Influence of osmotic dehydration pre-treatment on oven drying and freeze drying performance

- Optimisation of the osmotic dehydration operating parameters.
- Reduction of the processing times.
- Better retention of textural and structural properties.

Drying is largely used in food industry, since it allows prolonging the product shelf life by inhibiting microorganisms' growth and enzyme activity. Traditional drying techniques, such as air drying and freeze drying, suffer from several drawbacks, mainly long processing time, low rehydration capacity and change in food properties. Some pre-treatments, such as osmotic dehydration, can be applied prior to conventional techniques in order to produce an intermediate moisture product and, therefore, to improve the drying process. In this work, the influence of osmotic dehydration on oven drying and freeze drying performance was evaluated. Firstly, the effects of the main osmotic dehydration parameters were investigated in order to find the best conditions for water desorption. Secondly, experiments with oven drying, freeze drying and their combination with osmotic pre-treatment were carried out. Results of each technique in terms of final moisture content, water activity, rehydration ability, textural properties and microstructure were compared and discussed. It has been observed that the application of the pre-treatment allows reducing considerably the processing time and better retaining the food properties.