Postprocessing antimicrobial treatments to control Listeria monocytogenes in commercial vacuum-packaged bologna and ham stored at 10 degrees C.

The antilisterial effect of chemical dipping solutions on commercial bologna and ham slices, inoculated (3 to 4 log CFU/ cm2) after processing, was evaluated during storage in vacuum packages at 10 degrees C. Samples were inoculated with a 10-strain composite of Listeria monocytogenes and subsequently immersed (25+/-2 degrees C) for 2 min in 2.5% acetic acid (AA), 2.5% lactic acid (LA), 5% potassium benzoate (PB), or 0.5% Nisaplin (commercial form of nisin, equivalent to 5,000 IU/ml of nisin) solutions, either singly or sequentially (Nisaplin plus AA, Nisaplin plus LA, or Nisaplin plus PB), and then vacuum packaged and stored at 10 degrees C for 48 days. In addition to microbiological analysis, sensory evaluations were performed on uninoculated samples treated with AA, LA, or PB. Initial reductions (day 0) of the pathogen, compared with the controls, on bologna and ham samples treated with AA, LA, or PB ranged from 0.4 to 0.7 log CFU/cm2. Higher (P < 0.05) initial reductions (2.4 to 2.9 log CFU/cm2) were obtained for samples treated with Nisaplin alone and when followed by AA, LA, or PB. L. monocytogenes populations on control bologna and ham samples increased from 3.4 log CFU/cm2 (day 0) to 7.4 and 7.8 log CFU/ cm2, respectively, in 8 days at 10 degrees C. Listericidal effects were observed for all treatments tested, except for Nisaplin applied on its own, during storage at 10 degrees C. The sequential treatment of Nisaplin plus LA reduced L. monocytogenes to undetectable levels in both products at the end of storage. The sequential treatments were also found to inhibit growth of spoilage microorganisms. Sensory evaluations indicated that dipping (2 min) of ham samples in AA (2.5%), LA (2.5%), or PB (5%) led to lower sensory scores. However, since results of this study indicated that these treatments caused extensive listericidal effects, there is possibly a potential to reduce the levels of chemicals applied and still achieve adequate antilisterial activity without major negative effects on product quality.