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


P. Van Netten Merck KaGa, Frankfurterstrasse 250, PH20, 64271 Darmstadt, Germany.


Lactic acid decontamination (LAD) may adapt pathogens to lactic acid. Such organisms may have an increased resistance to acid and can contaminate meat after LAD. The survival and growth of acid adapted Campylobacter jejuni, Salmonella typhimurium. Escherichia coli O157 : H7 and Staphylococcus aureus inoculated on skin surface of still warm pork belly cuts 2 h after LAD was examined during chilled (4 °C) storage and refrigeration abuse equivalent to 12·5 °C. Lactic acid decontamination included dipping in 1, 2 or 5% lactic acid solutions at 55 °C for 120 s. Lactic acid decontamination brought sharp reductions in meat surface pH, but these recovered with time after LAD at approximately 1–1·5 pH units below that of water-treated controls. A sharp decrease in the number of cfu of pathogens occurred on chilled 2–5% lactic acid treated pork belly cuts when the skin surface was less than pH 4·8–5·2. The reductions ranged from 0·1–0·3 log10 cfu cm−2 for E. coli O157 : H7 to over 1·7–2·4 log10 cfu cm−2 for Camp. jejuni, respectively. Increase in storage temperature from 4 to 12·5 °C reduced delayed decrease in numbers of all pathogens except Camp. jejuni by a factor of two. Deaths in Camp. jejuni at 12·5 °C slightly exceeded those at 4 °C. After the initial sharp decline, the number of cfu of mesophilic pathogens decreased gradually at a rate similar to that on water-treated controls. Growth of all mesophilic pathogens except Camp. jejuni on 2–5% LAD meat occurred during storage at 12·5 °C when the meat surface pH exceeded 4·8–5·2, and was slower than on water-treated controls. Low temperature and acid-adapted E. coli O157 : H7, Salm. typhimurium and Staph. aureus, and acid adapted Camp. jejuni that contaminate skin surface after hot 2–5% LAD, did not cause an increased health hazard, although microbiota and intrinsic parameters (lactic acid content, pH) were created that could advantage their survival and growth.