Listeria monocytogenes Survey in Cubed Cooked Ham Packaged in Modified Atmosphere and Bioprotective Effect of Selected Lactic Acid Bacteria

The aim of this work was to study the presence of Listeria monocytogenes, as well as the potential activity of two bioprotective cultures (Lyocarni BOX-74 and Lyocarni BOX-57), versus a mix of three L. monocytogenes strains that were intentionally inoculated in cooked cubed ham, packaged in Modified Atmosphere Packaging and stored at different temperatures. The bioprotective cultures limit L. monocytogenes growth in cubed cooked ham stored either at 4 °C for 60 days and at 4 °C for 20 days and at 8 °C for 40 days. The inhibition at 8 °C is particularly useful for industrial cooked meat products, considering there are often thermal abuse conditions (8 °C) in the supermarkets. Both the starters can eliminate L. monocytogenes risk and maintain the products safe, despite the thermal abuse conditions. In addition, both culture starters grew without producing perceptible sensory variations in the samples, as demonstrated by the panel of the untrained tasters. The bioprotective LAB produced neither off-odours and off-flavours, nor white/viscous patinas, slime, discoloration or browning. Therefore, according to the obtained data, and despite the fact that cooked cubed ham did not show pH ≤ 4.4 or aw ≤ 0.92, or pH ≤ 5.0 and aw ≤ 0.94, as cited in the EC Regulation 2073/2005. It can be scientifically stated that cubes of cooked ham with the addition of bioprotective starters cultures do not constitute a favourable substrate for L. monocytogenes growth. Consequently, these products can easily fall into category 1.3 (ready-to-eat foods that are not favourable to L. monocytogenes growth, other than those for infants and for special medical purposes), in which a maximum concentration of L. monocytogenes of 100 CFU g−1 is allowed.

Characterization and Growth under Different Storage Temperatures of Ropy Slime–Producing Leuconostoc mesenteroides Isolated from Cooked Meat Products

ABSTRACT The presence of lactic acid bacteria can be detrimental when the abundant growth of slime-producing strains (Lactobacillus spp. and Leuconostoc spp.) causes spoilage of meat products. Two strains of lactic acid bacteria were isolated from vacuum-packed cooked hams that had been withdrawn from the market for the so-called ropy slime defect and identified as Leuconostoc mesenteroides. In an attempt to define the behavior of ropy slime–producing bacteria, two strains of L. mesenteroides were incubated in de Man Rogosa Sharpe broth at different storage temperatures and conditions of thermal abuse (4, 12, 20, 30, 37, and 44°C). Both strains showed a lack of growth at 44°C, a good level of development at 30 and 37°C, and evident growth ability at low temperatures, with a long stationary phase. In particular, the bacterial concentration at 4°C was >105 CFU mL−1 after more than 120 days of incubation. This study demonstrates that the refrigeration temperature for cooked meat products does not constitute a hurdle for ropy slime producers and their subsequent ability to spoil. HIGHLIGHTS