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Mass transfer kinetics and optimisation of osmotic dehydration (OD) of fruits and vegetables with diverse structures were studied. Different concentrations of sucrose (20-60°Brix) and process times (0-24 h) were used. Magee's model was appropriate for predicting water loss (WL), while Azuara's model fitted well solids gain (SG) data and represented more accurately the evolution of the complete process close to equilibrium. Polynomial equations for each kinetic variable [WL, SG and weight reduction (WR) -for pumpkin, kiwi and pear] using multiple linear regression were fitted for a selected range of experimental data (30-240 min, 20-60°Brix). A complete solution algorithm for desirability function was coded in Matlab Ò 7.2 (Mathworks, Natick, MA, USA) with the aim to optimise osmotic dehydration process in terms of WL, SG and WR; optimal conditions were found for each fruit. Besides, an optimal common zone was identified for OD corresponding to process time from 114 to 240 min and sucrose concentration from 54 to 60°Brix.

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Osmotic dehydration (OD) process permits to improve the organoleptic characteristics of the products; nevertheless, depending of the product, the incorporation of great amounts of solute can be not desirable for consumers. The application of hydrogel coatings would contribute to overcome this inconvenient acting as a barrier to solute entering. An Alginate-Calcium Chloride barrier system (A-CC) was tested with or without pretreatment of Ca 2+ as a firmness agent applied to pumpkin sticks. Products were dehydrated in sucrose and glucose solutions (40 and 60 % w/w). Different parameters were estimated along the process such as soluble solids uptake, water content, weight reduction; besides, texture and microstructural changes were studied. The A-CC configuration complies with the barrier function to solids uptake from the dehydrating solution in case of 60% of sucrose, allowing water exit from the vegetal matrix. The pretreatment with Ca 2+ contributed to the retention of the product firmness. Integrity, adhesiveness and thickness of the A-CC system during the OD process were evaluated by ESEM. In this case, the coating thickness reduction was according to the product weight reduction, indicating that the coated product was dehydrated as an integrated system.

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