One measure is prevention of growth through time/temperature control or formulation control. Intrinsic characteristics of a food (e.g., pH, aw) can be leveraged in the product development process to build in effective growth controls. Prevention of growth is essential; Listeria can grow at refrigerated temperatures, which defeats one of the traditional food safety measures. However, the organism is killed by normal food pasteurization and cooking processes, and is typically sensitive to most sanitizers when used at recommended rates and as long as it is not shielded within biofilms. Still, contamination may occur after the cooking process in the processing environment, at retail locations, and in the home. For example, post-pasteurization contamination of food products can occur when the organism is dispersed via an aerosol.
The other essential part of effective control is prevention of contamination of the food through all aspects of the food handling process. This starts with preventing entry of the organism by controlling incoming contamination that can originate with employees, equipment, ingredients, and packaging. Movement of people, equipment, materials, etc., must be monitored, controlled, and restricted as appropriate. Preventing growth in the food handling areas relies on the removal of growth nutrients, including water and soil. Keep areas as dry as possible, keep temperatures low, and have sound sanitation practices. Appropriate sanitation programs include the following considerations.
- Match the cleaner to the nature of the soil;
- Match the cleaner to the water properties;
- Optimize solution compatibility with the surface;
- Ensure the cleaner is appropriate for the method of application;
- Use products that meet environmental guidelines;
- Follow sanitation standard operating practices; and
- Seek guidance from sanitation providers.
- Use EPA-registered products that have a claim against Listeria monocytogenes on the label; and
- Follow the manufacturer’s labeled instructions.
In addition, knowledge of potential harborage sites is important, as contamination is more likely to occur when the organism has become established in a niche where it may be able to evade control measures. Good sanitary equipment design and proper maintenance, in combination with regular, effective, and thorough sanitation, can help eliminate Listeria from niches. Targeting sanitation to the areas where Listeria can be harbored is essential. Food processing plant surveys have found Listeria in the following locations: floors, drains, coolers, cleaning tools, product and/or equipment wash areas, food contact surfaces, condensate, walls and ceilings, and compressed air.
Since it’s essential to detect and manage harborage sites with thorough and frequent sanitizing to control Listeria, a program should include daily sanitation of floors and drains and adequate attention to less frequently cleaned areas such as HVAC systems, walls, coolers, and freezers. Also, damaged equipment, cracks, crevices, and hollow areas must be part of sanitation and inspection schedules. It is essential to avoid creation of aerosols during cleaning, especially of floors and drains, to avoid spread of contamination.
Finally, controlling Listeria also means considering the roles of various transmission routes. The same vectors that can bring Listeria into a facility also need to be controlled once they are inside. These include employees, forklifts, cleaning tools, pests, water, air, etc.
3. Validate the effectiveness of controls. Any control measure implemented with the intent of managing Listeria needs to be chosen carefully and shown to be effective. This is the crux of validation and involves the act of collecting and evaluating scientific and technical information to determine that the control measure, when properly implemented, will achieve the intended result.
For Listeria control, this can come from a variety of sources such as scientific support, including published studies or references; advice from experts including food safety personnel, academics, consultants; and/or in-plant expertise gained from extensive experience. These resources can help assess whether the considered control is theoretically sound. But, the validation process needs to go a step beyond these scientific principles or advice, and must extend to studies demonstrating that the control can be implemented at the site per the plan to achieve the intended results. Evidence must show that the control can be effectively implemented as designed.