Mutation of Rhizopus oryzae IFO 4716 to Give High Glycerol and Low Carbamide in Mirin-Making

Abstract

In order to improve the quality of mirin made with Rhizopus oryzae IFO 4716, a mutant, having high glycerol and low carbamide productivities, was induced by using the ultraviolet irradiation. In the first step of mutation, the screening was made for mutants from Rhizopus oryzae IFO 4716 (parental strain) with high glycerol accumulation, and a mutant (strain HG-1) that accumulated about 1.9 times (>11% of koji wet weight) the glycerol contained in the parental strain was obtained. In a second step, the mutation was induced to the mutant (HG-1) to have low carbamide productivity. Finally, a mutant (strain LC) was obtained that accumulated carbmide less than 4% carbamide comparing with the parental strain in koji. The mirin prepared with R. oryzae LC contained more than 1.0% glycerol and 1.2 ppm carbamide.