Refratance WindowTM Dryer Dehydration Characterization of Cucumber (Cucumis Sativus) Slices at Different Temperatures

Abstract

Cucumber (Cucumis sativus) slices were dehydrated using a Refractance WindowTM dryer in which the flume water temperatures were varied at 65^oC, 75^oC, and 85^oC. The kinetic data obtained experimentally was fitted to 8 dehydration models categorized as empirical and semi-empirical models. The dehydration curves, the effective diffusivities and activation energy of the cucumber slices were estimated. Also, samples of the dried cucumber slices were rehydrated at room temperature (27^oC). The experimental rehydration data were used to construct the rehydration ratio plot. The values of the ascorbic acid content of the cucumber’s slices were also determined after experimentation for the process conditions studied. Observations indicated that the cucumber slices dried to a moisture content of 0.11 g-water/g-solid (dry basis) in about 40 to 115 minutes for the process conditions studied. The regression analysis results suggest that the Haghi and Ghanadzadeh thin layer model, best described the drying behavior for the 3.0 mm thick cucumber slices at 65^oC, 75^oC and 85^oC and coefficient of determination ( 2 R ) values of 0.9923, 0.9993 and 1.0000 respectively. The rehydration ratio of the cucumber samples increased to 5.25 in about 300 minutes after which the moisture content was about 11.50g-water/g-cucumber (92% wet basis). The rehydration data were also observed to fit a two-term exponential model with a coefficient of determination ( 2 R ) value of 0.9941. Finally, there was a decrease of 7.93 to 38.94% in the ascorbic acid content of the cucumber slices for the process conditions studied.