This project, ‘Additive-free treatments for shelf life extension of minimally processed foods’, is being led by Dr Robert Hancock with Paul Walker as project staff.

Minimally processed foods (for example, bagged salads and prepared vegetables) have become increasingly popular over the last decade. They represent a convenient way in which consumers can help to achieve the recommended five portions of fruit and vegetables per day.

As minimally processed foods are living plant tissues, food preparation invariably leads to a steady decline in product quality with loss of visual appeal, decreased nutritional content and increased microbial growth as the product approaches the end of its shelf life.

Currently manufacturers use a number of techniques to maximise product shelf life including the use of chlorine based washes, the addition of acidulants and antioxidants and packaging the products in a protective modified atmosphere.

Both consumers and regulators are becoming increasingly uneasy about the addition of chemical protectants to increase shelf life and it is likely that increased legislation will limit the use of some commonly used compounds in the future. For example, the use of sulphites is coming under increased regulatory scrutiny as a result of their implication in the development of allergies.

Alternative methods

There is less opposition to the modified atmosphere alternative, however the costs of installing modified atmosphere equipment is high, there are potential hazards associated with having pressurised gasses on site (particularly oxygen) and the response of different products to the same atmospheric modifications are unpredictable.

In recent years, it has become apparent that challenge of plant materials with one sub-lethal stress appears to protect against other future stresses and this observation has been used by researchers and food processors to develop benign methodologies for the extension of shelf life in plant products.

Treatment with low doses of UV light has been shown to effectively extend shelf life in both fruits (for example, melon¹) and vegetables (for example, broccoli²) and mild thermal treatments (heat stress) have been widely used to try and develop methods for shelf life extension in a broad range of commodities³.

Although these techniques are widely accepted by consumers and regulators and despite the low costs of inclusion into processing lines, uptake has been low as a result of the need to recalibrate the technique for each product.

The aim of the current project is to examine the underlying mechanisms of protection and develop markers that can be used to rationally transfer the technique between products. The development of such markers will allow the rapid uptake of thermal treatments across the fresh-cut sector providing market advantage to producers and convenient, nutritious and safe minimally prepared vegetables for consumers encouraging wider consumption.

The project is being funded by the Scottish Enterprise Proof of Concept Fund.

References

1. Beaulieu, J.C. 2007. Effect of UV irradiation on cut cantaloupe: terpenoids and esters. Journal of Food Science 72, S272-S281.

2. Lemoine, M.L., Civello, P.M., Martínez, G.A. Chaves, A.R. 2007. Influence of postharvest UV-C treatment on refrigerated storage of minimally processed broccoli (Brassica oleraceae var. Italica). Journal of the Science of Food and Agriculture 87, 1132-1139.

3. Artes, F. and Allende, A. 2005. Processing lines and alternative preservation techniques to prolong the shelf life of fresh minimally processed leafy vegetables. European Journal of Horticultural Science 70, 231-245.