Shelf-life

No matter how effectively Modified Atmosphere technology is applied to food, no product can remain on the supermarket shelf indefinitely. Over time, food spoilage inevitably sets in and the rate at which it occurs depends on the physical structure and properties of the food itself, the type of micro-organisms present and the environment the food is kept in. The acidity of food, its respiration rate, nutrient content, natural resistance to micro-organisms and its biological structure are among the factors which affect the rate of decay.

What is shelf-life

The shelf-life of a product is the time after production during which it remains acceptable for consumption. The end of the shelf-life is, therefore, the point at which it becomes unacceptable.

• Remain safe
• Be certain to retain desired sensory, chemical, physical and
  microbiological characteristics
• Comply with any label declaration of nutritional data when
  stored and handled under the recommended condition

What influences shelf-life?

The shelf-life will be influenced by many aspects of Good Manufacturing Practice and product formulation, e.g. pH (acidity), salt level or water activity and preservatives. Combinations of these factors are often used together to achieve stability, known as hurdle technology.

• Raw materials
• Product formulation
• Processing
• Packaging, including gas atmosphere
• Hygiene
• Distribution
• Storage
• Consumer handling

These factors exert their effects on microbiological, chemical and physical parameters within the food, which often result in a loss of sensory quality. The point at which these effects influence the product, such that the change becomes noticeable or the product unacceptable, is the end-point. It is the time taken to reach the end-point that has to be determined when assessing product shelf-life. The packaging format often has a significant influence on the acceptable, durable life of chilled foods. Consideration needs to be given, particularly to products designed as multi-portion or bulk commodity packs, to the effect of opening the pack on product durability. It may be necessary to qualify any shelf-life coding (Use By/Best Before) with clear instructions on the packaging limiting the time available from opening to consumption and indicating, where necessary, any specific handling instructions to the consumer.

End of shelf-life

For most perishable chilled food products, the end-point will depend on a number of factors. In some cases, the end-point may be defined by levels of micro-organisms present based on recommended guidance (PHLS, 2000; IFST, 1999). In other cases, the end of life may be determined by sensory or biochemical deterioration. The emphasis on the specific end-point criteria will vary between different products and must be defined during the shelf-life evaluation process.

Shelf-life testing methods

There are a number of methods for determining the shelf-life of different food products including microbiological, chemical and by sensory evaluation. Different factors will affect the end of shelf-life depending on the product, packaging and conditions surrounding the product. Shelf-life testing can be carried out during development and pilot scale production of the product but should always be carried out once full scale production has been reached.

Microbiological testing

The type of product and gas mixture used will influence the growth of specific groups of micro-organisms. Packing in an oxygen free environment will allow anaerobic organisms to grow whereas products packed in the presence of oxygen will permit the growth of aerobic micro-organisms. Sampling should be carried out regularly during shelf-life testing on a minimum of three to five samples per sampling date per pack format.

Biochemical testing

Colorimeters can be used to measure colour changes with different food products. A colorimeter may pick up slight changes not noticed by the human eye. Chromatography can be used to measure changes of the volatile compounds in the food product during storage. Changes in nutritional content can be measured during shelf-life to determine if there are any significant changes.

Sensory evaluation

There are a number of different formats for carrying out sensory evaluation on products. The product can be assessed for appearance, odour, texture and flavour to determine end of shelf-life. Specific individual attributes of the product such as ripeness, degree of fermentation, juiciness, strength, acidity and moistness can be observed by trained sensory assessors.

back to Food Spoilage