The objective of this study was to evaluate the effect of a plant extract blend containing rosemary and citrus extract on controlling the growth of Listeria monocytogenes in highly extended sliced cook-in ham during refrigerated storage at 7°C.

The experiment comprised 2 treatments, control (no plant extract addition) and 0.4% of rosemary-citrus extract blend (Cleanatis M1, Naturex). This study was conducted using a standard ham formulation yielding an end product weighing 170% of the raw material used, in this case pork leg meat cuts. The different ham muscles obtained from the pork leg were injected with a brine solution containing water, sodium chloride, phosphates, sodium nitrite, sodium erythorbate, hydrolyzed corn syroup 40DE, monosodium glutamate, carrageenan and aromas. Each lot included one batch of samples tumbled (7 cycles/min) under vacuum, at controlled temperature between 0 and 4°C for 9 h and stuffed in polyamide impermeable casings (60 mm diameter to form cooked ham pieces with approximately 1.2 kg each. The ham pieces were cooked in water tanks (80°C) at a commercial pilot plant to reach 72°C. Cooking time was approximately 1 h and 30 min. After the cooking stage, samples were cooled with ice and refrigerated at 0 to 4°C overnight The ham pieces were transported to CTC/ITAL on ice box and immediately sliced for microbiological analysis at arrival. The ham slices (2 to 3 mm) were inoculated with 0.1 mL of of L. monocytogenes ATCC7644, to yield approximately 4 log CFU/g. Inoculated samples were vacuum packaged in gas-impermeable pouches and stored at abuse temperature (7°C), very common in Brazilian retail market, for up to 16 d. Bacterial populations were determined following ISO 11290–2:2017 method. Triplicate samples of each treatment were assayed at 0 time and after 2, 4, 6, 8, 10, and 12 d of storage for L. monocytogenes populations. In addition, triplicate inoculated samples were assayed for lactic acid bacteria populations following ISO 15214:1998 method. Data Interactions and main effects were considered significant at P < 0.05. The data were submitted to analysis of variance to evaluate the effect of the treatments, storage time and the treatment × time interaction using Statistica 7.0 (StaSoft Inc). The difference between the mean values was evaluated by Tukey´s test at the 95% confidence level.

During storage, the difference between L. monocytogenes counts in the treatment containing the plant extracts and control was 0.5 log CFU/g. There was a significant effect (P < 0.05) of the interaction treatment versus time on L. monocytogenes growth, the counts remained 0.5 log lower on samples containing the plant extract blend. Lactic acid bacteria counts were below 1.0 Log CFU/g during shelf life for both treatments.

These data suggest that the plant extracts blend can enhance the safety of sliced cook in ham. It is important to evaluate the effect in meat systems without nitrite addition or along with other interventions that inhibit growth, like post packaging pasteurization.