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

Abstract

UI S I N 'T VE L D. 1997. 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°C for 120 s. LAD brought about sharp reductions in meat surface pH, but these recovered with time after LAD at ¼1-1·5 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 log 10 cfu per cm 2 and on 5% LAD the reduction was more than 1·4 log 10 cfu per cm 2 . 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.

The survival and growth of acid-adapted mesophilic pathogens that contaminate meat after lactic acid decontamination

“…Pork skin surfaces from cuts of pork belly (about 300 cm 2 ) were inoculated 2 h after water treatment or LAD as described by Van Netten et al (1997). The skin surface pH at inoculation on water-treated controls, 1, 2 and 5% LAD meat was 6·9 2 0·2, 5·1 2 0·2, 4·7 2 0·2 and 4·4 2 0·2, respectively.…”

“…For each experiment, three tests were done ; in each test, the pork skin surface of each pork belly cut was sampled and homogenized as described by Van Netten et al (1997). Sampling of a pork belly cut occurred immediately after inoculation and where appropriate, after 1, 2, 4, 8 and 14 days of storage at 4°C and after 0·5, 1, 2, 3, 4 and 5 days of storage at 12·5°C.…”

“…The pH of skin surfaces was determined as described by Van Netten et al (1997). pH was measured both on water-and LAD-treated pork belly cuts immediately after water treatment and LAD, at the time of inoculation, and after refrigerated storage at 12·5°C for 0·5, 1, 2, 3, 4 and 5 d.…”

“…Temperatures on skin surface of pork belly cuts before and immediately after dipping in decontamination solutions were done as described by Van Netten et al (1997).…”

“…aureus which contaminate pork skin after dipping still warm pork bellies in 1, 2 and 5% lactic acid solutions at 55°C for 120 s. The skin surface of pork bellies was chosen as a model because its buffering capacity is greater than that of other carcass meat surfaces (Bendall 1978). In a previous study, the psychrotrophic pathogens Listeria monocytogenes and Yersinia enterocolitica which contaminate meat after 1-5% LAD (Van Netten et al 1997), was reported.…”