UV treated a strain of Aspergillus oryzae traditionally used for production of soy sauce in a famous company located in Guangdong and a mutant with high-activity neutral proteinase was obtained, named YB-1. The amino-nitrogen content and the organoleptic properties of soy sauce were improved by optimization of fermentation technology.The Aspergillus oryzae was induced under different strength of ultraviolet radiation and neutral proteinase activity was used as an index for screening the strains using for fe...