complex compared to those of the other oat bran proteins. The secondary structure distribution of the 4 proteins differed, and increase in the pH resulted in modification of the β-sheet structure to α-helical structure. Moreover, the α-helix content and surface hydrophobicity were negatively correlated (r = -0.988, P < 0.05). The peak position (λ_max ) and intensity of the fluorescence spectra of 4 proteins were in the order of gliadin > globulin > gluten > albumin, indicating that surface hydrophobicity of gliadin was the strongest and that of albumin was the weakest among the 4 proteins.