ObjectivesWorld’s largest outbreak of listeriosis in South Africa last year, remind us that Listeria monocytogenes contamination and growth is still of major concern in refrigerated RTE meats. The same time customers demand for clean label food safety solutions. Provian NDV, a fermented vinegar based powder, was developed to provide a clean label solution that inhibits Listeria monocytogenes during long term refrigerated storage. This document describes the effect of chemical derived acetates and Provian NDV, a novel vinegar based product, on the inhibition of Listeria monocytogenes in a cooked meat applicationMaterials and MethodsFive treatments of cured deli-style ham were tested. The pork ham contained 72–74% (w/w) moisture, 1.75 ± 0.1% (w/w) salt, and pH 6.2–6.4, 156 mg/kg sodium nitrite and 547 mg/kg sodium erythorbate. The treatments included a control without antimicrobials and different concentrations of a chemically derived acetates (0.5% and 0.75%) and Provian® NDV (0.5%, 0.65%). Cooked products were surface-inoculated with 3-log10 CFU/g of a cocktail of 5 strains of Listeria monocytogenes from the culture collection of Food research institute, Wisconsin University including serotypes 4b, 1/2a, and 1/2b. All strains were isolated from RTE- cooked meat products. Inoculated slices (100 g/package) were vacuum-packaged and stored at 4°C and 7°C for 8 to 12 wk. Per treatment triplicate samples were assayed by enumerating on modified Oxford Agar. One way ANOVA was used to analyze significance, p < 0.05. Except from the triplicate repeat, this study was conducted twice independently (trial 1, 5 treatments in triplicate and trial 2 including same treatments, also in triplicate.)ResultsControl Ham supported > 1 log increase of L. monocytogenes at 4- and 2-weeks storage at 4 and 7°C, respectively. In contrast, hams supplemented with 0.5 or 0.75% chemical acetates or 0.65% Provian® NDV inhibited the Listeria growth for 12 and 8 wk at 4 and 7°C, respectively. Inhibition of Listeria on ham supplemented with 0.5% Provian®NDV was further affected by pH and moisture. Ham supplemented with 0.5% Provian® NDV in the trial 1 (71.5% moisture, pH 6.2) delayed Listeria for 12 wk storage at 4°C, whereas individual samples of trial 1 (72.9% moisture, pH 6.3) supported growth (> 1 log increase) at 8 wk. Similar trends were observed at 7°C. The images below reflect the results of trial 1 only.ConclusionThis study confirms the efficacy of acetates on the inhibition of Listeria monocytogenes. Next, this study shows that a product based on natural fermented vinegar, Provian NDV, has a comparable growth inhibitive action in a cured ready-to eat ham. This illustrates that most relevant serotypes (4b, 1/2b and 1/2a) of Listeria moncytogenes can be controlled using an ingredient based on natural fermented vinegar.Figure 4.
Sub‐lethal damage ofListeria monocytogenesafter long‐term chilled storage at 4 °C
