Assessment of the Spoilage Microbiota and the Growth Potential of Listeria monocytogenes in Minced Free-Range Chicken Meat Stored at 4 °C in Vacuum: Comparison with the Spoilage Community of Resultant Retail Modified Atmosphere Packaged Products

Abstract

Although current diet and nutrition trends in developed countries led the poultry industry to shift to alternative breeding/production methods, such as organic and free-range, limited data on the microbiology of alternative compared to conventional poultry meat products exist. Therefore, this study assessed the evolution and composition of the spoilage microbiota and the growth potential of inoculated (3 log cfu/g) Listeria monocytogenes in freshly minced free-range chicken meat stored at 4 °C in vacuum packages (VP; four batches) for 0, 3, 5, 7, and 10 days. Additionally, two VP batches were compared with their resultant retail products stored in modified atmosphere packages (MAP 30:70 CO2/N2) at 4 °C to detect potential differences with the MAP spoilage community described previously. The initial pH of the VP minces was 6.0–6.1, except for one mince, designated VP + AA, which had initial pH 5.8 and was found to contain ‘external’ 1.26% L-lactate and 0.24% acetate associated with a vinegar smell during storage. The rest of the VP batches contained on average 0.75% L-lactate and 0.02% acetate on day 0. After 7 days at 4 °C, L-lactate decreased by at least 3-fold in VP and over 5-fold in VP + AA vs. minor decreases in MAP. Acetate increased 2-fold in all batches. D-lactate (ca. 0.02% on day 0) increased by 4-fold in VP batches only. Lactic acid bacteria (LAB) became the dominant spoilers in all samples. Only VP allowed a delayed 10-fold growth (>5.0 to 6.2 log cfu/g) of pseudomonads from day 7 to day 10 at 4 °C. Compared to VP, VP + AA and MAP retarded growth of LAB, pseudomonads, and enterobacteria by 1–2 log units, at final levels below 6.5, 4.5, and 3.0 log cfu/g, respectively. Enterococci, staphylococci, yeasts, and L. monocytogenes did not grow. Latilactobacillus sakei predominated in all spoiled VP batches (65.8% of 80 meat isolates) followed by Latilactobacillus fuchuensis (9.2%), Leuconostoc carnosum (6.6%), Carnobacterium divergens (6.6%), Latilactobacillus curvatus (5.3%), and Weissella koreensis (2.6%). VP + AA favored Latilactobacillus. Brochothrix thermosphacta was frequent in one VP batch. In conclusion, cold-stored (4 °C), minced, free-range chicken meat spoils more rapidly and offensively under VP than MAP or VP combined with acetate-containing (VP + AA) antimicrobial blends.