Adsorption isotherm and heat of sorption of osmotically pretreated and air-dried pineapple slices.

Abstract

Slabs (1 �1.5 �5 cm) of pineapple were im- mersed in sucrose solutions of 52�B, 60�B and 68�B (w/w) at 25 �C for 12 h. Osmosed pineapple slices were subsequently air-dried at 60 �C for 72 h. Adsorption isotherms of osmo-dried pineapple slices were determined at 20 �C and 40 �C, using the gravimetric-static method. Isotherms were modeled using Brunnauer, Emmet and Teller (BET) and Guggenheim Anderson de Boer (GAB) models. Heat of moisture adsorptions were calculated from adsorption data using the Clausius-Clapeyron equa- tion. Adsorption isotherms of osmo-oven-dried pineapple followed the characteristic type III (J-shape) isotherms. Equilibrium moisture contents at constant water activity decreased with increasing temperature, but crossing of the isotherms occurred at aw~ 0.86. GAB and BET monolayer moisture decreased with increased temperature. The net isosteric heat increased with decreased moisture content, and decreased with increased sucrose pretreatment con- centration of pineapple slices.