Growth and Biocontrol of Listeria monocytogenes in Greek Anthotyros Whey Cheese without or with a Crude Enterocin A-B-P Extract: Interactive Effects of the Native Spoilage Microbiota during Vacuum-Packed Storage at 4 °C.

Nikoletta Sameli,John Samelis

doi:10.3390/foods11030334

Abstract

Effective biopreservation measures are needed to control the growth of postprocess Listeria monocytogenes contamination in fresh whey cheeses stored under refrigeration. This study assessed growth and biocontrol of inoculated (3 log10 CFU/g) L. monocytogenes in vacuum-packed, fresh (1-day-old) or ‘aged’ (15-day-old) Anthotyros whey cheeses, without or with 5% of a crude enterocin A-B-P extract (CEntE), during storage at 4 °C. Regardless of CEntE addition, the pathogen increased by an average of 2.0 log10 CFU/g in fresh cheeses on day 15. Gram-negative spoilage bacteria also increased by an average of 2.5 log10 CFU/g. However, from day 15 to the sell-by date (days 35–40), L. monocytogenes growth ceased, and progressively, the populations of the pathogen declined in most cheeses. This was due to an unmonitored, batch-dependent natural acidification by spoilage lactic acid bacteria, predominantly Leuconostoc mesenteroides, which reduced the cheese pH to 5.5, and finally to ≤5.0. The pH reductions and associated declines in pathogen viability were greater in the CEntE-treated samples within each batch. L. monocytogenes failed to grow in cheeses previously ‘aged’ in retail for 15 days. Overall, high population levels (>7.5 log10 CFU/g) of psychrotrophic Enterobacteriaceae, particularly Hafnia alvei, were associated with an extended growth and increased survival of L. monocytogenes during storage.

Highlights

Accepted: 21 January 2022Listeria monocytogenes remains a food-borne pathogen of great concern for the dairy industry [1,2]
L. monocytogenes in Greek Anthotyros whey cheeses when the artificial contamination with the pathogen was introduced in 50 g portions of fresh (1-day-old) retail cheese batches before vacuum packaging and storage at 4 ◦ C for up to 40 days
The results revealed the vital importance of an unmonitored whey cheese acidification by native lactic acid bacteria (LAB), predominantly

Summary

Introduction

Accepted: 21 January 2022Listeria monocytogenes remains a food-borne pathogen of great concern for the dairy industry [1,2]. L. monocytogenes and may support its growth during retail distribution and storage [7,8,9,10]. Only RTE cheese products that do not support listerial growth, either a priori based on the pH/aw set value criteria or after research-based challenge testing, can harbor a maximum allowable L. monocytogenes level of 100 CFU/g during retail shelf life [11]. Numerous early to recent challenge studies have shown that fresh whey cheeses are the riskiest soft RTE cheese products with regard to L. monocytogenes outgrowth because of their high pH (>6.0–6.8) and moisture (>60–80%) content that corresponds with water activity values much above the aw 0.94 threshold [12,13,14,15,16,17]. The strict alternative microbiological criterion ‘absence of L. monocytogenes in 25 g’, defined as the ‘zero

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Conclusion