The shelf-life problem

SHELF-LIFE extension is the holy grail for the fruit and vegetable industry. A huge amount of food is wasted as it goes off before it is eaten. 

The supermarkets throw loads away every day. Consumers do the same. If we can add a few more days to the shelf life, we could reduce the amount of food waste and significantly reduce costs. We can also make it more likely that the consumer will get a quality product in good condition.

Fruit and vegetable processors can also reduce costs by extending shelf-life. At the moment, they have to pick their crops quickly and ship them by the fastest route possible. This is expensive and labour intensive. Additional shelf-life allows them to plan their labour usage better (avoiding expensive weekends for example) and ship using lower cost transport.

This particularly applies for international export business. Fruit and vegetables are shipped all around the world. Many are grown in the hotter parts of the world (Spain, North Africa, Turkey, the Middle East, South and Central America for example) and shipped to the UK, Northern Europe, Russia, the US and elsewhere for consumption. Due to limited shelf life, many of these products have only a few days left when they arrive at their destination. Some cannot be shipped at all, it is a waste of time they will have degraded before they arrive. Others have to be shipped by air. This is ruinously expensive for low value products like vegetables.

There are several advantages to extending shelf-life:

•Improves the quality, taste and texture of the food for the consumer

•Reduces food waste and associated costs

•Reduces processing and shipping costs

•Brings new export markets within range of population centres

Packaging can have a negative or positive effect on the shelf life. Unpackaged vegetables will dry out. The same thing happens if they are packed in paper or other permeable package. However, if they are  wrapped in most types of plastic film they can get soggy and slimy. Condensation and excess water inside the pack causes the food to rot. Bacteria and mould grow in the liquid and this becomes the main process of degradation. 

It is not just a question of humidity control. Fruit and vegetables ‘respire’ after they are packed; they absorb oxygen (O2) and release carbon dioxide (CO2). As a result, the O2 concentration in the pack tends to reduce and the CO2 level to increase. Low oxygen can cause the growth of some nasty bacteria which degrade the food very quickly (and can be dangerous in some cases). Excess CO2 can increase the acidity of the food which affects the taste and texture of the food. As such, it is important to allow O2 and CO2 to permeate in and out of the pack to maintain a balance. The ideal atmosphere is about 15% CO2 and 15% O2 - difficult to achieve in most cases. 

They key to shelf-life is to find a material which balances the O2 and CO2 permeability and the moisture vapour humidity to optimise the environment in the pack to give the maximum shelf life. This is a difficult balance. If the moisture vapour permeability is too high, the food will dry out. If it is too low, condensation will form on the inside of the pack (known as ‘fogging’) and the food will become slimy and mould and bacteria growth is encouraged. At the same time the O2 and CO2 permeability needs to be high enough to allow the pack to breathe while providing enough barrier to hold some of the CO2 in the pack.

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