Cheese contamination has hit the headlines in recent weeks after Austrian authorities linked seven listeriosis deaths to Prolactal cheese. In light of this news, food safety experts explain how risk of contamination from Listeria monocytogenes can be minimized in cheese processing.
The main sources of Listeria monocytogenes (LM) contamination are raw materials, processing equipment and environment, and the handling and hygiene practices of workers. Recent surveys have found that processing equipment like holding tanks, storage coolers, table tops, and conveyor systems are all vulnerable to contamination as well as environmental sites such as drains, floors, and storage areas.
LM can form biofilms and be spread from processing equipment and sites to end products through the ventilation system, from dripping and splashing when cleaning with high powered hoses, and by workers themselves. Poor personal hygiene has been identified as one of the most common human errors leading to illness outbreaks.
Prevention steps: Good manufacturing practices (GMP) and good hygiene practices (GHP) should form the basis to prevent contamination of cheese and in general food products from pathogens. Employees should be well trained to understand food safety risks and implement good hygiene practices such as regular hand washing and use of gloves and utensils instead of bare hands. Good cleaning and disinfection routines, especially on surfaces in contact with end products, will also help minimize risk.
Another important factor is plant layout and design, because Listeria monocytogenes can adhere to a wide range of materials and can establish persistent contamination niches in food processing areas. In order to prevent colonization of the processing environment by LM, plant layout and equipment should be designed to be more hygienic, such as without edges, crevices and dead spaces to facilitate good working routines and to ensure an effective sanitation process.
Control strategies: As well as thinking about prevention strategies, food companies must also consider control of LM contamination. Pasteurization is one of the most obvious strategies as this destroys all bacterial pathogens common in raw milk but it is not an option open to makers of un-pasteurized cheese.
Other strategies are to use combined effects of low water activity, low pH and the competition with the starter culture constitutes hurdles that prevent the survival and growth LM in fermented dairy products such as cheeses.