Multicriteria optimization of food processing combining soaking prior to air drying

A method for multicriteria optimization is illustrated by the example of apples processed by Dewatering and Impregnation Soaking (DIS) in concentrated aqueous sucrose solutions, and then air dried. The influence of the product history (modifications linked to DIS treatment) on its behaviour during drying process is assessed according to an experimental design. Five operating variables are taken into account: temperature, solution concentration and soaking time for DIS pre-step, and temperature and relative humidity for air drying. Results show a limiting effect of internal water transport by the sucrose impregnated superficial layer. This effect can be reduced by drying at high temperature (80 degrees C) On the other hand, the relative humidity of air has little influence on the behaviour of soaked materials. Multicriteria optimization takes into account six criterias and shows that stable and optimal quality products can be obtained at interesting energetic costs and for a short processing time duration (50 to 300 min).