Fate of low temperature and acid-adapted Yersinia enterocolitica and Listeria monocytogenes that contaminate lactic acid decontaminated meat during chill storage.

Abstract

Pathogens found in the environment of abattoirs may become adapted to lactic acid used to decontaminate meat. Such organisms are more acid tolerant than non-adapted parents and can contaminate meat after lactic acid decontamination (LAD). The fate of acid-adapted Yersinia enterocolitica and Listeria monocytogenes, inoculated on skin surface of pork bellies 2 h after LAD, was examined during chilled storage. LAD included dipping in 1%, 2% or 5% lactic acid solutions at 55 degrees C for 120 s. LAD brought about sharp reductions in meat surface pH, but these recovered with time after LAD at approximately equal to 1-1.5 pH units below that of water-treated controls. Growth permitting pH at 4.8-5.2 was reached after 1% LAD in less than 0.5 d (pH 4.8-5.0), 2% LAD within 1.5 d (pH 4.9-5.1) and after 5% LAD (pH 5.0-5.2) within 4 d. During the lag on 2% LAD meat Y. enterocolitica counts decreased by 0.9 log10 cfu per cm2 and on 5% LAD the reduction was more than 1.4 log10 cfu per cm2. The reductions in L. monocytogenes were about a third of those in Y. enterocolitica. On 1% LAD the counts of both pathogens did not decrease significantly. The generation times of Y. enterocolitica and L. monocytogenes on 2-5% LAD meats were by up to twofold longer than on water-treated controls and on 1% LAD-treated meat they were similar to those on water-treated controls. Low temperature and acid-adapted L. monocytogenes and Y. enterocolitica that contaminate skin surface after hot 2-5% LAD did not cause an increased health hazard, although the number of Gram-negative spoilage organisms were drastically reduced by hot 2-5% LAD and intrinsic (lactic acid content, pH) conditions were created that may benefit the survival and the growth of acid-adapted organisms.