Determining the shelf–life of food products - Part 4

6. When a ‘use-by’ date is required for safety reasons6.1 There may be a food safety concernA ‘use by’ date is required for safety reasons where a food could become unsafe during its shelf life. The formation of toxic substances or the growth of pathogenic microorganisms may not provide visible signs that the product could have become unsafe to eat.
It is relatively uncommon for constituents of the food to breakdown or change so that toxic substances are formed, e.g. oxidation of fats and oils. The potential for this to occur will usually be mitigated by:

•  the addition of substances that reduce the potential for the changes to occur, e.g. antioxidants;
•  packaging to reduce exposure to light which may cause changes; and
•  storage instructions, e.g. refrigerate or store in a dark space.

However if the potential remains for toxicity to develop, a ‘use-by’ date is required for a safety reason.
Modern technological improvements to food processing, ingredients, packaging and storage has decreased the potential for chemical toxicity developing in the food. A greater diversity of foods with a prolonged chilled storage has increased the potential for pathogenic bacteria to be present. This will mean that the use and validation of ‘use-by’ date marking has become very important.
Before the start of refrigerated storage and modern food technology, foods were preserved using processes such as drying, salting, pickling and fermentation, either on their own or in combination. These foods could be stored at room temperature for long periods. As well as the food being preserved, pathogenic microorganisms would usually be inhibited from growing and they would die off over time. Today milder forms of processing are preferred, so that foods are not as dry, salty or acidic. This often produces a product that is more acceptable to consumers, but these products will have a shorter shelf life than the traditional product. Chilled storage and special packaging can be used to restrict the growth of pathogens and spoilage bacteria during storage, e.g. gas flushing, vacuum packing, etc. but this does not always result in an extended shelf life. This is because the storage conditions may actually favour the growth of some microorganisms’, e.g. cold-tolerant
spoilage and pathogenic microorganisms and those that thrive in the absence of oxygen.

Home produced foods, e.g. dips and sauces, are normally consumed within hours of being made. However when these are produced commercially, they will need an extended shelf life, usually several weeks in length. Extending the shelf life may be achieved by a combination of factors relating to the formulation of the food, type of processing applied and the use of refrigerated storage. However these may not be sufficient to prevent the survival and growth of any pathogenic bacteria present and so it may be necessary to:

• reformulate or package the food so that growth cannot occur;
• ensure that there are no pathogenic bacteria present, e.g. treat the product in its final packaging;
• reduce the shelf life so there is less time for pathogens to grow to unsafe levels;
• reduce the potential for pathogens to survive by increasing the severity of processing, e.g. replace
• pasteurisation with UHT; or
• adopt more rigorous ingredient specifications 

Figure : Decision tree: Applying a ‘use-by’ date for safety issues