Manufacturers of ready-to-eat foods containing meat, poultry or seafood face an enormous challenge: keeping Listeria species, which are common in the environment, out of their finished products. Failure at this critical task may result in fatalities and illness to consumers from Listeria monocytogenes infection, as well as major losses to the producers responsible for the failure. The most troubling concern is that these failures occur in USDA inspected HACCP facilities, and are attributable to preventable causes.

Speaking microbiologically, Listeria species are considered an environmental organism – meaning that they occur naturally in the environment. They flourish at temperatures down to 3^oC (37^oF), and are resistant to heating and freezing. In the food processing facility or foodservice kitchen, any food residues remaining on food contact surfaces become a starting point for formation of biofilm, which provides harborage for bacterial contamination including notoriously the Listeria species. As a biofilm grows and hardens, it flakes off into subsequent batches of product, resulting in contamination of the product. Non-food contact surfaces and environmental areas may also harbor Listeria if sanitation procedures (SSOP’s) have not been followed correctly or are inadequate, providing sources of indirect contamination. Lastly, the facility’s “good manufacturing practices” (cGMP’s) may also contribute to contamination problems if they are inadequate, or if they are not followed properly and consistently.

How, then, must the problem of Listeria be controlled? What areas require specific attention in order to successfully and consistently produce safe RTE products? USDA’s Food Sanitation and Inspection Service (FSIS) has a zero tolerance rule pertaining to Listeria monocytogenes in ready-to-eat (RTE) foods containing meats or poultry, leaving no room for errors or oversights. There are four major areas of concern: sanitation, product design/handling/packaging, procedures and employee training, and validation of processes and procedures.

Sanitation

Control of Listeria must not be left to qualification of the finished product – it must be pushed upstream to the processes that are intended to keep the product safe. The most basic of these processes is plant sanitation. Equipment must be cleaned with appropriate cleaners and cleaning procedures to prevent buildups of residue that could lead to formation of biofilm. Cleaners must be appropriate to the types of residues that must be removed (alkaline for organics, acid for inorganics), and must be adjusted for the chemistry (pH, Hardness) of the plant’s water supply for maximum effectiveness. Temperature and contact time of sanitizers are all-critical factors. Environmental surfaces require careful attention, as potential indirect routes of contamination are abundant. Employees must be trained specifically to perform sanitation operations correctly, and training must be updated annually and as improvements are made. Validation of the sanitation process is critical, and must be accomplished by use of routine swab analyses to demonstrate the effectiveness of the process. An effective swabbing program may detect “positives” for Listeria from time to time. Where weaknesses are found, improvements must be made; this information will keep the sanitation team focused on eliminating the problem wherever it is found. Effective testing to support sanitation is the best way to identify and reinforce “best practices” regarding both SSOP’s and the sanitizers used, as well as supporting training of the sanitation team.

Product design/handling/packaging

The quality of the finished product is directly related to the quality of the raw materials. Raw material specifications are essential in controlling finished product quality, but it is also essential to know that the suppliers have effective control of Listeria in their own facilities – environmental organisms such as Listeria have been traced to the packaging of otherwise acceptable raw materials. Many successful facilities now use a combination of hurdle strategies, preservatives, and thermal or other lethality steps in their processing to obtain the optimum control of their product quality. Salt content, water activity, and pH control are three hurdles that may be used. Product preservation may also be achieved using either chemical or natural preservatives. Numerous preservatives are available on the market now; many companies are finding that certain pairings of preservatives are more effective than any individual compound. The most critical step in processing is the lethality step; this step must be validated on a regular basis, for every product, to demonstrate that the lethality step is indeed effective. Setting of appropriate operational tolerances is essential – using only critical limits does not allow for correction of the process before the end product has failed specifications. Post-lethality handling of RTE products must be carefully monitored to ensure that no contamination is taking place. In products such as cold-smoked seafoods, where there is no thermal processing, it is even more critical that the product design, handling and packaging all compensate for the lack of a “kill step.” Vacuum Packing (CVP) and Modified Atmosphere Packing (MAP) are two examples in which the packaging of the product can also play a key role in maintaining control of product quality. Finally, do not take the risk of assuming that your process is producing safe product without doing validation studies to demonstrate this fact. Changes of equipment (including changes resulting from aging), vendors, product formulation, and packaging are all sufficient reasons to re-validate a process. Current regulatory requirements, as well as Principle 6 of HACCP, require that validations be done; the regulatory expectation is that validations must be done in-plant, and must be based on sufficient scientific data. The net effectiveness of processing, preservative systems and packaging must be tested with challenge studies, shelflife studies and other testing as necessary to demonstrate that the entire process is in control.

Employee training

Proper implementation of your facility’s current Good Manufacturing Practices (cGMP’s), sanitation procedures (SSOP’s), and HACCP plan requires that employees be well-trained on an ongoing basis. How effective is your training program? How do you measure the success of your training efforts? Recent FDA data documents 1779 Class 1 recalls (those which are likely to result in serious human illness) in 2009 and 1499 in 2010, representing approximately 90% and 75% of all food recalls. (see http://www.leavittpartnersblog.com/fda-in-2010-a-bumper-year-for-recalls-a-review-of-the-reportable-food-registry-and-fda-recalls-10002530) Too frequently, issues either directly or indirectly relating to employee training deficiencies are found to be contributory factors in these situations. It is critically important not only to provide training that addresses the proper day-to-day requirements for the safe operation of your facility, but also to identify ways to audit the effectiveness of the training provided. Training of employees must meet requirements for both content and employee understanding. Every employee must be made aware that he has a key role in the quality and safety of the product, and every employee must be alert for opportunities to improve both his own performance and that of the processing operation.

Validation of processes and procedures

Every process must meet certain specifications. Manufacturing processes themselves require operating and critical limits. For every critical process it is necessary to have a mechanism to verify the performance of that process. A well designed monitoring program provides critical routine insight into the effectiveness of processes and procedures; if a pattern of failures appears, the correct use of that data is to ask “Why?” and initiate corrective and preventive actions.  What failures occurred? Why (root cause)? Is there a pattern? Was there a trend that led t the failure? How can we test concerns related to failures (every failure at a CP or CCP offers opportunity to improve – how do we identify what needs to change?). Someone has to ask the difficult questions; someone must identify the “didn’t think of that” concerns. Your HACCP team should be providing critical review of procedures and records on a regular basis. All of this is essential to maintaining dependable product quality.

Commercial laboratories can provide key input in many of these areas. Validation testing, shelflife testing, challenge studies, and other testing are available to support your processes and product development. Consulting services from HACCP-trained laboratory professionals can assist in design of testing programs and in troubleshooting to find the source of a problem. An audit by your contract laboratory can provide objective valuable insight into potential weaknesses in your system, resulting in opportunities for your facility to make improvements that result in a safer product. In the same manner, training programs are available which couple an objective audit of your facility to customized training, maximizing the benefit your employees, and your business, receive from that training.

Summary 

There are numerous issues related to the control of Listeria in RTE food products. Operationally, the battle to control Listeria is not won or lost in the final product, but rather 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 contribute continual improvement to the process. Effective training brings home to the employees the lessons learned through auditing the process and the opportunities to make the necessary improvements.

For more information, contact:
Dr. Kim Baughman, Director of Development
Microbac Laboratories, Inc.
kbaughman@microbac.com