Effects of spray volume, type of surface tissue and inoculum level on the survival of Escherichia coli on beef sprayed with 5% lactic acid

Membrane, fat and cut muscle surfaces of beef were inoculated with Escherichia coli at numbers about 4, 1 or −1logcfu/cm2. The inoculated meat was sprayed with water or 5% lactic acid at volumes of 0.5, 0.1 or 0.02ml/cm2. Spraying with water reduced the numbers of E. coli on membrane surfaces by up to 1log unit, but had little effect on the numbers of E. coli on fat or cut muscle surfaces. Spraying with 5% lactic acid reduced the highest numbers of E. coli on membrane surfaces by up to 4log units; but those numbers on fat or cut muscle surfaces were reduced by ≤1.5log unit, and the reductions declined with decreasing volumes of 5% lactic acid. With inocula of 1logcfu/cm2, spraying lactic acid in any volume reduced the numbers of E. coli on membrane or fat surfaces by about 1log unit, and the numbers on cut muscle surfaces by between 0.8 and 0.2log unit. E. coli were detected in enrichment cultures of samples from all surfaces inoculated with E. coli at −1logcfu/cm2 and sprayed with 5% lactic acid at 0.5ml/cm2. The findings indicate that spraying relatively heavily contaminated cuts or trimmings with 5% lactic acid at ≥0.1ml/cm2 can be expected to reduce numbers of E. coli and, presumably, associated pathogens by between 0.5 and 1log unit. However, such a treatment is likely to be at best marginally effective for reduce the numbers of these organisms on lightly contaminated product. ► Beef surfaces inoculated with Escherichia coli were sprayed with 5% lactic acid. ► With large inocula, reductions were greater for E. coli on membrane than on fat or cut muscle surfaces. ► With small inocula, reduction on membrane and fat surfaces were similar and greater than reductions on cut muscle surfaces. ► With very small inocula, E. coli were recovered from all treated surfaces by enrichment. ► 5% Lactic acid will not eliminate E. coli from beef trimmings.