Abstract: In order to maximize protease activity in seed koji, the cooking of raw materials in the production of soy sauce, which was achieved by high-temperature instant cooking combined with low salt solid-state fermentation in this study, was optimized by single factor and orthogonal array design methods with respect to the effects of temperature, time and pressure. Meanwhile, amino nitrogen content in soy sauce mash at different stages of fermentation was determined. Results indicated that the optimal cooking parameters for raw materials of soy sauce were 4 min cooking at 115 ℃ and 0.15 MPa, resulting in the highest protease activity of 3545 U/g, an amino nitrogen content in original soy sauce of 1.078 g/100 mL, and a utilization rate of raw materials of 89%. In practical applications, the optimal process can not only enhance the utilization rate of raw materials and product quality and but decrease manufacturing cost and increase economic profits as well.

Key words: raw materails of soy sauce, cooking process, optimization, protease activity, utilization rate of raw materials