Food Safety Magazine

COVER STORY | June/July 2003

Best Practices in Refrigerated Foods Processing

By Martin Mitchell

Best Practices in Refrigerated Foods Processing

Food retailers, foodservice operators and consumers who purchase products from the refrigerated, ready-to-eat (RTE) food industry are more aware of--and more demanding about--food safety than ever before. This raised consciousness of the last few years, along with new regulatory mandates and proposed rules that require increased compliance from all food industry sectors, has spurred the refrigerated foods industry to advance its efforts to find solutions and best-practice strategies that ensure the safety of its products.

The industry has been both proactive and reactive in terms of developing its own standards and best practices. In the past few years, refrigerated foods manufacturers have continued to make improvements to their Hazard Analysis & Critical Control Points (HACCP) programs. They also have introduced other useful food safety programs such as integrated quality management, a system that allows Good Manufacturing Practices (GMPs), Sanitation Standard Operating Procedures (SSOPs), HACCP and typical quality control (QC) functions all to coexist in one coordinated system. No single approach is used at the expense of another. The industry continues its efforts to identify microbiological concerns and meet associated requirements. Listeria monocytogenes remains at the top of the list of concerns given the pathogen's ability to grow at refrigerated temperatures, but the industry remains focused on developing preventive and detection methods for all microorganisms that pose food safety hazards.

As these general best practices for the refrigerated foods industry have evolved, so has our understanding of the new challenges that lay ahead. These include looking at emerging technologies carefully to evaluate the hazards that may be associated with these technologies before investing in them. A reevaluation of the shelf life of refrigerated, RTE items should make the safety aspect as much a factor as customer requirements. The industry must always search for better ways to educate food handlers and consumers about their roles in maintaining the safety and wholesomeness of these products.

There are a number of technological systems and methods that are or can be used to ensure the safety, shelf-life and temperature requirements of refrigerated, ready-to-eat food products. Each in the wide range of products in this category--from RTE meat products, to multi-ingredient salads, salsas and spreads, to puddings and prepared deli entrees--poses its own specific processing considerations. These technologies have achieved variable levels of success given the specifications of each product and its associated processing system. However, the need to maintain temperature, extend shelf-life and assure safe product has given rise to the use of many new and updated technological tools described.

Pathogen Reduction Technology
Both thermal and non-thermal methods that can be used to inactivate bacteria in food products or on food-contact surfaces have enhanced the refrigerated food company's ability to incorporate a multi-hurdle approach in reducing substantially the risk of releasing contaminated product. Non-thermal interventions available today are promising, including high pressure processing (HPP), novel chemical additives, chemical sterilants and irradiation technologies. HPP has had some very good success, notably with refrigerated guacamole product and now in RTE meal entrée production. The HPP automated system involves subjecting prepackaged and packaged food products placed in a vessel to ultra-high pressure of up to 100,000 psi for a few minutes. However, we need to allow this tool to develop its full potential to understand its effectiveness in eliminating pathogens, its organoleptic effect on the different kinds of products processed with HPP, and its cost-effectiveness.

One novel ingredient that we investigated at Certified Laboratories is NovaGARD CB1, a Rhodia Food ingredient. The product has been tested in numerous deli salads, including cole slaw, potato and seafood salads. Data generated in these tests show a rapid 3- to 5-log kill of Listeria monocytogenes in test salads, depending on usage level and product pH. Preliminary data suggests that this product may be useful for control of Clostridium botulinum in selected hot pack refrigerated foods when used in combination with appropriate formulation and processing requirements. Nova-GARD consists of a blend of natural Generally Recognized As Safe (GRAS) ingredients (cultured dextrose, sodium diacetate, egg white lysozyme and nisin) that are fully approved for use in a wide range of applications.

Similarly, irradiation will probably play a large role in refrigerated foods, once all necessary FDA approvals are finalized and products for which it is best used are identified. We must know to what extent these products can be treated by irradiation to attain pathogen elimination and still retain desired organoleptic characteristics. We know that irradiation is not to be used as a way to overcome bad sanitation practices or poor handling. General GMPs have to be applied, but irradiation technology gives the manufacturer the ability to give some of these products an in-package microbiological reduction that would result in an extended shelf-life and build in a level of safety that would be welcomed by all.

In some cases, such as in sliced or pre-cooked meat operations, post-packaging thermalization appears to have tremendous potential for the refrigerated foods industry. This approach is along the line of sous vide, but following the completion of the prep on the product and placing it into a hermetically sealed package, the processor can apply this level of heat to the item to kill any organisms that may have been introduced during slicing or other post-cooking handling. However, due to the reduced oxygen levels that occur, an awareness of the anaerobic pathogens must be considered. The use of challenge studies would be one way to better understand the risks.

Advances in chemical treatments to inactivate pathogens in foods also have proved useful to the refrigerated foods industry. The Refrigerated Foods Association (RFA) conducted a study two years ago comparing and evaluating different chemical processes, such as ozone, chlorine dioxide, peroxyacetic acid and acidified sodium chloride, to determine their efficacy in reducing microorganisms in fresh-cut celery. This is important to the refrigerated food manufacturers, many of whom use celery, cabbage or other vegetables to make their finished products. In this particular study, chlorine dioxide was determined to be the most effective. Ozone was deemed a powerful tool, but perhaps the treatment times or levels may need further study. The industry continues to explore the various chemical sterilants available that can be applied safely to raw produce and other ingredients.

Recently approved for use as a pathogen decontaminant in foods and on food-contact surfaces, ozone technology is another chemical treatment that holds promise for the industry. This oxygen-based gas eliminates microorganisms via oxidation reaction. Several industrial studies on the use of ozone in direct contact processing applications have shown that, when used in conjunction with filtration systems and ultraviolet (UV) light, the treatment reduced the bacteria on items such as fresh-cut salads and fish and extended the shelf life of these products.

Testing Methods
Rapid microbiology methods that were rarely used 10 years ago today are used regularly both by independent food testing laboratories and food processor's in-house labs. The food industry's need for quick product turnaround, particularly perishable items, has been a tremendous impetus in the development of many commercial "real-time" diagnostic test kits and automated systems.

One of the most promising is polymerase chain reaction (PCR), which has become even more specific and more rapid in the past few years. This type of testing capability is important to refrigerated foods manufacturers, not only in terms of rapidity of results but because of its specificity. In this way, the processor can quickly tell whether the bacteria present is Listeria monocytogenes versus a Listeria strain that does not pose a hazard to human health. Other rapid methodologies such as enzyme-linked immuno-sorbent assay (ELISA), enzyme-linked fluorescent assay (ELFA) and selective culture media also have contributed to the industry's testing toolbox.

Listeria monocytogenes remains the refrigerated, RTE food manufacturer's top microbiological safety concern. Although there has been an evolution in our ability to identify and rapidly test for Listeria monocytogenes, the industry needs to embrace increased testing efforts. Unfortunately, the lawyers became involved with the Listeria issue at the same time that the scientists did, and as a result, there has been a resistance to look for Listeria monocytogenes on finished product or on food contact surfaces because of the risk of regulatory or legal action if it is found. But without extensive testing to help find harborages or sources of the contamination it is similar to walking blindfolded through a minefield. Because of this resistance to look, the industry settled on environmental testing and did not include finished product and contact surfaces.

This may be understandable, but aggressive testing of product contact surfaces for the presence of either Listeria spp. or Listeria-like organisms is both good science and a good regulatory/legal approach to the problem. In fact, increasing the amount of testing that we do on product and product contact surfaces--before, during and after production--would actually allow us to find Listeria-like organisms so that plant personnel can eradicate these harborages or niches in which it exists. On an encouraging note, the Listeria risk assessment recently issued by the U.S. Department of Agriculture (USDA) appears to address this disincentive, and there seems to be a softening of the view that the discovery of a Listeria-like organism in a food plant is a regulatory event.
Sanitation Technology

Although we like to talk about "whistles-and-bells" advances in new technology applications, the fact is that the industry is returning to the basics with regard to sanitation tools and approaches. There are a lot of improved and environmentally-friendly chemical sanitizers available for use in food processing sanitation activities, new automated chemical dispensing and application systems, and better environmental monitoring verification tools such as adenosine triphosphate (ATP) tests that allow quality control staff to better clean and to monitor the clean-up crews' job.

While all of these developments aid the manufacturer in reducing potential food safety hazards in the plant environment, the industry understands that achieving a sanitary environment involves a whole systematic approach to be successful. A good program is a system of cleaning and sanitizing equipment that encompasses design, dismantling, proper cleaning and removal of interferences like biofilm and minerals, proper application of environmentally friendly sanitizers, followed by monitoring to verify effectiveness using ATP. The manufacturer should not put too much emphasis on any one part of this system; each step is as important as the others.

The basics of good food plant sanitation is two-fold. First are the fundamentals of sanitary equipment design. Historically, there were several protocols that encouraged sanitary design, including the now-defunct USDA program for approving equipment for use in food processing and state programs that required equipment to pass an inspection before a company could install it in the plant. In the recent past, however, there was a diminution in the way the industry and the regulators set standards for the sanitary design of equipment, which resulted in a movement away from these good-sense standards. As a result, and all too often, equipment salespeople began to tout the efficiencies of the pieces they sold to food plants, but never spoke to plant personnel about how to properly clean. As a result, the industry had poorly designed equipment that was difficult to clean or was being disassembled and cleaned by people who did not have proper training. Such equipment could be a potential source for microbiological contamination.

Currently, there is a shift back to an understanding that equipment needs to be properly designed to prevent foodborne contamination. This is evidenced by industry efforts such as the development of the American Meat Institute's (AMI) 10 Principles of Sanitary Design and renewed attention by the equipment manufacturers who are beginning to provide better information to plant personnel on how to clean their (it is hoped) better-designed equipment.

Second, there is a return to the basics of proper cleaning methods in the food industry. While there are many more chemical sanitizers available for use in food processing sanitation activities, the manufacturer recognizes that he cannot rely solely on chemical treatments to assure sanitation. The fact is, you can take the world's greatest chemical sanitizer and properly apply it, but if you apply it to an improperly cleaned piece of equipment or on top of a biofilm, you are not going to successfully sanitize it. You cannot sanitize dirt, and the only way to eliminate dirt or other residue build-up on the equipment surface is to completely dismantle and clean the equipment using abrasion and strong alkali to remove the biofilm to allow the sanitizer to have direct contact with the equipment surface.

Shelf Life & Temperature Control
In October 2002, the author and Dr. Catherine W. Donnelly of the University of Vermont, presented the RFA Protocol for Determining the Shelf Life of Refrigerated Foods (www.refrigeratedfoods.org). The aim of the association in sponsoring this work was to establish a standardized protocol by which individual manufacturers may determine the shelf life of their product and its safety. Consideration in developing this protocol was given to product handling during shelf life by consumers; holding temperatures that are appropriate for shelf life determination based upon product handling; the nature of product composition, i.e., whether the refrigerated foods contain preservatives; and the nature of the packaging material used and whether products were packaged under modified atmospheres or had pH adjustment to extend shelf life.

In addition, a risk assessment was conducted for specific refrigerated products--potato salad, tuna salad and refrigerated pizza--in order to determine how criteria for refrigerated shelf life based on safety could be accomplished. In assessing the risks posed by foodborne pathogens in these products, consideration was given to the food characteristics, including potential microbiological hazards and the history of causing food-borne illness. Due to the ubiquitous nature of Listeria monocytogenes, its potential for growth at refrigeration temperatures and its high mortality rate, it was considered a pathogen of primary concern in these products. The risk of Listeria outgrowth in these products is a function of pH, temperature, salt concentration, Aw, and the presence of other inhibitory substances such as preservatives. If products are packaged under reduced oxygen conditions, consideration was given to performance of challenge studies that consider risk of Clostridium botulinum outgrowth using Clostridium sporogenes as a surrogate. Microbiological parameters were established to dictate shelf life based upon a log growth tolerance.

The procedure proposed for this shelf life protocol for refrigerated foods provides a framework for determining the shelf life of all refrigerated foods so that microbiological criteria, chemical analysis and sensory profiles are compiled over time to observe the maintenance of quality and safety throughout the shelf life of these products. Although this is a tremendous first step in maintaining product safety and functionality, there remain issues of concern. One of these areas is the lack of consistency in temperature control and the way in which refrigerated food products are handled, as illustrated by a 1999 Audits International study (Table 1).

The survey revealed that 41% of retail food product temperatures were in the range of 41-50F, while 6.7% of products were at temperatures between 51-65F. Thus, in determining the shelf life of refrigerated foods, the potential for product to be held under less than optimal conditions must be considered and the potential for growth of spoilage flora and pathogens carefully evaluated. It is essential to ensure that refrigerated foods do not support rapid growth of pathogens during periods of temperature abuse by consumers and retailers. The food manufacturer may determine that the stated shelf life of his product requires that it should be held at 36F, but if in reality the product is being held at 45F, there will be an entirely different shelf life and safety profile for that product. The unanswered question, then, is what is the real-world temperature profile for my product and how does that impact on the safety and quality of the product?

MAP and Packaging Technology
As an industry, RTE foods manufacturers use modified atmosphere packaging (MAP) technology. There now are more "intelligent" MAP packages available to the food industry, including those in which respiration has been enhanced and those that offer the opportunity to adjust and test different atmospheres to augment the shelf life of a specific product. These have great potential, although we must be prepared for some risk. MAP packaging does have some safety considerations because Listeria and Clostridium botulinum have the ability to grow anaerobically.

Traditionally, refrigerated foods would have organoleptically spoiled before they would get someone sick; in other words, before the food would allow for the overgrowth of these organisms. Once the package atmosphere is modified with nitrogen, carbon dixoide, vacuum or a noble gas, it becomes favorable for these anaerobes to grow, and perhaps outgrow and develop toxins before the food becomes organoleptically unfit. This is why the RFA Shelf Life Protocol suggests that before the manufacturer opts to MAP package his food products, the packaging must be validated using a challenge study to make sure that, in fact, it won't support the rapid growth of these undesirable organisms.

Managing the Next Big Things
HACCP is the current management philosophy behind food safety. The refrigerated foods industry has embraced this program to good effect and has not overlooked the fact that manufacturers need to establish and install good basic prerequisite programs such as GMPs and SSOPs. The food industry now has a new component for its food safety efforts: food security. While not the equivalent of the food safety program, it is an important part of management's responsibility to build food security measures into plant operations. This means a renewed focus on employees and the plant perimeter more than ever. For food to be made safe and secure by the people in the plant doing the job, the emphasis on educating employees to understand their role and the role of the operations they control within the food safety framework is more important than ever. It is imperative that the manufacturer make sure that the people who have access to the product are cleared for food security purposes and receive the training that they need to understand food safety.

The refrigerated food manufacturer must work closely with foodservice operators, service delis and retailers to ensure proper storage, hold times and food handling. Any time a person touches the product, the risk of cross-contamination is raised. Hand washing is the single most important control to combat this potential problem. The potential for the foodservice worker to contaminate a tray of product is exacerbated if the product has a reasonably long shelf life. It may allow enough time in the display case or in the bain marie for the contaminant organisms to grow. Another risk at the foodservice end involves instances in which food handlers take a basic product made by a refrigerated foods manufacturer and dress it up by adding protein or other garnishes. If the same care is not taken with the added protein or garnish that was taken during the original manufacturing, there could be a contamination situation.

The refrigerated, RTE foods industry today not only is better prepared for safety in terms of product design, processing and handling, but is actively preparing for future challenges in order to prevail against barriers to the protection of the food supply. According to recent statistics, there appears to be a decline of foodborne illness in the U.S., which provides encouragement to all of us all who expend our efforts in food safety.

Martin Mitchell is Managing Director of Certified Laboratories, an independent food testing contract laboratory established in 1926, employing more than 100 people in two facilities in Anaheim, CA and Plainview, NY. For 25 years, Mitchell has been the technical director of the Refrigerated Foods Association, the leading international association of manufacturers and suppliers of refrigerated foods, including producers of wet salads, home meal replacement options, and refrigerated entrees, desserts, side dishes and ethnic foods. His technical expertise includes all aspects of food processing, sanitation, technology and equipment. Readers may contact Mitchell via e-mail at mmitchell@800certlab.com.

Categories: Contamination Control: Microbiological, Reduction Methods; Food Types: Ready-to-Eat, Refrigerated/Frozen; Process Control: Packaging; Regulatory: HACCP; Sanitation: SSOPs; Supply Chain: Temperature Control/Cold Chain; Testing and Analysis: Methods