Consumers expect to purchase high-quality, fresh food, but recently, they’ve also begun to look for foods with fewer or no food additives or preservatives, pressuring manufacturers to reformulate products to meet growing clean label demands and to ensure food safety and brand protection. Manufacturers are also challenged with determining and maximizing the shelf life for products that are exposed to varying conditions in the supply chain. Shelf life touches on all the issues mentioned, and shelf-life determination is an essential requirement in providing safe, quality food products to consumers.
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What Is Shelf Life?
There are many definitions of shelf life provided by governments and organizations. The Institute of Food Science and Technology defines shelf life as “the period of time during which the food product will remain safe; be certain to retain its desired sensory, chemical, physical, microbiological, and functional characteristics; where appropriate, comply with any label declaration of nutrition data, when stored under the recommended conditions.” Both food safety and quality are important aspects of acceptable shelf life. Although pathogens are usually monitored during shelf-life studies, a suitable food safety program is the best way to ensure the product’s safety.
Factors Affecting Shelf Life
Both intrinsic and extrinsic factors influence the shelf life of food products.
Initial quality. For perishable food, the initial microbial load will influence the shelf life. Using ingredients that have already started to deteriorate (e.g. old oil) or overprocessing can result in loss of texture or nutrients (e.g. vitamin C).
Inherent nature of the product. Fresh or perishable foods have an inherently shorter shelf life than shelf-stable foods. The low water activity of a product such as rice makes it an inherently shelf-stable food, for example.
Product formulation. The addition of preservatives or antioxidants can extend the shelf life of the product. Formulation changes such as replacing the type of acid, removing nitrates from a processed meat, and reducing the amount of added salt can also change the shelf life of the product.
The following are extrinsic factors.
Packaging. For shelf-stable products, the barrier of the package can affect the shelf life. For example, moisture absorption for a cracker will affect the crispness of the product and a moisture barrier is required. If the product has a large fat component (e.g. potato chips), fat oxidation affects the shelf life and an oxygen barrier is required. Light protection may also be required. Without light protection, milk is susceptible to vitamin degradation and off-taste due to light-induced oxidation.
Transportation and storage conditions. Exposure of the product to variable temperatures and relative humidity in the supply chain (including the retail environment) can affect the shelf life of foods. For refrigerated products, higher-than-optimal temperature storage can accelerate microbial growth. Oxidation reactions are also accelerated by higher temperature exposure, thus shortening the shelf life of products.
Consumer handling. After purchase, transfer of food from the store to home can result in higher temperature exposure. Consumer refrigerators can also be at higher-than-optimal storage temperatures. Once the package is opened, the shelf-life date assigned by the food manufacturer is no longer applicable.
Understanding the End of Shelf Life
What constitutes the end of shelf life? The end point can be indicated from relevant food legislation, guidelines provided by government or professional organizations, or the use of acceptable industry practices. Often acceptability limits are chosen based on self-determined end points. For the most part, the food industry relies on sensory perception as an indicator of product failure. Product acceptability may be determined when there is a significant difference in the aging sample compared to a fresh sample by using discrimination testing (e.g. paired comparison, triangle, duo-trio, etc.). Descriptive analysis with expert panelists describes the change in sensory attributes (e.g. odor, taste, appearance, and texture) and can indicate consumer rejection. Although acceptance testing or use of consumer panels for acceptability can be more accurate, it is seldom used since a large number of panelists are required, resulting in a more time-consuming and expensive process.