Abstract

Drying is an energy intensive unit operation and long drying periods tend to increase the energy requirements for the production of a unit dry product. In this study, the effect of blanching temperature - time combinations treatment conditions on the drying behavior of pineapple slices was investigated. Slices of pineapple were blanched at different temperature-time combinations before being dried in an oven dryer at a dry bulb temperature of 70oC. Four thin-layer drying models were fitted to the experimental drying data. The results show that drying rates and drying times were affected by the blanching temperature-time combinations. Drying times increased as blanching temperature-time combinations increased. The predominant drying regime of the blanched pineapple was observed to be in the falling rate period. The logarithmic model best describe the drying behaviour of blanched pineapple slices with goodness of fit ( > 0.99). The effective moisture diffusivity of blanched samples decreased with increase in blanching temperature-time combinations. This implied enhanced mass transfer activities of blanched pineapple slices at decreasing blanching temperature-time combinations. Therefore, blanching pretreatment at lower temperature-time combinations in the drying of fruits and vegetables reduces the drying time and energy cost of drying.

Key words: Blanching; drying; drying models; effective diffusivity; pineapple; temperature.