Growth Potential Assessment of Listeria in Milk Fat Products by Challenge Testing

Abstract

Milk fat products (MFP), including butter and low-fat dairy spreads, are a specific type of ready-to-eat food known as water-in-fat emulsions, in which the behavior of microbial foodborne pathogens such as Listeria monocytogenes is not clearly known. This study investigated the growth and survival of L. monocytogenes, and of Listeria innocua as a surrogate for L. monocytogenes, in these foods using challenge testing. Three commercial MFPs with various fat contents (butter, half butter and low-fat dairy spread) and two samples of traditional churned butter with various water droplet sizes were artificially contaminated with Listeria. Total mesophilic microflora including lactic acid bacteria, pH and Listeria were monitored throughout the shelf life. The growth potential of Listeria was calculated in the course of the shelf life and remains below the limit value of 0.5 log cfu/g during the whole shelf life in any of the butter. However, the concentration of Listeria remained stable during the shelf life in the tested MFPs (commercial and churned) except in the commercial low-fat dairy spread in which Listeria decreased gradually. PRACTICAL APPLICATIONSEuropean Union regulation No. 2073/2005 lays down the microbiological limit criteria for Listeria monocytogenes in ready-to-eat foods (RTE). According to this regulation, each RTE food has to be classified, with scientific justification, as able or unable to support the growth of L. monocytogenes during the shelf life. This challenge-test study on milk fat products (MFPs) provided some useful data needed to assess the behavior of Listeria in these particular RTE food products. This study showed that while MFPs do not promote growth, they do support Listeria survival. Water droplet size seems to be a key parameter in preventing the growth of both microflora and Listeria. The study also showed that, in order to determine whether a given MFP supports Listeria growth or not, it is crucial to investigate the impact of the variations in physico-chemical and microbiological parameters of each butter-making process used by companies.

Assessment of growth and survival of Listeria monocytogenes in raw milk butter by durability tests

“…The results relative to the growth of L. monocytogenes in butter were in accordance with those reported by Michelon et al (2016) who observed no growth of the pathogen in the tested samples of churned butters and commercial milk fat products (pH < 5.80). The levels of the bacterium remained however stable during shelf life.…”

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

“…Several recent studies have focused on the growth potential of L. monocytogenes in different RTE food products (Awaiwanont, Smulders, & Paulsen, 2015;Coroneo et al, 2016;Dalzini et al, 2014;Grassi, Nucera, Lomonaco, & Civera, 2013;Jesus et al, 2016;Lahou & Uyttendaele, 2017;Michellon et al, 2016;Sahu, Kim, Ferguson, Zink, & Datta, 2017;Sant'Ana, Barbosa, Destro, Landgraf, & Franco, 2012;Skalina & Nikolajeva, 2010;Spanu et al, 2012;Uyttendaele et al, 2009). These studies intended the classification of foods in the appropriate food category specified in Reg.…”

Overview of the local production process of raw milk butter in Wallonia (Belgium)

“…That allows having smaller moisture droplets, which is important for the keeping quality of butter as it limits the growth of microorganisms (Michelon et al . ).…”

“…In literature, slightly overworking butter is preferred to underworking and increased speed preferred to working at slow speed (Walstra et al 2006). That allows having smaller moisture droplets, which is important for the keeping quality of butter as it limits the growth of microorganisms (Michelon et al 2016).…”