Phosphorylation Does Not Improve the Solubility of Rice Protein

摘要

The present study tried to phosphorylate rice protein (RP), a known insoluble food ingredient, and determine the improvement of its solubility. RP was allowed to react with sodium trimetaphosphate (STMP) at pH 11.5 and 35 degrees C, and the results indicated that 20.6% of the RP seryl residues were phosphorylated. Interestingly, the solubility of phosphorylated RP (2.6%) was not improved compared with that of RP (2.5%) at pH 7. The involvement of hydrophobic interactions and disulfide bonds in phosphorylated RP solubility was further evaluated. The phosphorylation of RP in the presence of urea as a chaotropic agent for weakening the hydrophobic effect resulted in 22.0% phosphoseryl residues but still did not increase RP solubility. The reduction of RP disulfide bonds prior to phosphorylation resulted in 31.3% phosphoseryl residues and increased RP solubility to 8.3% at pH 7, indicating that disulfide bonds within RP could be responsible for the failure to increase its solubility after phosphorylation.