Abstract: The objective of this study was to optimize the extraction process of protein from black rice by alkali extraction and acid precipitation. The optimal extraction process was established through controlling extraction conditions such as pH value,temperature,stirring rate,solid to liquid ratio,extraction time and particle size. Based on single factor experiments,four factor-three level orthogonal experiments were designed. The results showed that the effect of the investigated factors on the extraction yield of black rice protein was in sequence of pH value,particle size,solid to liquid ratio and stirring rate. The optimal extraction process of black rice protein was solution pH 12.5,temperature 28 ℃,stirring rate 800 rpm,solid to liquid ratio 1:10 g/mL,extraction time 1 h,acid precipitation 1 h,particles size 100 mesh. The extraction yield of water-soluble protein improved to 96.77% with the purity of 97.75%.

Key words: black rice protein, extraction yield, alkali extraction and acid precipitation, control variable method