Technical Talk – June 2011

All food manufacturers are trying to increase the shelf life of their
products. This is becoming increasingly important in an era of global
trade. In addition, consumers do not purchase foods on a daily basis, so
products need to last longer. 

A little knowledge goes a long way in lengthening product shelf life

All food manufacturers are trying to increase the shelf life of their products. This is becoming increasingly important in an era of global trade. In addition, consumers do not purchase foods on a daily basis, so products need to last longer. 
The shelf life of food is the period from the start of production until spoiling of the product renders it unsafe to eat or of a quality that is unacceptable to the consumer. 

The two main concerns are food safety and quality. Changes during storage can be attributed to the growth of micro-organisms. Micro-organisms may affect shelf life in two ways. If storage conditions are favourable, pathogenic bacteria will proliferate, contaminating the food. Spoilage micro-organisms will also grow in food, causing additional quality issues. There are several food processing parameters and conditions that are required in order to prevent or slow the growth of these micro-organisms. Applying appropriate heat to the food during processing (pasteurization) will eliminate most pathogens; however, it won’t eliminate all micro-organisms. Some pathogens, such as spore formers, require much harsher temperatures for sterilization or retorting in order to be eliminated. Sterilization will eliminate all micro-organisms and if the product is packaged appropriately, it will have a long microbial shelf life.

The pH of the food also plays an important role. A low pH (high acidity) will keep pathogens in check; however, many spoilage microbes will multiply under these conditions. Another factor to consider is the temperature of storage. Refrigeration will help control pathogens, but again, many other microbes will continue to grow, albeit at a lower growth rate.

Packaging also plays a critical role. Packaging’s main role is to prevent oxygen presence. This restricts the breeding of aerobic micro-organisms, reducing both pathogens and spoilage micro-organisms. To address these issues, new packaging materials that incorporate antimicrobial nanoparticles or agents to eliminate oxygen are emerging. These materials are more effective in extending microbial shelf life. However, it is important to understand that eliminating oxygen may encourage the growth of anaerobic pathogens such as Clostridium botulinum. When you are dealing with foods that are prone to contamination with anaerobic pathogens, you must also impose other controls, such as refrigeration or antimicrobials.

Eliminating or slowing the growth of pathogenic and spoilage micro-organisms will not solve all shelf-life problems. Changes in the texture, flavour and appearance, as well as other food characteristics, also play a key role in shelf life. Although food safety is paramount, taste and appearance is very important to the consumer. Health is also a major driver of new food product development. Mono and polyunsaturated fats, such as omega oils, are currently used in many products due to their health benefits. These oils have a very short shelf life; they oxidize and become rancid. To extend the shelf life of products made with omega oils, antioxidants are often added to extend the shelf life. In order to prevent oxidation, some omega oils can be microencapsulated. This can serve dual purposes, extending shelf life and eliminating the fishy taste that is often associated with omega-rich oils. Using modified atmosphere packaging can also prevent oxidation by eliminating oxygen from the packaged product.

To deliver health benefits to the consumer, the active components of a food must be viable through production until the end of the product’s shelf life. It is therefore important that the processes are gentle enough not to destroy any active components while still being effective in keeping pathogens in check. Effective gentle processing technologies have been developed to replace harsher traditional ones. 

Changes in the texture of foods also play a very important role in their shelf life. We in the baking industry are very familiar with these changes, particularly in terms of staling. Staling in bread is the result of many undesirable changes that occur during storage, including toughening of the crust and firming of the crumb. These changes result from a loss of moisture and the retrogradation (or recrystallization) of the starch in combination with its association with the gluten matrix. This effect is accelerated at refrigeration temperatures but can be reversed with heating or toasting. Many factors are known to decrease the rate of staling in bread and thus extend its shelf life. The addition of surfactants will result in a complex with amylose (a starch component), producing a softer bread with a longer shelf life. Adding shortening will have a similar effect. Recent developments in the extension of bread shelf life involve specific amylase enzymes that are readily available and effective.  

Extending the shelf life of a food product may involve adding ingredients, modifying production processes or applying new technologies. Because of the multiple factors impacting the shelf life of food products, a single change or new technology may not be sufficient to achieve a longer shelf life.

When selecting an ingredient or technology to extend the shelf life of a food product, one should also take into account its regulatory status in the country of production and any other countries in which the product will
be sold.

For more information or fee-for-service help with product or process development needs, please contact John Michaelides at GFTC at 519-821-1246 ext. 5052, by fax at 519-836-1281, or by e-mail at jmichaelides@gftc.ca or j.jmichaelides@gmail.com.