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From: Food Quality & Safety magazine, December/January 2008

Top Shelf Quality

Shelf-life and challenge studies play a key role in validating quality and safety

by Arthur Rumpf

Over the years, science and technology have led to a much better understanding of the underlying principles that make certain preservation techniques work. Some of the more common preservation techniques—heating, chilling, drying, salting, acidification, oxygen removal, and fermenting—have been in use for a long time.

Newer preservation techniques to increase shelf life continue to be developed, however. This research is being conducted to meet the demands of health-conscious consumers who want to purchase foods—those that are low fat, low salt, or lower in sugar, for example—that challenge current practices for providing safe, shelf-stable food. While scientists and technicians continue to try to meet these demands, the potential risk to food safety and quality tends to increase. This danger places more emphasis on adequate shelf-life and challenge studies that are needed to validate any changes (Table 1, p. 37).

Shelf-life studies are primarily conducted to determine and validate the length of time a food will retain its quality under a given set of storage conditions from the time the food is prepared or manufactured. During the shelf life of a food, it should be safe to use, it should retain the expected quality attributes characteristic of the product, and it must meet any nutritional claims indicated on the label.

Challenge studies are typically used to assess whether formulation and storage conditions for a food can control the growth of any pathogens present during the designated shelf life. The procedure involves inoculation of the product with relevant microorganisms, followed by incubation under controlled environmental conditions in order to assess food safety as well as quality.

Ensure Safety and Quality

Shelf-life and challenge studies are extremely important to ensure both safety and quality of food products prior to their final release to consumers. By conducting these studies, the food manufacturer ensures that consumer and regulatory expectations for safety and quality are met and helps avoid potentially expensive product recall and liability situations. Food manufacturers are always interested in maximizing shelf life to reduce costs; conducting these studies assists in these efforts.

For new products, these studies should be done during the product-development cycle. They should also be conducted any time there is a change in formulation, processing operations, packaging components, and storage conditions.

The food manufacturer or preparer should have management-of-change procedures and hazard analysis and critical control point (HACCP) plans. These should define the requirements and reference the procedures required for conducting studies whenever any changes take place in the factors listed above.

Conducting Shelf-Life, Challenge Studies

Shelf-life and challenge studies should be carried out in an objective manner for each type of product. The studies should use defined protocols that outline the tests, number of samples, conditions, and outcomes expected, as well as the responsibilities of those involved.

There are basically two methods for conducting shelf life and challenge studies. Direct methods store the product under predetermined conditions for a period greater than the expected shelf life, checking the product at regular intervals to determine when it begins to deteriorate. This determination is typically made using a combination of sensory, chemical, and microbiological testing.

Indirect methods attempt to predict the shelf life of a product without running a full-length storage trial and are most often used for products with a longer shelf life. Indirect methods may use accelerated environmental conditions (e.g., temperature) to increase the rate of deterioration. They may also include predictive modeling that utilizes mathematical database models to calculate bacterial growth, but this approach depends on knowledge of the product’s properties to provide input for the calculations. Either of these two methods should follow a step-by-step process (Table 2, p. 37).

Knowledge of a food’s formulation and history, such as association with known illness outbreaks and/or evidence of potential growth, is essential when selecting the appropriate challenge pathogens. Information from the U.S. Food and Drug Administration’s Center for Food Safety and Applied Nutrition describes some pathogens that may be used in challenge studies for various types of foods (Table 3, above).

Costs and Resources

Shelf life and challenge studies can be costly and time consuming if not done effectively. If, for example, potential causes for spoilage are identified in the first step of the process outlined in Table 2 and can easily be overcome by a slight formulation or process adjustment, it may be better to revise the product under consideration with these adjustments prior to initiating the study. If optimal storage conditions involve freezing the product, the value of a challenge study should be questioned.

It is essential that subject matter experts in food safety, quality, formulation, and packaging help design the studies and evaluate the results. Enlisting third-party consulting resources and testing labs helps ensure the effectiveness and adequacy of these studies.

Design of experiment (DOE) is a systematic approach applicable to shelf-life studies in which planned changes are made to the input variables of the process or product. The effects of the changes are assessed to maximize information gained while minimizing resources required. DOE has more to offer than “one change at a time” experimental methods, because it judges the significance of input variables acting alone on the output, as well as input variables acting in combination with one another.

Another key to testing success is understanding the requirements and wording used when translating the shelf life determined by a study into a working shelf-life standard used for dating a food product. State and local requirements differ, as do the requirements of different countries, so this area must be fully researched for the specific product, packaging, and market area being serviced.

On an international level, the Codex Alimentarius helps define international standards and guidelines on food labeling relating to date-code marking. In the United States, there is no uniform or universally accepted system used for food dating. Although dating of some foods is required by more than 20 states, there are areas of the country where much of the food supply has some type of open date and other areas where almost no food is dated. Except for infant formula and some baby food, product dating is not generally required by federal regulations. If a calendar date is used, however, it must express both the month and day of the month (and, in the case of shelf-stable and frozen products, the year). If a calendar date is shown, a phrase explaining the meaning of the date—such as “sell by” or “use before”—must be placed immediately adjacent to the date (Table 4, p. 40).

In section 3-501.17, the 2005 Food and Drug Administration (FDA) Food Code adopted by many states identifies date-marking requirements for retail food establishments for ready-to-eat, potentially hazardous food. In some cases, selling food past the expiration date is not a violation of FDA regulations or law. The quality characteristics of foods (taste, aroma, and appearance, which are distinct from safety characteristics) often depend in large part on ideal storage conditions that rely on temperature and humidity control in the retail store and warehouse. Under optimal storage conditions, many foods are acceptable in terms of taste and other quality characteristics—and are safe to eat—for periods of time beyond the expiration date printed on the label.

Taste and other quality characteristics deteriorate more rapidly if the food is stored at elevated temperatures and in high humidity conditions, a situation that might occur if the air conditioning fails in a retail store, warehouse, or in the consumer’s home. Conversely, deterioration occurs very slowly if foods are stored under optimal conditions with correct temperatures and low humidity.

Because the expiration date is not indicative of product quality if storage conditions have been less than optimal, the FDA does not require expiration dates on most products. An exception to this rule is the expiration dates required on drugs. The dates required on infant formula products are “use by” dates, not “expiration” dates. A consumer using the infant formula product before this date is assured that the product meets nutritional and quality standards.

There are additional considerations:

  • Be sure that the food in any shelf-life study is safe to consume prior to use in a taste-panel evaluation;
  • Any time there have been changes in the production or processing environment, the shelf-life study should be repeated;
  • Do not rely on accelerated tests or predictive models alone to justify a shelf life. When using these indirect methods, be sure to continue to monitor the product for the full shelf life to ensure it is safe and meets quality requirements;
  • Fully document the stability protocols, findings, and conclusions of the studies. The final establishment of the shelf life and working shelf life should be agreed upon and signed off on by the experts involved; and
  • Having a defined template for conducting these studies makes setting them up easy and helps ensure no areas are overlooked.

Rumpf is technical manager of food programs for Shuster Laboratories, Inc. (Canton, Mass.), a Specialized Technology Resources, Inc. company. Reach him at arthur.rumpf@



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