Butter is a complex matrix characterized by a high fat content. Existing publications on the behavior of Listeria monocytogenes in this type of food reported contrasted results. This study was performed to provide further information and data about raw milk butter's ability to support survival or growth of L. monocytogenes. Durability tests were performed on naturally contaminated samples of raw milk butter with various physico-chemical characteristics. At the end of shelf life, no growth of L. monocytogenes was observed in the studied butters, regardless of their physico-chemical characteristics (pH, a w , water dispersion index and salt concentration) and the initial level of contamination. The number of positive samples and the colony counts of L. monocytogenes were even decreased at the end of the storage period.

Description of the subject. According to Regulation (EC) No 2073/2005, Escherichia coli must be enumerated in raw milk butter before sales. Hygiene of batches is acceptable when a maximum of two samples out of five have levels of E. coli between 10 and 100 cfu·g-1. E. coli is still a threat to the safety of raw milk butter. Objectives. This study aimed to identify sources of E. coli in six farms facing recurrent contaminations in butter. Method. Farms were visited three times between March and May 2021. Surface samples and dairy products samples were collected throughout the process for E. coli enumeration and assessment of potential correlations between equipment contamination and hygienic quality of food products. Results. Two major sources of contamination were identified: the lack of efficacy of cleaning and disinfection practices on milk pipelines, junctions and cream separators, and absence of milk cooling in case of time-lapse of more than 2 h between milking and skimming. The use of lactic acid starters could be a helpful way to control E. coli during cream maturation, in association to adequate good manufacturing practices. Conclusions. Levels of E. coli in the considered raw milk butter batches were really high. A new decision tree is proposed that could help manufacturers and food controllers to improve hygienic quality of raw milk butter.