| Sorption isotherms and state diagrams (ice melting and glass transition curves) of strawberry, kiwi and different model solutions with similar composition were obtained and modelled. These are useful tools for description of system development in drying and freezing processes. In strawberry experimental conditions (entire or homogenised tissue and sorption or desorption way) had a significant effect on the obtained relationships. Likewise, the effect of partial dehydration of fruits, freezing rate and frozen storage time on fruit quality was analysed. Tested freezing rate ranged between 0.1 and 4°C/min. Dehydration treatments (only in strawberry) were air drying at 45°C and osmotic dehydration with 65° Brix sucrose solution at 30°C. These were applied independently or in combination until samples reached three different moisture levels (between 73 and 83%). Changes in sample composition, volume, colour and mechanical and structural properties were evaluated as quality parameters.;Freezing rate notably affected sample drip loss and colour in kiwi fruit, but no significant effects were observed in strawberry directly frozen or partially dehydrated. Dehydration pretreatments provoked changes in composition, colour and mechanical properties, depending on the kind of treatment and dehydration level. Nevertheless, after freezing-thawing, dehydrated samples maintained quality properties better than directly frozen fresh strawberries. Air drying showed the best cryoprotectant action, especially when sample moisture was the lowest. This protection was observable through the minor changes in sample microstructure, mechanical properties and colour. Frozen storage time had small influence in the evaluated parameters in the controlled range. |
