Drying of pineapple slices in natura and pre-osmodehydrated in inverted sugar

Abstract

This research describes the drying kinetics and compares the convective drying rates of in natura and osmodehydrated pineapple slices in inverted sugar. The effective moisture diffusivity during air drying was estimated using Fick's second law of diffusion. The suitability of a theoretical liquid-diffusion model and seven semi-theoretical mathematical models for use in describing the experimental drying curves was also evaluated. Goodness of fit between experimental and predicted values was based on the root mean square error, mean absolute percentage error, mean bias error, agreement index, residual plot analysis and the principle of parsimony. Osmotic dehydration was conducted in 155, 310, and 465 mL L^-1 osmotic solutions, at 40 and 50 ºC for 2 h at 60 rpm. Convective drying was performed in a tray cabinet dryer using heated ambient air at 60 ºC and 1.15 m s^-1. Osmotic pretreatment facilitated water removal during the first hours of drying, a trend that was reversed towards the end of the process for samples osmodehydrated at the highest solution concentration. The effect of the osmotic pretreatments on drying rate was negligible at 40 °C, but at 50 °C the rate of moisture removal was more intense for samples in natura and osmodehydrated at the lowest solution concentration. Effective moisture diffusivity increased with temperature and solution concentration. The single-exponential, three-parameter semi-theoretical drying model gave the best predictions of the drying curves of pineapple slices both in natura and pre-osmodehydrated in inverted sugar.