Abstract: Rapeseed protein isolate was prepared on the basis of alkali-extraction and acid-precipitation combining with ultra-filtration. Through orthogonal tests, the best conditions of alkali-mullion and acid-isolation were: the pH 13, the temperature 40 ℃, the time of extraction 40 minutes, the times of extraction 3, the proportion of the material to liquid (g/ml) 1:10, 1:8, 1:6 respectively and the rapeseed protein deposited at pH 4.5. The conditions of the ultra-filtration to the separated liquid were: the temperature 40 ℃, the velocity of flow 2 m/s and the pressure 0.1 MPa. In the product gained through spray drying process,the content and recovery ratio of protein were 70.5%, 54.7% respectively.

Key words: rapeseed protein isolate, alkali-extraction and acid-isolation, ultra-filtration