Refratance Window 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 65oC, 75oC, and 85oC. 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 (27oC). 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 65oC, 75oC and 85oC and coefficient of determination ( R2 )
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 ( R2 )
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.
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