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Why do apple slices brown so easily?

2 August, 2004

Why do apple slices brown so easily?

Ever wondered whether the dried fruits you are eating still have any nutritional value? And why is it that apple slices brown so easily? Well you could soon have the answer thanks to a study being carried out by a University of Auckland engineering student.

Andy Ting, a final year Bachelor of Engineering student, is studying dehydration in foods as part of his final year research project.

Dehydration of food is an important aspect in the food processing industry with many fruits, such as apples, dried to provide a product that is easy to handle, store and use.

The Howick resident says fruit slices generally begin to change colour and dehydrate when exposed to heat and with apples the discolouring is more noticeable.

"But what I'm really interested in is not the apple slices that we eat at home, but the ones that are dried in food processing industries.

"Biological products such as apples often contain thermo-sensitive compounds, for example vitamins, which may be reduced or lost during drying. I aim to find a method of drying which minimises degradation in terms of food value, texture and colour," says Andy.

Research shows that the way fruits and vegetables are dried plays an important role in the nutritional value and appearance of the dried product.

In his study, Andy will use hot air flow to heat and dry apple slices. The study involves a series of experiments using a tray dryer rack connected to a heating device.

Apple slices will be placed on the aluminium rack, which has a glass top and bottom so that observations can easily be made. The heating device will then be used to supply a constant stream of hot air flow.

"The experiments will be carried out with variable temperatures and hot air flow rates. The whole set-up will be left to run for a long period of time and the differences in colour and weight of the slices will be recorded at certain intervals."

By the end of the experiment Andy intends to have sufficient data from which to make reasoned analyses on why discolouring occurs when drying and how this can be prevented.

Andy says storage after dehydration is also important in retaining the quality of the fruit and while he will not be studying this in his current research, it is an area he may consider exploring as part of postgraduate studies.

"I am quite fascinated by the food processing industry and would like to continue to work in this area. Natural disasters make us more aware of our dependence on fresh fruits and vegetables and I believe that the role of the food processing industry in trying to store fruits and vegetables long-term, with their nutritional values intact, will become more important."


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