The immediate bactericidal effect of lactic acid on meat-borne pathogens

The kinetics of the bactericidal effect of lactic acid decontamination (LAD) on meat-borne pathogens (Salmonella spp., Campylobacter jejuni and Listeria monocytogenes) was studied in an in-vitro model. The bactericidal effect was greatest on organisms in the lactic acid film that replaced the natural fluid on the meat surface during LAD. A stepwise increase in pH from 2.6 to 3.5 and 4.0 progressively reduced the bactericidal effect of decontamination. For treatment with 2% lactic acid for 30-90 s at 21 degrees C, the immediate death of Salmonella spp. decreased from about 0.5-2 log10 cfu at pH 2.6 to an insignificant level at pH 4.0. The immediate death for Camp. jejuni decreased from 2.6 to > 5.3 at pH 2.6 to 0.3-1.0 at pH 4.0. The decrease in bactericidal effect with increasing pH could, however, be countered by an increase in the temperature from 21 degrees C to 37 degrees C. It is suggested that 2% LAD at 37 degrees C for 30-90 s is suitable for elimination of salmonellas on meat but not for L. monocytogenes. Decontamination with 1% lactic acid at pH 3.0 and 21 degrees C for at least 30 s was effective for Camp. jejuni. Mesophilic Enterobacteriaceae were reliable indicators of the LAD-induced bactericidal effect on Salmonella spp. and Camp. jejuni.