Ultraviolet(UV)and nitrosoguanidine(NTG)were employed to mutate Lactic acid bacteria from fermented soybean for high acid-producing capacity.Acidness of the mutant strain improved30.77% higher than the original strain,and the mutant kept good hereditary stability.Response surface designs were used to explore the effects of incubation temperature time,incubation time and inoculation amount on the strain acid yield.Results showed that the optimal conditions were incubation temperature of 41.72 ℃,inoculation a...