Inhibition of bacillus cereus in doenjang fermented with multiple starters showing inhibitory activity against pathogens

Abstract

Doenjang samples were prepared by inoculation of multiple starters consisting of two Bacillus spp., one yeast, and one fungus. Doenjang A was fermented with Bacillus amyloliquefaciens EMD17, B. amyloliquefa-ciens MJ1-4, Pichia farinosa SY80, and Rhizopus oryzae. Doenjang B and C were fermented with the same yeast and fungus but different Bacillus strains; namely, B. amyloliquefaciens EMD17 and B. subtilis CH3-5 for doenjang B, and B. amyloliquefaciens MJ1-4 and B. subtilis CH3-5 for doenjang C. Doenjang D was fermented with microorganisms present in rice straw (control). The doenjang samples were spiked with B. cereus ATCC14579 at two different levels, 104 CFU/g doenjang (I) and 107 CFU/g doenjang (II). All eight doenjang samples were fermented for 70 days at 25°C. Growth of B. cereus was inhibited in doenjang A, B, and C, with the bacterial cell count after 70 days being less than the initial 104 CFU/g added, whereas B. cereus was not inhibited in doenjang D. Doenjang B showed the strongest inhibitory activity against B. cereus, with a cell count of less than 103 CFU/g after 42 days, even when B. cereus was initially added at 107 CFU/g. Some properties of the doenjang samples, such as pH, TA, and amino-type nitrogen content, were similar to those of doenjang fermented with starters only. The results indicate that carefully selected starters can effectively prevent the growth of B. cereus during doenjang fermentation. ? 2016, The Korean Society for Microbiology and Biotechnology.