Effect of different degrees of milling on the protein composition in brown rice brans

In this study, the rice protein (RP) fractions (albumin, globulin, glutelin, and prolamin) in rice bran were obtained through the sequential extraction method using 2% (w/w) NaCl, 0.1 N NaOH, and 70% (w/w) ethanol and the proportions of water-soluble protein fractions (albumin) were compared among different degrees of milling (DM; 3%, 5%, 7%). The three types of bran showed different chemical components and populations of the four RP fractions. The 7% DM of brown rice is the stage at which the bran layers are completely removed and white rice is produced. In the 7%-DM bran, the content of water-soluble albumin was the highest. The extracted RP fractions contained eight essential amino acids and among them, albumin had the highest content of lysine. The secondary structures measured by circular dichroism spectroscopy were rich in alpha-helices. These results provide basic data for the extraction and utilization of water-soluble proteins from rice bran.