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).