Is Butter a Product at Risk Regarding Listeria monocytogenes? - A Review

This review gathers information on the occurrence and survival of Listeria monocytogenes in butter. Whether it is the cattle, the equipment or the barn environment, dairy farms represent a big reservoir of L. monocytogenes. Processing environments can also be a source of contamination. Yet, the level of contamination of butter by the pathogen is low. The growth potential of L. monocytogenes in butter is also reduced due to various factors. Among other parameters, the influence of pH and water droplets size and distribution on the behavior of the pathogen is discussed

La réalisation de tests de provocation et d'études de vieillissement pour évaluer la croissance de Listeria monocytogenes au sein des denrées alimentaires: le cas de produits laitiers fermiers

peer reviewedListeria monocytogenes est la bactérie pathogène responsable de la listériose, une toxi-infection d’origine alimentaire dont le nombre de manifestations n’a cessé d’augmenter depuis une dizaine d’années au sein de l’Union européenne. En 2018, cette toxi-infection s’est traduite par la mort de plus de 15 % des personnes infectées. De nombreux aliments sont susceptibles de permettre la croissance de ce pathogène, ou au minimum sa survie. Parmi les techniques disponibles pour évaluer la croissance de L. monocytogenes au sein d’une denrée alimentaire figurent les tests de provocation et les études de vieillissement. La première méthode consiste en une inoculation de la bactérie au sein ou en surface du produit à étudier, ce dernier étant ensuite conservé jusqu’à sa date limite de consommation. Les niveaux de contaminations initiale et finale permettent alors de calculer un potentiel de croissance et de se prononcer quant aux risques pour la sécurité sanitaire liés à la présence de L. monocytogenes au sein de l’aliment concerné. Les études de vieillissement se basent quant à elles sur une contamination naturelle de la denrée alimentaire par L. monocytogenes. Dans ce cas, le lot contaminé complet doit être conservé jusqu’à la date limite de consommation. La proportion des unités dépassant la limite de 100 ufc/g est alors calculée. Le Laboratoire Qualité et Sécurité des Produits Agroalimentaires de Gembloux Agro-Bio Tech – Université de Liège a fait de l’étude de la croissance de L. monocytogenes au sein des produits laitiers fermiers l’une de ses principales thématiques de recherche

Study of the bacterial flora and the growth of Listeria monocytogenes in raw milk butter

Listeria monocytogenes is a foodborne pathogen for which growth in food depends on the latter's physico-chemical characteristics and the presence of inhibitors such as lactic acid bacteria. To study the growth of Listeria monocytogenes in raw milk butter, challenge test was conducted. Two approaches of butter production were simulated. The first one used cream matured at 4°C while the second one used cream matured at 14°C. Samples of cream and butter were taken at several days for pH and microbiological analyses. Metagenetic analyses were also conducted on all samples. The two batches of butter showed different bacterial profile. The first batch made from refrigerated cream presented a big diversity and was characterized by an abundance of psychotropic bacteria. This batch showed an increase in the level of Listeria monocytogenes during butter storage. The growth potential of Listeria monocytogenes, defined as the difference between the median of the counts at the end and the median of the counts at the beginning of storage, was 1.81 log cfu/g. The second batch made from cream matured at 14°C was characterized by a dominance of Lactococcus. The latter was even more abundant in inoculated samples than in control samples. This batch presented a decrease of Listeria monocytogenes during butter storage with a growth potential of -1.72 log cfu/g. These data suggest that cream maturation is an important factor to the growth of Listeria monocytogenes and lactic acid bacteria especially Lactococcus

Study of the development of Listeria monocytogenes in raw milk butter

Currently, Listeria monocytogenes is considered one of the most important foodborne pathogens. It is often implicated in epidemics of human listeriosis that represents a real health risk, given the high mortality rate (over 25%) of infected persons. Listeria monocytogenes can directly or indirectly contaminate products and the environment, which makes Listeria a worrying pathogen for the dairy industry. The Commission Regulation (EC) 2073/2005 on microbiological criteria for foodstuffs, imposes an absence of this pathogen in 25g of the products able to support the growth of Listeria monocytogenes. This criterion is applicable to products before they leave the immediate control of the food business operator, unless the manufacturer is able to demonstrate, to the satisfaction of the competent authority, that the product will comply with the limit of 100 cfu/g throughout the shelf life. As butter is a product with a wide variation in the production process, more information and data on the growth and survival of Listeria monocytogenes in relation to formulation and butter structure are therefore needed

Inventory of the raw milk butter production in Wallonia (Belgium)

Since the fourteenth century, the marketing of butter, which is considered one of the first dairy products, is done on an international scale. In Belgium, butter production in 2016 increased by 7.7% in comparison with 2015 to reach 87,506 tons. According to the scientific opinion 09/2016 of the Scientific Committee of the Federal Agency for the Safety of the Food Chain, there is a wide variation in the production processes and types of farm butter made from raw milk

Determination of the growth potential of Listeria monocytogenes in various types of Belgian artisanal cheeses by challenge tests

Cheese potentially allowing the growth of Listeria monocytogenes must be free of the pathogen in 25 g before being put on the market, while 100 cfu/g is tolerated when the pathogen is unable to grow. Challenge tests were performed in order to assess the growth potential of L. monocytogenes in at least one batch of 32 Belgian cheese varieties from 32 factories. All varieties were grouped in four categories: unripened acid-curd cheeses, mold-ripened soft cheeses, smear-ripened soft cheeses and ripened semi-hard cheeses. Associated microflora and cheese physicochemical characteristics were also studied. A cocktail of three strains was used to inoculate cheese on the first day of shelf-life, and samples were stored until the end of shelf-life at 7-9 °C. Growth potential was considered as the difference (a) between median contamination at the end and at the beginning of the test or (b) between the highest value at the end of the test and the lowest value at its beginning. L. monocytogenes always decreased in unripened acid-curd cheeses but showed extended growth in 21 out of 25 batches of ripened soft cheese. Contrasting results were obtained for semi-hard cheeses, as important intra- and inter-batch variability was observed. For the latter, the recommended method based on medians to calculate the growth potential led to erroneous food safety considerations, and it should always be advised to focus on absolute levels

Survey on the prevalence of Listeria monocytogenes in Belgian artisanal cheeses

Description of the subject. Cheese is a vector of Listeria monocytogenes. By default, European Commission imposes its absence in cheese before sales, but fixes pH and water activity thresholds below which it cannot grow. Objectives. To study pH and water activity of Belgian cheeses and the prevalence of L. monocytogenes in these products. Method. Salt content, pH and water activity of 134 cheeses were determined. Absence of L. monocytogenes in 25 g of cheese was also checked. Results. Three samples had pH or water activity under threshold values from regulation. Nevertheless, all unripened cheeses were acid in comparison with data from foreign countries. Listeria monocytogenes was isolated from 1.49% of the samples. Conclusions. Belgian artisanal cheeses could allow the growth of L. monocytogenes, and the bacterium was isolated from two samples. Further experiments should be performed to understand the fate of the pathogen in these products