Safeguarding Our Food From Listeria

Safeguarding From Listeria In Ready-to-Eat Foods

Consumers are not aware of the possible dangers of ready-to-eat (RTE) foods. Without proper care and handling of products, dangerous bacteria can become the culprit of illness. Listeria is a bacterium that has had a large impact on the food industry and the products sent to local stores. An emphasis on proper sanitation, packaging, and training are crucial to prevent future outbreaks. A proper procedure to carry out these points can save future anguish for the company and buyers.

What is Listeria?

Microbiologically, Listeria bacteria are categorized as an environmental organism, which means that they occur naturally in the environment. They flourish at temperatures as low as 3°C (37°F) and are resistant to heating and freezing.

Food residues remaining on food contact surfaces become a starting point for the formation of biofilm, which provides harborage for bacterial contamination, including the notorious Listeria species. As a biofilm grows and hardens, it flakes off into subsequent batches of product. This results in contamination of the product.

Non-food contact surfaces and environmental areas may also harbor Listeria if sanitation standard operating procedures (SSOPs) have not been followed correctly. What a facility considers “good manufacturing practices” (cGMPs) may also contribute to contamination problems if they are inadequate or not properly and consistently followed.

Image Source: Center for Disease Control and Prevention


What Can We Do for Listeria Control?

How can the Listeria problem be controlled?  What requires specific attention to succeed in consistently producing safe RTE products? There are four primary areas of focus to control Listeria, which include:

  • sanitation
  • product design / handling / packaging
  • procedures and employee training
  • validation of processes and procedures


Food Processing Sanitation

Processes that keep the product safe are ideal in controlling Listeria. The most basic of these processes is plant sanitation. Equipment should be aggressively scrubbed with appropriate cleaners to prevent the build-up of residue that could lead to the formation of biofilm. Sanitizers should be appropriate to remove the various residues. It is also important to adjust the sanitizers for the chemistry (pH, hardness) of the plant’s water supply for maximum effectiveness. Temperature and contact time of sanitizers are critical factors.

Environmental surfaces deserve careful attention, as potential indirect routes of contamination are abundant. Employee training on sanitation operations, with annual updates, is an effective way to improve.  Validation of the sanitation process is important and should be accomplished by the use of routine swab analyses to demonstrate the effectiveness of the process. An effective swabbing program will detect “positives” for Listeria from time to time. Where weaknesses are found, improvements should be made. This information will keep the sanitation team focused on eliminating the problem.

Effective testing to support sanitation is an effective way to identify and reinforce “best practices” regarding both SSOPs and the sanitizers used, as well as to support the sanitation team’s training.


Product Design, Handling, and Packaging

Finished product quality correlates directly to raw material quality. To ensure optimal effectiveness of facility processing, it is critical to control the microbiological quality of the raw materials. Controlling said quality is accomplished by use of purchase specifications, along with a system of verifying that those specifications are being met. Many successful facilities use a combination of hurdle strategies, preservatives, and thermal or other lethality steps in their processing to obtain optimal product quality control. Salt content, water activity, and pH controls are three hurdles that may be used.

Product preservation may also be achieved using either chemical or natural preservatives. Companies are discovering that certain pairings of preservatives offer greater effectiveness.

The most important processing step is the lethality step. This step must be validated regularly – for every product – to demonstrate the step’s effectiveness. It is essential to set appropriate, routine operational tolerances, as the sole use of critical tolerances fails to permit correction of the process before the end product has failed specifications.

Post-lethality handling of RTE products should be carefully monitored to ensure no contamination occurs. In products such as cold-smoked seafood, where there is no thermal processing, product design is even more critical. Handling, and packaging all compensate for the lack of a “kill step.” [AP5] Vacuum Packing (CVP) and Modified Atmosphere Packing (MAP) are two examples of product packaging that can play a key role in maintaining product quality control.

Validation studies offer a way to confirm that a process produces a safe product. Changes in equipment (including those that result from aging), vendors, product formulation, and packaging are all sufficient reasons to re-validate a process. The net effectiveness of processing, preservative systems, and packaging must be tested. These include challenge studies, shelf-life studies, and other testing to demonstrate control over the entire process.


Employee Training for Food Safety

To implement properly into a facility cGMPs, SSOPs, and a HACCP plan, employees should receive continual training. It is critical to provide training to address proper day-to-day requirements for the safe operation of the facility, and also to identify ways to audit the effectiveness of the training provided. Training of employees must meet requirements for both content and employee understanding. It is important for every employee to understand his/her role in the quality and safety of the product.


Validation of Processes and Procedures

Every process must meet certain specifications. Manufacturing processes require operating and critical tolerances. For every critical process, it is necessary to have a verification mechanism for the performance of that process. A well-designed analytical testing program provides critical, routine insight into the effectiveness of processes and procedures. If multiple failures occur, the question to ask is “Why?” and initiate corrective and preventive actions.

  • What were the failures?
  • What is the root cause?
  • Is there a pattern?
  • How can we test concerns related to failures?
  • How do we identify what needs to change?

An effective HACCP team reviews procedures and records regularly to maintain dependable product quality.

Commercial laboratories can provide key input in many of these areas. Validation testing, shelf-life testing, challenge studies, and other testing are available to support industry processes and product development. Consulting services from HACCP-trained laboratory professionals can also assist in the design of testing programs and troubleshooting to locate a problem’s source.

Contract laboratory audits provide insight into potential weaknesses in a system, resulting in opportunities for facility improvements. These improvements directly correlate with safer product manufacture. Similarly, training programs are available which couple a facility audit to customized training, maximizing the benefit to both employees and the facility.



There are numerous issues related to the control of Listeria in RTE food products. Operationally, to control Listeria requires attention at the front end of the process. Well-validated product design, processing, and sanitation lead to a safer product. Systematic and aggressive auditing uses a variety of tools to improve the process. Effective employee training clarifies lessons learned through auditing the process and provides opportunities to make the necessary improvements.