Microbial variation and shelf life of chicken breast fillets: A year-long study across two European producers

Despite extensive research on poultry spoilage, variability across batches, seasons, and facilities remains poorly resolved, limiting evaluation of microbiological data for adaptive, data-driven shelf-life determination. This study examined whether initial microbial status, growth dynamics, microbiota composition, and sensory changes varied systematically over one year in modified atmosphere-packed (MAP) chicken breast fillets from two European producers using different gas compositions (Producer A, Norway; Producer B, Portugal). Fillets were analysed after production and during storage at 4 °C or under a 4 to 8 °C temperature shift. Initial total viable counts (TVC) were lower in fillets from Producer A than B, but both producers showed approximately 2-log variation between batches. Maximum growth rates were similar, but Producer B showed shorter model-derived lag times and reached 7 log₁₀ CFU/g earlier. Within each producer, model-based time to 7 log₁₀ CFU/g tracked most strongly with the model-derived lag parameter, whereas initial aerobic TVC showed limited association. During late storage, microbiota communities converged towards distinct spoilage profiles in products from the two producers, and these profiles were largely stable across production days (A: Lactobacillales, Hafnia-Obesumbacterium; B: Brochothrix, Yersiniaceae). Sensory deterioration correlated with TVC and was accelerated but not qualitatively altered by elevated temperature. Overall, initial aerobic TVC was not a reliable predictor of batch-specific shelf life under the MAP conditions studied. Instead, early follow-up measurements after a few days of storage may be needed to capture spoilage-community development and infer batch-specific early growth dynamics, although such indicators require further validation before practical implementation.