Effects of drying and pretreatment on the nutritional and functional quality of raisins

The close relationship between the consumption of fruits and health status stems from the nutritional and non-nutritional compounds found in fruits which play a key role in the prevention of different diseases. However, fruit processing and storage greatly affect fruit compounds. The aim of the present work was to study the influence of processing on the stability of macro and micronutrients present in grapes, with a view to recommending products that provide the highest nutritional quality and the best health conditions. The study focused on fruit dehydration treatments. Conventional and microwave-assisted air-drying processes were used to obtain raisins. Dehydration caused a decrease of all grape compounds studied excluding total phenols. Moreover, compared to conventional processing, microwave-assisted drying produced greater losses of ascorbic acid in the grape and increased pectin solubilization with a consequent change in texture. However the microwave-dehydrated samples showed higher antioxidant activity.

► Microwave technique (with NaOH pretreatment) supposes an important reduction in the process time when compared to hot air drying.
► Microwave treatment affected the loss of ascorbic acid and minerals but increased total phenols availability and antioxidant activity.
► The use of microwaves could be recommended to obtain raisins.