Packaging is the most critical factor for the quality of fresh-cut fruits and vegetables. It is also the most difficult factor to control. Scientists investigate how fresh-cut products keep taste and freshness after processing.

Snack-carrots gasp for air, apple slices get brown and sugar peas go sour. That is the way it goes if fresh fruit and vegetables are not packaged properly. Scientists at the University of Aarhus intend to do something about it.

They are investigating the critical points of the production chain and what happens to the products’ quality, taste and health-promoting properties when fresh fruits and vegetables are prepared. The aim is to make it possible to produce prepared or half-prepared products that taste like homemade.

- Prepared fruit and vegetables that make life easier for the consumer – convenience products – are living products that breathe, says senior scientist Merete Edelenbos from the Department of Food Science at the Faculty of Agricultural Sciences (DJF) at the University of Aarhus.

- Packaging of the products and the atmosphere around them is therefore very important, she says.

Eating your greens is hard work

For a consumer it can be backbreaking work to eat six pieces of fresh fruit and vegetables a day. One has to drag home no less than 24 kg each week for a family of four. Fruit and vegetables easily lose 30 per cent waste in the shape of peels, pits and leaves, and take up a lot of room in the shopping trolley, the refrigerator and on the compost heap. Besides that, it is hard work to rinse, scrub, peel, and cut fresh fruit and vegetables – and to carry out 6-8 kg organic garbage.

Just imagine how big the pile of waste is if you prepare a meal consisting of lime and avocado for starters, cauliflower and potatoes for the main course, and pineapple and oranges for dessert. No wonder the modern, busy consumer prefers buying fresh fruit and vegetables that are already washed and cut into smaller pieces: convenience products. A family of four then only needs to put 16 kg in the shopping cart each week.

The quality of convenience products must, however, be tip-top and they must taste as if they had just been prepared. That requires optimum processing and packaging.

- Packaging is the most critical factor for the quality of fresh-cut fruit and vegetables – both the most important and the most difficult, Merete Edelenbos points out.

Fruit and veggies need air

When you package fresh fruit and vegetables in film without macro holes you gradually alter the composition of the air in the package so it contains less oxygen and more carbon dioxide compared to air. This increases storage life. However, the fruit or vegetable breathes and if there is not enough oxygen coming into the package the product will choke, change taste and turn sour. Quality will go down. How much the product breathes depends on how it is treated before packaging and how it is stored after packaging. Handling alone increases respiration; the oxygen requirement and expiration of carbon dioxide increase.

If the packaging material is too airtight the vegetable cannot breathe. Therefore, the scientists are collaborating with the industry to develop packaging solutions that alter the permeability of the packaging material, such as by making holes in the bag.

- Every vegetable has different requirements and the requirements also depend on whether the vegetable is peeled, cut or grated. It is therefore imperative that the packaging solutions are adapted to each individual product. The industry must prioritise processing and packaging technology so that the balance between oxygen and carbon dioxide is satisfactory, says Merete Edelenbos.

Quality treatment from field to fork

Correct packaging is not enough. Fresh fruit or vegetables must also be handled gently, correctly and quickly throughout the whole process.

The peeling process must be gentle and the cutting process must ensure a smooth cut surface by either changing or whetting the knives correctly and in time. During the whole process the products must be properly cooled since a higher temperature increases respiration. The products should naturally be cleaned, but they must not soak after cutting since the water will remove taste and vitamins.

- Our studies show that there can be marked differences in end-quality even if the raw material quality comes from the same batch. That means that product preparation has a significant impact on final product quality, says Merete Edelenbos,

After packaging, product turnover must be quick to ensure top-quality products to consumers. This requires tight logistics, short distances and a reasonably large consumer population.

For more information please contact: Senior scientist Merete Edelenbos, Department of Food Science, Faculty of Agricultural Sciences, University of Aarhus, telephone: +45 8999 3406, e-mail: Merete.Edelenbos@agrsci.dk

Text and photo: Janne Hansen