Control of Listeria monocytogenes in further processed meat and poultry using organic acid post-cook dips
Johnson, Jennifer L.
Most major outbreaks attributed to Listeria monocytogenes (LM) involve post-processing contamination of turkey and ham deli slices, and frankfurters. This study evaluated the antilisterial effects of organic acids applied as post-cook dips to turkey and ham deli slices and beef frankfurters. Two trials were conducted to analyze LM levels. Efficacy was determined by prolongation of the lag phase and overall LM levels at the end of storage. Treatments included sodium lactate (SL; 3.6%), potassium lactate (PL; 3.6%), sodium citrate (SC; 0.75%), a combination of SL and sodium diacetate (SDA; 0.25%), and a combination of SL/PL/SDA. Products were formulated with 1.5% sodium chloride and 0.45% sodium tripolyphosphate. Ham deli loaves and beef frankfurters were also formulated with 156 ppm and 6.25% sodium nitrite, respectively. Products were surface inoculated with 104-105 log CFU/mL of streptomycin resistant (1,500 ¥ìg/mL) LM strain Scott A before immersion treatment. Positive and negative controls were immersed in sterile water. Products were stored in Whirlpak™ bags under refrigerated temperatures (~4°C) for sampling at 0, 7, 14, 21, 28, 42, and 56 d. The SL/SDA combination applied to turkey extended the lag phase until d21. When applied to ham, the lag phase extended through d14. For both products, LM concentrations rose less than one log (0.7 log CFU/g) throughout the 56 d storage period. The SL/PL/SDA applied to turkey extended the lag phase throughout d 42 with decreasing LM concentrations after d 21. An overall decrease (0.1 log CFU/g) was noted by 56 d. When applied to ham, treatment with a SL and both combination treatments extended the lag phase through d 14. Lag phase in the inoculated control lasted until d 7. Single lactic acid treatments and the SL/SDA combination treatment applied to frankfurters extended the lag phase throughout 28 d post-processing. Lag phase was also extended throughout d 28 for control frankfurters. Treatment with SL/PL/SDA extended the lag phase throughout 21 d. The lag phase for the inoculated control persisted until d 28. Overall growth was limited within the range of 1.0 log CFU/g for all organic acid treatments. Combination organic acid dipping solutions prolonged the LM lag phase for 2 to 6 weeks on treated turkey deli loaves. Combination dipping solutions and sodium lactate extended the lag phase for an additional week beyond the inoculated control when applied to ham. Single and combination lactic acid treatments prolonged the LM lag phase for 3 to 4 weeks on treated beef frankfurters, but the same results were noted on untreated frankfurters.