Mathematical modelling of the drying curves of kiwi fruits:: influence of the ripening stage

The drying behaviour of kiwi fruits at different stage of ripeness has been evaluated. A diffusional model solved by a finite difference method has been proposed to simulate the drying kinetics at different temperatures. Drying curves of ripe kiwis exhibited only one diffusional period, whereas two different diffusional periods could be observed on the drying curves of green and half-ripe kiwis. Furthermore, the drying curves of green and half-ripe kiwis were coincident. The effective diffusional coefficient, which was identified at different temperatures (from 40 to 80degreesC from experimental data, varied with temperature according to the Arrhenius equation. An adequate simulation of the drying curves using the proposed model was achieved. Thus, the percentage of explained variance for the drying curves of green and half-ripe kiwis (considering two diffusional periods) was 99.7 and 99.3% for the ripe kiwis (only one diffusional period). Regarding to the characteristics of the dried kiwis, it was observed that the colour of the samples was mainly affected by the drying temperature, whereas functional properties such as hydration and fat retention capacities were mostly influenced by the stage of ripeness of the fruit. (C) 2004 Society of Chemical Industry.