Effect of redox potential on Bacillus subtilis and Bacillus licheniformis in broth and in pasteurized sausage mixtures.

Bacillus licheniformis (a facultatively anaerobe) and B. subtilis (aerobic) may cause spoilage in certain meat products pasteurized in hermetically sealed containers if these are stored with inadequate refrigeration. After having optimized a method for determination of the redox potential in sausage mixtures, we investigated the contribution of low redox potential (Eh) and anaerobiosis to the inhibition of these bacilli. With the Eh values encountered in pasteurized meat products there was no effect of the redox potential on growth of B. licheniformis, either in model broths or in mildly heated bologna-type sausage mixtures. When cultured in a model broth with head space, B. subtilis grew to about 10(7)/ml and was little affected by the initial Eh value (range between +250 and -150 mV) and the initial dissolved oxygen concentration. During exponential growth of this bacterium in the absence of oxygen, the Eh value increased by about 180 mV. In sausage mixture with air inclusions, B. subtilis attained slightly higher cell densities than in mixtures protected against air uptake but it was subsequently overgrown by facultative anaerobic bacilli. We conclude that knowledge of the Eh value of a meat product does not permit a prediction of the growth potential of bacilli in pasteurized meat products, and that a sufficient heat treatment and proper refrigeration are essential to control these bacteria.