Behavior of Listeria monocytogenes during the Shelf-life of Fresh Refrigerated Pesto Sauce, According to Regulation (EU) 2073/2005 and Subsequent Amendments

Aims: Ligurian pesto is one of the most popular condiments for pasta. For microbiological purposes, refrigerated pesto sauce is a great matter for concern, as it can be contaminated by microorganisms originating from both raw materials and manufacturing processes. Listeria monocytogenes is a potential microbiological hazards for this product. The regulatory approach (EU) No. 2073/2005, with subsequent amendments and integrations, takes into consideration the concentration of this pathogen in foods and its growing ability. This study is aimed to assess whether fresh pesto sauce can be included among the Ready-To-Eat (RTE) foods that do not support the growth of L. monocytogenes.

Place and Duration of Study: Quality, Safety and Pre-Industrialization Area, Stazione Sperimentale delle Conserve Alimentari- SSICA, Parma, Italy. Study carried out between October 2021 and June 2023.

Methodology: A screening on 48 different types of commercially available fresh pesto sauces was carried out, evaluating physiochemical parameters (pH and aw). For three different pesto sauces with physical-chemical characteristics suitable for L. monocytogenes growth, microbiological analyses were carried out on both non-inoculated and inoculated samples. The inoculum was made using a mixture of L. monocytogenes, to evaluate its behaviour during the pesto shelf-life.

Results: A relevant presence of commercially available pesto sauces supporting the pathogen growth was found. The study highlighted the inability of the inoculated L. monocytogenes to grow in the tested pesto sauces at 7°C and 10°C during the labelled shelf-life (that varied from 9 to 33 days).

Conclusion: The results obtained from the study can be helpful to the food companies producing pesto sauces, to predict the behaviour of the microorganism and to correctly classify the product, in accordance with the reference regulation (EU) No. 2073/2005 and its subsequent amendments.