Extractability of protein in physically processed rice bran

Commercially obtained defatted (DF), full-fat stabilized (FFS), and full-fat unstabilized (FFU) rice bran were processed by colloid milling and homogenization to affect bran breakdown and extraction of rice protein. Relative to unprocessed samples, there were moderate to slight increases in the amount of protein extracted from the various fractions of processed bran. Colloid milling and homogenizing slightly influenced the distribution of proteins in the various fractions obtained, with the FFU showing the greatest effect compared to DF and FFS protein fractions. The protein content of the supernatant fraction of FFU bran increased from 21.8 to 33.0% after colloid milling with a further increase to 38.2% after homogenizing, representing an overall increase of 75.2% in protein content. The supernatant fractions of DF bran increased from 13.9 to 14.7% after colloid milling, and to 16.5% after colloid milling and homogenizing, for an overall increase of 18.7%. Sodium dodecyl sulfate polyacrylamide gel electrophoresis showed a molecular weight distribution ranging from 6.0 to 97.4 kDa. Few detectable differences between protein bands of unprocessed and processed DF and FFU bran were observed. However, FFS bran showed breakdown in size distribution of protein after colloid milling and homogenizing, because certain high molecular weight proteins shifted to lower molecular weight units.