Abstract: In order to improve the color and functional properties of rice residue protein, response surface methodology was used to optimize parameters influencing its decolorization by hydrogen peroxide. The optimum decolorization conditions were hydrogen peroxide. concentration of 4.5%, pH 9.5, decolorization temperature of 55 ℃ and decolorization time of 45 min. Under these conditions, the whiteness of rice residue protein was improved from 20.5% to 48.2%. In addition, the lowest solubility (roughly 5%) of rice residue protein in pH 4－5 was observed. However, when pH was lower than 4 or higher than 6, the solubility of rice residue protein was significantly increased. The solubility of rice residue protein was 38.58% at pH 2 or 76.79% at pH 13. In neutral environment, the foaming capacity (FC), foam stability (FS), emulsifying activity index (EAI), emulsifying stability index (ESI), oil-holding capacity (OHC) and water-holding capacity (WHC) of rice residue protein after decolorization were 12%, 33.3%, 3.15 min, 24.84 min, 2.00 and 3.08, respectively. All of these values were much higher than those before decolorization. Therefore, hydrogen peroxide treatment can not only decolorize rice residue protein but also significantly improve its functional properties.

Key words: rice residue protein, hydrogen peroxide, decoloration, whiteness, response surface methodology