Extending the Shelf Life of Refrigerated Foods: For Better or Worse?

February 1, 1998

First published in Food Technology Magazine, February 1998. (Download PDF version)

The convenience and enhanced quality of mildly processed refrigerated foods make them an attractive, highly profitable opportunity for food processors. However, there are many safety and quality complications that the food industry must consider in marketing refrigerated foods, especially those with extended shelf lives. The Scientific Status Summary, “Extended Shelf Life Refrigerated Foods: Microbiological Quality and Safety” (see pages 57–62) prepared for IFT’s Expert Panel on Food Safety and Nutrition by Elmer Marth, addresses many of these issues.

Consumer preference for fresh-like foods that are ready to eat or easy to prepare make refrigerated foods that receive minimal processing among the most rapidly growing segments of the food processing industry. Fresh-cut packaged produce, for example, has been resoundingly accepted by consumers. Freshcut vegetable processors provide prepackaged dry salads such as cut lettuce, carrots, broccoli, and other vegetables in various combinations that are prewashed and ready to eat. This industry has within a few short years grown from less than $1 million to more than $1 billion in annual sales. Similar opportunities are predicted for fresh-cut packaged fruit.

Among the foremost of considerations that processors must address before investing in new product lines of refrigerated foods is the microbiological safety of such products. As explained by Marth in the Scientific Status Summary, some bacterial pathogens such as nonproteolytic Clostridium botulinum and Listeria monocytogenes can grow, albeit slowly, at refrigeration temperature. Temperature control in refrigeration units of retail outlets and homes, however, is frequently unacceptable for perishable foods that rely solely or largely on refrigeration temperature to control foodborne pathogens. Studies have revealed that a significant number of home and grocery store refrigerators operate at temperatures above 10°C (50°F). Not only can a variety of spoilage and pathogenic bacteria grow at these abusive temperatures, but psychrotrophic bacteria, which grow at refrigeration temperature, can proliferate more rapidly above 10°C.

Another important consideration described by Marth is the quality of refrigerated foods. In addition to the enzymatic and chemical degradation that occurs in fresh-like foods, many types of microbes can grow at chill temperatures and spoil products. To avoid premature spoilage of products, processors must have stringent control of the levels of microorganisms in ingredients used in refrigerated foods.

Stringent temperature control is the most critical factor for ensuring the safety and quality of refrigerated foods. The second most critical factor is an acceptable (preferably short) product shelf life. Processors who increase the shelf life of refrigerated foods without including effective barriers to microbial growth greatly increase their risk of selling unsafe or poor quality product. Establishing the shelf life of perishable refrigerated foods requires careful experimentation, evaluation, and sufficient validation. Processors must realize that simply putting a later expiration date on a highly perishable product’s package to match that achieved by a competitor using innovative approaches to extend shelf life is not an acceptable alternative.

One of the greatest marketing advantages used by processors of refrigerated foods is extension of the product’s “use by” date. A variety of barriers to microbial growth has been developed and innovative approaches are under development; however, processors must be vigilant in applying such antimicrobials by assuring that a potential microbial safety problem is not introduced as a result of controlling spoilage microorganisms. For example, some treatments such as modified atmosphere packaging in oxygen impermeable films may greatly extend the shelf life of a perishable food, like fresh-packed sliced mushrooms, but may create conditions that would enable harmful microorganisms, such as Clostridium botulinum to grow to dangerous levels. Processors should solicit the input of qualified food microbiologists to fully evaluate the safety of treatments used to extend product shelf life before implementing such practices.

Clearly, consumer interest in minimally processed refrigerated foods that have remarkable quality, enhanced nutrition, and added convenience is driving processors to market such products; but some may be on the edge of safety, especially if temperature abuse occurs. Processors attempting to meet consumer demand for products with inherent microbiological risks should be diligent in fully evaluating and preventing the hazards that may exist in refrigerated foods with extended shelf lives before marketing such products.

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