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Growth potential of Listeria monocytogenes in ready‐to‐eat Feta cheese‐based sauce stored at 4°C

Andritsos, Nikolaos D., Kallitsis, Theodoros, Roukas, Dimokritos
Journal of food safety 2019 v.39 no.2 pp. e12599
Listeria monocytogenes, bacteria, detection limit, food pathogens, food safety, microbiological quality, pH, ready-to-eat foods, refrigeration, shelf life, sodium chloride, sorbic acid, storage temperature, water activity
Listeria monocytogenes is now a well‐known foodborne pathogen of particular importance in ready‐to‐eat (RTE) refrigerated foods given the psychrotrophic character and ubiquitous nature of the bacterium. The objective of the current research was to assess the growth potential of L. monocytogenes in RTE cheese‐based (Feta) sauce. For this to occur, samples of Feta cheese‐based sauce (ca. 1% NaCl, pH = 4.6, 900 ppm sorbic acid) were artificially contaminated with a mixture of two L. monocytogenes strains and were stored aerobically at 4°C for 30 days. Growth potential (δ) of L. monocytogenes in Feta cheese‐based sauce was calculated at −1.2 log CFU/g for the 30‐day shelf‐life (i.e., δ < 0.5 log CFU/g). Findings of this study indicate that Feta cheese‐based sauce containing 900 ppm of sorbic acid as preservative is unable to support the growth of L. monocytogenes, thus the food safety criterion for pathogen enumeration not exceeding the limit of 100 CFU/g should apply during the shelf‐life of the product, as stated by Commission Regulation (EC) No. 2073/2005. PRACTICAL APPLICATIONS: Contamination of acidic cheese‐based spreadable products, with pH ≤ 4.6 and/or water activity (i.e., Aw) > 0.94, with different bacterial species during the manufacturing process, could limit considerably the shelf‐life of these RTE products. Moreover, among other possible contaminants, the ubiquitous psychrotrophic pathogen L. monocytogenes may pose a serious threat for the microbiological safety of such products, like a Feta cheese‐based sauce with the aforementioned characteristics. Challenge testing for assessing the risk from L. monocytogenes presence during shelf‐life of this product is, therefore, deemed necessary and can provide us with useful information regarding possible pathogen containment due to product's composition and characteristics. Conclusively, even if the Feta cheese‐based sauce described in this study is contaminated with low numbers of L. monocytogenes at levels below the limit of detection (i.e., absence in 25 g), then the organism will not exceed 100 CFU/g by the end of product's shelf‐life.