Abstract: Liquid whole duck egg was hydrolyzed by a special-purpose commercial multi-enzyme complex for the hydrolysis of animal proteins and then used to make duck egg sauce with the additions of soybean powder and wheat flour by koji fermentation. Mixed cultures containing Aspergillus oryzae and Aspergillus niger were employed for koji making. The koji-making conditions were optimized using orthogonal array design and neutral protease activity was measured during the process. The optimal koji-making conditions were determined to be: 30% (m/m) duck egg hydrolysate, 3:1 Aspergillus oryzae to Aspergillus niger ratio, and cultivation at 30 ℃ for 48 h. Under these conditions, the protease activity reached 1465.81 U/g dry material.

Key words: Aspergillus oryzae, Aspergillus niger, double strains, koji making, protease activity