Abstract: In order to improve the immunoactivity of enzymatic hydrolysates from extruded high-temperature soybean meal, the hydrolysis of the substrate by trypsin was optimized using central composite rotary design. Spleen lymphocyte proliferation (expressed as the stimulation index, SI) was investigated with respect to four variables including hydrolysis temperature, enzyme amount, substrate concentration and hydrolysis time. Using SPSS 13.0 and Design Expert 7.0.0, the experimental data were analyzed to determine the optimal hydrolysis conditions as follows: enzyme amount of 7999.97 U/g, hydrolysis temperature of 55.14 ℃, hydrolysis time of 4.34 h, and substrate concentration of 4.41%. Under the optimal hydrolysis conditions, the ConA-induced spleen lymphocyte stimulation index was determined by MTT method to be 1.1894.

Key words: high-temperature denatured soybean meal, central composite design, trypsin, immunoactivity