Comparative study of structural and functional characterization of bran protein concentrates from superfine, fine and coarse rice cultivars.

Rice bran protein concentrates prepared from superfine, fine and coarse cultivars were assessed for their physicochemical, structural, functional properties and digestibility. The protein concentrates differed in structural, thermal and functional properties. Rice bran protein concentrate of fine cultivar (F-RBPC) had relatively more β-sheets (42.81%) and less α-helix (15.03%) and β-turns (21.98%) than that of superfine (SF-RBPC) and coarse (C-RBPC) cultivars. Thermal denaturation temperature (Td) was similar for all cultivars, whereas enthalpy of denaturation (ΔH) was high for F-RBPC. Essential and uncharged polar amino acids were the highest in F-RBPC and the lowest in C-RBPC. SF-RBPC had higher digestibility in comparison to F-RBPC and C-RBPC. Surface hydrophobicity, protein solubility and foaming capacity were greatest for F-RBPC. Whereas, SF-RBPC exhibited better foaming stability and emulsion activity and C-RBPC displayed more stable emulsion. Principal component analysis revealed that Td and ΔH were positively correlated with β-sheets content. Foaming capacity and protein solubility were related positively with surface hydrophobicity and negatively charged or uncharged polar amino acids. Emulsion properties were negatively correlated with hydrophobicity. In vitro digestibility of protein was negatively correlated to the ratio of Arginine to Lysine.