Purpose: The purpose of this study was to: (1) determine in pure culture the bactericidal activity of 3% lactic acid and 0.5% levulinic acid plus 0.05% sodium dodecyl sulfate (SDS) on STEC and (2) compare the efficacy of different treatment application methods, including spraying, immersion with pressure by hands and immersion without pressure, to inactivate E. coli O157:H7 on beef trim.
Methods: Lactic acid and levulinic acid and sodium dodecyl sulfate (SDS) were tested individually or in combination at different concentrations at 21°C for their killing effect on different isolates of STEC. Beef (25-35% fat content, cut into 10 x 10 x 7.5-cm portions) was inoculated by immersion with 107-8 CFU E. coli O157:H7/ml for 1 min and mixed by hand with uninoculated beef trim at a ratio of 1:5 for 2 min. The inoculated beef was held in a laminar hood for 20 min before treatment. Treatments were applied by the methods described above.
Results: Applied to pure cultures, 3% lactic acid treatment for 5 min at 21°C reduced E. coli O26:H11, O45:H2, O111:H8, O103:H2, O121, O145:NM, and O157:H7 populations by 2.5, 1.9, 1.0, 2.8, >6.5, 4.3, and >6.7 log CFU/ml, respectively. However, treatment with 0.5% levulinic acid plus 0.05% SDS for <1 min at 21°C reduced all STEC by >6 log/ml reduction to undetectable populations. The spray treatment was least effective in reducing E. coli O157:H7 counts, providing a 0.5 and 1.0 log/CFU/sample reduction, whereas immersion without pressure provided a 1.0 and 1.5 log/CFU/sample reduction, and immersion with pressure provided an additional 0.5 and 1.0 log/CFU/sample reduction.
Significance: Results revealed that an immersion treatment with pressure was the most effective in reducing E. coli O157:H7 counts on contaminated beef trim.