When detecting Salmonella spp and Listeria monocytogenes in food production, it is essential to consider the environments in which these pathogens thrive. For example, Salmonella spp tends to exist in dry environments such as flour, bakery products, biscuits, chocolate, herbs, spices, milk powder, and cheese powder. On the other hand, Listeria monocytogenes prefers wet and cold environments and can spread through regular cleaning, especially in refrigerated areas that are cleaned every 8-12 hours. In contrast, dry milk plants may only be wet cleaned once a month or every two months, and dry cleaning is less effective than wet cleaning.
Listeria monocytogenes and Salmonella spp thrive in certain conditions, which include temperature, moisture, pH levels, oxygen levels, and nutrient availability. Both bacteria require nutrients to grow and reproduce, particularly in protein-rich foods. However, there are some differences in the conditions under which Listeria monocytogenes and Salmonella spp thrive. For example, Listeria monocytogenes can grow at refrigeration temperatures, prefers oxygen-rich environments, and has a slightly acidic to neutral pH preference. Salmonella spp, conversely, can grow in a wide range of temperatures, prefers a slightly acidic to neutral pH, and can thrive in both oxygen-rich and oxygen-poor environments. Check out more detailed comparison below.
When checking for Salmonella spp and Listeria monocytogenes in minimally processed factories, you should sample them in similar places. But, again, the focus should be on understanding the risk of cross-contamination of the factory environment and equipment onto the product. According to food safety regulations, the four-zone concept should be used to assess the risk of contamination:
Sampling techniques for detecting Salmonella spp and Listeria monocytogenes depend on specific environments where these pathogens thrive and the zones within the production facility. Here are some commonly used sampling techniques:
The sampling procedure should include Zone 1, Zone 2, and Zone 3 to minimize contamination risks. For example, in Zone 1, the highest level of hygiene and cleanliness is required as this is where the food comes into direct contact with equipment and machinery. Therefore, sampling techniques in this zone may include swabbing surfaces and equipment and environmental testing of air and water samples.
In Zone 2, which includes non-product contact surfaces, swabbing and environmental testing may also be used. However, because the risk of contamination is lower in this zone, sampling techniques may not need to be as rigorous as in Zone 1.
In Zone 3, which includes the outside environment, the risk of contamination is even lower. Sampling techniques in this zone may include testing of surface swabs and water samples but may not need to be as frequent as in Zones 1 and 2.
Finally, in Zone 4, the personnel zone, sampling techniques may include testing hands, clothing, and personal protective equipment (PPE) worn by workers in the processing area. However, the controlling measures in this zone are more related to hygiene control.
Read also: Rapid Testing Methods For Salmonella Monitoring In Food Production
Overall, sampling techniques in each zone aim to identify potential sources of contamination and assess the risk of contamination of food products. Therefore, sampling techniques must be tailored to each zone to provide accurate and meaningful results.