Safety Of Chilled Foods

By: Bruce M. Floyd
Contributing Editor

  As the U.S. food market moves increasingly toward "fresh" foods, the market for chilled foods is also growing rapidly. In the foodservice area, menu items are often partially prepared outside the restaurant, either in company-owned commissaries or by third-party processors. Some of these items are ready-to-serve, such as salad-bar items, while some need further preparation in the kitchen prior to serving. Minimal processing is the key, so that the food appears "freshly" made.

  In addition, more people are consuming convenience foods and eating in restaurants. Fewer meals are prepared from scratch, fewer people know how to cook, and home meal replacement (HMR) has made it possible to pick up dinner on the way home and reheat it in the microwave. All these factors contribute to the importance of making sure chilled foods are as safe as possible.

Clean living

  Thanks to improved processing facilities from farm to table, the cleanliness of the basic food supply has improved. The basic foods consumers eat have a longer shelf life and less filth (bugs and excreta) than in the past. Food is processed in larger plants and shipped longer distances due to advances in processing and packaging technology. Modified atmosphere packaging (MAP), other packaging advances and improved processing techniques allow significant increases in the shelf lives of perishable products.

  As the food supply has become cleaner, however, E. coli 0157:H7 and L. monocytogenes have become a general public-health problem. In other words, reducing harmless microorganisms to extend shelf life has contributed to the current food-safety problem. According to James M. Jay, Ph.D., adjunct professor, department of biological sciences, University of Nevada-Las Vegas, prior to 1982 there were only three cases of foodborne illness traceable to ground beef. "The gist of microbial interference relative to the safety of fresh foods is that a product that contains, say, 105 cells/g of harmless micro biota is less likely to allow low numbers of pathogens to proliferate than one that contains, say, 103 cells/g," he says in an article entitled "Do Background Microorganisms Play a Role in the Safety of Fresh Foods?" in the December 1997 Trends in Food Science and Technology.

  Meanwhile, the number of "at risk" people is not limited to a small percentage of the population. Listeria, for example, puts all pregnant women at risk. The government defines "at risk" people as children, the elderly, and persons with weakened immune systems, which includes those with HIV and those undergoing chemotherapy, as well as pregnant women.

  It’s a good idea to test for harmful pathogens in food. Keep in mind, however, that the testing procedure must address the risks associated with a particular food and delivery system. (For more information, see "Testing for Foodborne Pathogens" in the July 1999 issue of Food Product Design.) To become acquainted with the various harmful microflora that could be living in chilled-food products, consult the FDA’s Bad Bug Book, available online at http://vm.cfsan.fda.gov/~mow/ intro.html, or hire a microbiological consultant with experience in your industry.

Chilled-foods round up

  The chilled-foods category encompasses the following products:

• Refrigerated, processed ready-to-eat (RTE) foods, including bottled milk products, processed or cultured dairy products, lunchmeat and other pre-cooked meats, sandwiches, fresh soups, sauces, HMR products such as meatballs and barbecue beans, meat salads, custards, quiches, fruit salads and sandwich fillings. Although some of these are reheated prior to serving, they do not require a cooking step.
  
• Raw or partially prepared products intended to be cooked by the final user, such as refrigerated dough products, meat and fruit pies, breaded pork chops, deli pizza and central commissary products.
  
• Raw products intended to be cooked prior to serving, including fresh meat and poultry products and many commissary items such as breaded shrimp and marinated meats.
  
• Raw food products that will not be further processed by the final consumer, such as pre-cut vegetables and fruits.
  
• Products that are an amalgam of the above.
  
• Products with extended shelf lives due to changes in the atmosphere within the package from MAP or sous vide packaging.
  

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    Note that terminally sterilized products that are distributed refrigerated, such as a UHT-processed, individually packaged half-and-half, or Sport Shake™, a drink with a 15-month shelf life, are not considered chilled foods.
  

    Chilled foods, while convenient, unfortunately lend themselves to consumer and distribution abuse. There are four sources of harmful bacteria in food — the environment where the raw food is produced, the equipment in which the food is processed, the packaging materials used, and post-processing contamination during distribution and use.
  

  Environmental impact
  

    The environment holds the key to many food-contamination problems. Microorganisms such as E. coli and Salmonella show up on fruits and vegetables entering food plants. Listeria and other bacteria are very widely distributed in the environment, and pose an industry problem.
  

    Birds flying over fields and collection points and congregating at plant unloading areas are an old, but continuing, problem. Large numbers of meat and dairy animals are raised in a single location, facilitating the spread of microorganisms. Also, spreading manure on croplands allows wind-blown dust from the fields to carry pathogenic bacteria to row and tree crops. Contaminated irrigation water can contain pathogenic bacteria, as well as parasitic organisms.
  

    Preventing bacteria from spreading from one animal to another is a hot research topic, although no clear answers are readily available. The possibility of minimizing E. coli 0157:H7 by changing the diet of ruminants is being examined; one experimental technique involves establishing non-harmful, competitive microorganisms in the animals’ digestive tracts.
  

  Equipment issues
  

    "Ninety-nine percent of all contamination problems in processed foods — either pathogens or spoilage organisms — are related to improper cleaning and sanitizing of the equipment," says Ed Zatola, Ph.D., professor emeritus, University of Minnesota, and consultant for Lansi Bay Company, Cook, MN. "A major problem associated with proper cleaning and sanitizing is related to the proper design of the equipment."
  

    Gerald Sapers, Ph.D., a research food technologist with the USDA-ARS Eastern Regional Research Center, Wyndmoor, PA, points to a test run at a full-scale apple processing facility that the FDA operates. In the test, apples inoculated with E. coli were processed. After cleaning the equipment, a non-inoculated batch of apples was processed. Both batches tested positive for E. coli. Sapers attributes this both to the difficulty of washing the equipment, which included a hammer mill, and to the tendency of bacteria to form biofilms. He also notes that the outside of fruit must be washed free of bacteria, because once it’s cut, bacteria can lodge underneath a layer of fruit tissue, making it difficult to kill the bacteria with a sanitizer.
  

    Biofilms tend to flake off equipment randomly, making low-level contamination difficult to find. Note that this is not similar to an entire tank of apple juice being contaminated. In such a case, the entire contents would have some level of the organism present. Random contamination from improperly cleaned equipment — especially equipment with a design defect — tends to be spotty, however. Certain portions of the run may be more likely to show contamination than others, but this depends on the product and method of operation. Not only does equipment have to be designed for easy cleaning, but it also has to be sanitized by a method that disrupts biofilms.
  

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    A good equipment-swabbing program after wash-up will help detect problem areas, particularly after the sanitizer has dissipated, allowing the bacteria to grow. For example, the Monday morning after a weekend shut-down is a good time to swab.
  

    Contamination in hard-to-reach areas does not show up immediately after a wash. Sometimes it’s necessary to run the equipment for a few minutes before swabbing to find these areas. There might be drainage or flaking from a hidden area into the product. A nagging problem with no specific cause in an area may require taking all the equipment apart before the defect is found. It’s also possible that another source, such as overhead condensate, is re-contaminating equipment.
  

    In the absence of minimum equipment-construction standards (such as the 3A standards for dairy equipment) for the entire food industry, it’s best to purchase only easily cleanable equipment. It may cost more initially, but in the end, it will save operating costs and minimize product rejections due to contamination.
  

    In the foodservice industry, the independent organization NSF International (www.nsf.org), Ann Arbor, MI has been developing standards for foodservice equipment for 50 years. An equipment-approval program is one of the many services they offer.
  

  Safe packing and traveling
  

    Contamination of pre-cut fresh fruits and vegetables distributed in MAP containers can be a concern. "The longer shelf lives (10 to 14 days) that are now common, due to sophisticated packaging and good temperature control, may provide sufficient time for some pathogens to reproduce that normally would not have been able to reach problematic levels in shorter time periods," says John Williams in volume 14, number 3, 1999, of Silliker Laboratories’ Scope Technical Bulletin. "Modified atmosphere packaging may suppress spoilage organisms that organoleptically signal the end of shelf life. Outgrowth of potentially pathogenic organisms, should they be present, could occur without altering the sensory properties of the product, resulting in the loss of a warning signal to the consumer that the product may not be safe." Cutting produce exposes fresh surfaces to equipment contaminants without any other microbial competition present, giving the "bad guys" a clear field in which to reproduce.
  

    Another challenge with chilled foods is knowing what happens to them after they leave the factory. One tool to help keep track of chilled foods’ travels is a temperature-abuse indicator. LifeLines Technology, Inc. (www.lifelinestechnology.com), Morris Plains, NJ, markets one such device under the Fresh-Check brand name. This thermally irreversible temperature indicator is customized specifically for various products, and can be designed to change over different time periods at various temperatures and with accumulative heat exposure. The product can be applied to the shipping container as well as to individual packages. Once the indicator has turned color, the product is no longer safe to consume.
  

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  Preventive measures
  

    As an anti-microbial, ozone has several useful attributes. Used for many years to purify water, ozone also attacks biofilms on equipment and is effective against a wide variety of microorganisms. Ozone breaks down quickly, with an average life in solution of 25 minutes. It does not produce harmful chemical byproducts, and is environmentally friendly. It can be dissolved in water, or used as a gas. In combination with an adequate filtering system, ozone can be used to treat flume water, equipment rinse water and product wash water, killing bacteria on contact.
  

    Ozone as a sanitizer is gaining popularity as equipment for its in-plant use has become more available. "Ozone offers a real advantage over bleach and other disinfectants because of its strong oxidizing power. It will disintegrate biofilms; destroy pyrogenic lipopolysaccharides (gram-negative bacteria endotoxin), total organic carbon (TOC) and inorganic matter. Conventional chemical disinfectants can not compare to the efficacy of ozone," says Rebecca L. Amato, R.N., B.S.N., C.N.N., in the December 1998 Contemporary Dialysis & Nephrology. Ozone is effective against many organisms that are resistant to chlorine, and it does not tend to produce off-flavors.
  

    Research on cold storage for fruit in an atmosphere supplemented with ozone has revealed that shelf life can be significantly extended. Ozone gas can also improve the environmental quality of cold storage areas. In fruit washes, it can reduce the numbers of protozoa such as cyclospora. Additionally, recent articles have appeared on the purification of poultry chiller water with ozone. Unfortunately, ozone does not reach 5-log reductions in all applications; however, used in conjunction with other methods, it can go a long way toward improving the quality and safety of chilled foods.
  

    Electronic pasteurization offers another way to fight pathogens. "In the future, people would no sooner feed their children unpasteurized meat than they would give their children unpasteurized milk today, and for the very same reason," says Wil Williams, vice president of corporate communications, Titan Corporation, San Diego, CA. Because its electronic food pasteurization system uses ordinary electricity, it presents an environmentally safe alternative to radioactive elements such as cobalt 60 or cesium 137, says the company.
  

    Electronic pasteurization generates high-energy electrons that quickly pasteurize foods and destroy E. coli, Salmonella, Campylobacter and Listeria monocytogenes on meat, poultry, fruits, vegetables and grains. Because electronic pasteurization treats products that have already been processed and packaged, post-processing contamination is eliminated.
  

    It’s important to note that pasteurization is not sterilization. The cGMPs (Current Good Manufacturing Practice for the Manufacturing, Packing or Holding of Human Food as found in 21 CFR 110) must be followed, and it’s necessary to handle product properly during subsequent transportation and storage. Also, since pathogens are susceptible to electronic pasteurization at lower exposure rates than are some non-pathogenic spoilage organisms, the shelf life of the product may not be enhanced. Like all food processes, it’s necessary to conduct field trials to determine the overall effects on a specific product or process. Electronic pasteurization does not replace good sanitation practices, although it is an additional tool in the quest to provide the consumer with safer food.
  

    Electronic pasteurization was approved by the USDA’s Food Safety Inspection Service in December of 1999 for use on meats, including fresh ground beef. It had previously been approved for poultry, and the FDA had also previously issued its approval.
  

  Chilled-food challenges
  

    Due in part to the government’s new Food Safety Initiative, food-safety research is being carried out at an accelerated level by not only the government, but the academic community and industry as well. For example, the USDA-ARS Eastern Regional Research Center is conducting research on a variety of chemicals and plant extracts that possess antimicrobial activity.
  

    Safety of chilled foods, as with other parts of the food supply, must be attacked as a system, with no magic bullet available to solve the entire problem. One factor that would help, however, is equal enforcement of regulations, making the playing field level for all. Such enforcement should also be extended to imported products so that all products compete on the same basis of food safety.
  

    With industry willing to install systems that minimize contamination, private initiatives are available to help develop systems with practical application. Most of what’s discussed isn’t cheap, but holds promise of greatly reducing the risk of spreading foodborne illness, as well as reducing the risk of a crippling recall. Remember though, that these systems are just a part of an overall system based on sound sanitation and processing techniques — there are no shortcuts to safety.
  

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    The Chilled Food Association (CFA), with offices in London, UK, is an industry association promoting high standards of hygiene. One of its handbooks, Guidelines for Good Hygienic Practice in the Manufacture of Chilled Foods, covers many facets of processing, packaging and distribution.
  

    Under the food-safety section of its website at www.chilledfood.org, the association offers the following advice: "MAP or vacuum packaging may be used to reduce microbiological growth but will not necessarily inhibit the growth of pathogens. There may be particular concerns with respect to Clostridium botulinum. It is important that the effectiveness of MAP or vacuum packaging is assessed in each case, with reference to specialist advice." This illustrates how important it is to understand the potential for unexpected events when adopting new technology.
  

    Chilled foods offer many challenges. Food safety cannot be tested into a product, but must be designed into a process along with efficiency and quality. It’s also important to use new technology wisely. Many times, the rush to market minimizes the importance of doing a thorough risk analysis of the new system. By re-examining each product and process at the fundamental cGMP level and adopting proven technologies as they become available, companies can minimize a great deal of their risk.
  

  Bruce Floyd established Process Systems Consulting, Iowa City, IA, after working more than 30 years in the food processing industry. He has had extensive experience in sanitation, quality control, regulatory relations, and product and process development (both domestic and international), and specializes in integrating ingredient and manufacturing specifications into total process systems. A graduate of Georgia State University, he has successfully completed all areas of the Better Process Control School at the University of Minnesota, and has been qualified by the International HACCP Alliance as an instructor. He can be reached via e-mail at bfloyd7192@aol.com.

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