Reduction of Escherichia coli O157:H7 populations in soy sauce, a fermented seasoning

Abstract

We studied five Escherichia coli O157:H7 strains in soy sauce which was incubated at 4, 18, or 30°C after inoculation. The cell numbers of E. coli O157:H7 decreased to an undetectable level (<20 CFU/ml) within 9 days in all the soy sauce samples at 30°C, but did not decrease in the 0.1 M phosphate-buffered saline (pH 7.0) control solution under the same conditions. Soy sauce reduced the cell numbers of bacteria at 18°C to a lesser extent than at 30°C, but to a greater extent than at 4°C. Components of soy sauce such as 10% or 16% NaCl, 5% ethanol, lactic acid, or acetic acid at pH 4.5, sodium benzoate (0.6 g/kg), or p-hydroxybenznic acid n-butyl ester (0.05 g/liter) caused a reduction of the E. coli O157:H7 population at 30°C, and the anti-E. coli O157:H7 effect of each component was less than that of soy sauce. The fate of E. coli O157:H7 cells in a buffered solution containing various components of soy sauce resembled that in soy sauce at 30°C, which demonstrated the importance of the combination of the soy sauce components for its anti-E. coli O157:H7 action.