Raw or processed food products deteriorate during processing, distribution and storage. Unless it is sterile, such products will contain indigenous microflora and, in some cases, foodborne pathogens. Unfortunately, presence and growth of microorganisms or foodborne pathogens are not always differentiated by the quality changes in the product. To help assure product safety and quality, microbiological shelf-life and challenge studies are essential R&D tools for food processors and manufacturers.
Explore this issueDecember/January 2007
Factors Affecting Product Shelf-life
Many factors influence shelf-life of food products. The shelf-life of food products is dependent on the interactive effects of intrinsic parameters (e.g. pH, water activity and preservatives) and extrinsic parameters (e.g. storage temperature, humidity level and gaseous environment), as well as the raw material quality and sanitary conditions applied during manufacturing. Microbiological and chemical changes, and physical deterioration during storage determine the shelf-life of a product. Microbiological changes occur as a result of microbiological growth of indigenous microflora. Chemical changes occur as a result of chemical reactions such as enzymatic degradation, non-enzymatic reactions and oxidation.
A complete shelf-life study is composed of microbiological, chemical and sensory evaluations, and determines the parameter that indicates the end of shelf-life. Shelf-life is defined as the period of time during which the quality of a food product remains acceptable for consumer consumption. At the end of shelf-life, the fresh quality of the food product is unacceptable or undesirable due to changes in taste, texture, aroma, color and appearance. Organoleptic qualities of the food begin to change as the spoilage bacteria, yeast or mold in the food grow. End of microbiological shelf-life may be determined based microbial counts. The number of organisms required to cause spoilage varies with the type of the organisms. Generally, however, it is accepted that 10 million bacteria per gram, 100,000 yeast per gram, or visible mold indicates the end of microbiological shelf-life.
A well-designed shelf-life study provides vital information on the microbiological, chemical and organoleptic changes in a product formulation during product storage. Shelf-life studies should be uniquely designed for each product. A number of variables must be considered when designing a shelf-life study. Storage temperature, relative humidity, types of analyses (i.e. microbiological, chemical or organoleptic analyses), method of analyses, sampling method, number of replications and duration of the study are some of these variables.
Critical Information Through Challenge Studies
In a challenge study, the stability of a product is determined against spoilage organisms or foodborne pathogens. If the count of the challenge organism does not increase during shelf-life storage, the product formulation is considered microbiologically stable against the challenge organism. Microbiologists define the increase as a 1-log (10 fold) increase in the count of the challenge organism.
A well-designed challenge study provides critical information on the microbiological stability of a product formulation against spoilage organisms or foodborne pathogens. Microbiological challenge studies also play an important role in determining whether a specific process is in compliance with the predetermined performance standards.
When conducting a microbiological challenge study, it is important to consider the key factors such as pH, water activity and preservative level that influence microbiological growth. These factors may be key in determining the stability of the product against challenge organisms during storage. Failure to consider the specific product parameters and environmental factors could result in faulty conclusions. Each key factor in the product formulation must be tested solely or in combination under worst-case conditions during its intended shelf-life. For example, the product must be challenged on the high side of the pH tolerance range. Conversely, the product must be challenged on the low side of preservatives within the tolerance range.
Water activity, temperature, gaseous environment and presence of antimicrobial compounds have a profound effect on the microbiological growth. These parameters are set at the time of product development. Changes in these parameters determine the shelf-life, and the microbiological stability and safety of the product.