Shelf Life Study: Understanding the Basics

‘Food safety and quality’ awareness is increasing with consumers. As a conscious buyer nobody would like to buy a food product that has passed its ‘Best Before’ date fearing that the product might have become rancid, stale or a food safety hazard. A best before date helps the consumer to select a product with acceptable quality. Declaration of ‘Best Before’ date on all packed food items is a mandatory requirement for all food producers, manufacturers and retailers.

How to decide ‘Best Before’ date of a food product?

Best before date of a food product can be determined by carrying out what is called as ‘Shelf life study’ of the product. A shelf life study is an objective means to determine how long a food product can reasonably be stored and used, without any appreciable change in quality. A product that has passed its shelf life might still be safe, but quality can no longer be guaranteed. The shelf life of a product begins from the time the food is prepared or manufactured. The responsibility of carrying out shelf life study entirely lies with the food producer/manufacturer. Shelf life studies are beneficial to producers since it gives the food producers an insight into their formulation and processing variables.

A methodical shelf life study can certainly benefit the manufacturers in terms of packaging improvements, additive additions or any other process developments that would help their product to retain its quality over a longer period of time.

What affects shelf life of food products?

Factors affecting the shelf life of a product include following:

• Water activity, pH and initial microbial load of the product
• Increase in temperature, moisture/humidity and light of the storage environment
• Improper storage and handling conditions
• Inappropriate packaging material of the product

These factors eventually lead to either microbial or non microbial spoilage.

Microbial Spoilage: Microbial growth at higher humidity and temperature is fast. Growth of yeast, molds, and bacteria may lead to food spoilage or in some cases even poisoning. The time required for microbial growth and subsequent food spoilage depends on temperature and storage conditions of the product, handling conditions and packaging material of the product. Microbial spoilage due to pathogenic organisms also needs to be considered.

Non microbial spoilage: Light induced change can cause rancidity, vitamin loss or color loss of the product. Increase in temperature can cause the product to lose its nutrients, flavor/aroma or consistency. Some packaging materials like paper bags are permeable to gases, water vapor etc. which may lead to oxidation of the product.

 How to carry out Shelf-life studies?

Shelf life study is carried out by two methods:

Real Time Method: This is a direct method and involves storing the product under preselected or ideal conditions for a period of time more than the expected shelf life of the product. In reality however, once the product reaches the end user, it may get tampered or may not be stored under the recommended conditions. This may accelerate the spoilage. Thus, the shelf life estimated by real time study should still allow a ‘safe’ margin for the product to compensate for the tampering that the product may have to undergo.

Accelerated Study: This is an indirect method and attempts to predict the shelf life of a product without running a full length real time storage study. This kind of study is useful especially for new products and products having a long shelf life. The method involves storing the product under accelerated storage conditions like high temperature, agitation and humidity. As a result the end of shelf life is achieved quickly and the product is ready for sale in a relatively short period.
The results obtained from the accelerated studies are extrapolated to get the real time shelf life. It has been proven that accelerated studies may under-predict or over-predict the real shelf life. Therefore  such studies are not currently accepted by regulators without considerable consultation.  Additionally the costs of data analysis for a complex matrix can make an accelerated study a very expensive research project.

During shelf life studies the product is tested at periodic intervals to check when the spoilage begins. It is advisable to make a neat calendar schedule of the shelf life study plan with the sampling carried out at the beginning (zero day), at the end and between regular intervals.

How to decide the sampling intervals?

The sampling interval should typically be 20% of the expected or estimated shelf life.

 How often one needs to do shelf life study for a product?

As long as the composition and source of raw material, processing conditions and packaging materials remain unchanged, the study need not be repeated.

What test parameters should be chosen for shelf life study?

Selection of appropriate test parameters is very important and decides the success of shelf life study. For example, a bakery product like bread is susceptible to yeast growth and can lead to either surface spoilage or fermentative spoilage of the product depending on the water activity of the product. Thus, this product should to be tested for water activity and yeast during the shelf life study. Identification of any food poisoning organisms present is important for food safety. Tests required depend on the particular product. Microbiological standards and guidelines give guidance on the types of organisms and their number that can be considered acceptable, or unsafe, in a food.

Apart from  microbiological parameters, organoleptic properties or sensory evaluations of food can also be used to study the shelf life of a product.  Customer acceptance is largely dependent on flavor, color and texture of a product.

When to end the shelf life study of a product?

All food spoil with time, but there is a considerable variation in spoilage rates. Shelf life studies are unique and vary from product to product and manufacturer to manufacturer. When the quality of a product starts deteriorating it is reflected in its microbial, sensory, and physical evaluations and it is on these evaluations that one has to determine the end of shelf life study.