Abstract: According to the degree of hydrolysis (DH) and sensory evaluation, effects of pretreatments on soybean meal was studied and the optimum hydrolysis condition was analyzed by single factor experiments and response surface optimization. The soybean meal was pretreated by pressurization, ultrasonic treatment, microwave irradiation treatment and heating treatment, respectively. The results showed that the heating treatment, with temperature of 80 ℃ and time of 10 min, was suitable for the pretreatment of soybean meal. According to DH and sensory evaluation, the compound enzyme for soybean meal hydrolyzing was the mixture of neutral protease and protamex with ratio of 2:3. The optimal hydrolysis condition of compound enzyme was obtained by single factor experiments and response surface optimization. The results showed that optimum hydrolysis condition was as follows: pH 7.5, hydrolysis temperature of 50 ℃, hydrolyzing time of 6 h.The degree of hydrolysis was 19.25% under the above conditions. The total content of free amino acids of soybean meal was increased to 660% after hydrolysis.

Key words: soybean meal, pretreatment, protease, hydrolysis