Influence of osmotic dehydration conditions on apple air-drying kinetics and their quality characteristics

The influence of different osmotic pre-treatments on apple air-drying kinetics and their physical characteristics during drying were investigated. Apple samples were immersed in glucose or sucrose solutions of 30%, 45% (w/w) at different times. Sugar gain (SG) and water loss (WL) were calculated and an immersion time of 12 h was selected. Samples were further air-dried and the experimental data were fitted successfully using the Page model: MR = exp(−ktn). Porosity, compressive fracture stress and colour were measured. Apples osmosed in glucose showed a large moisture decline in the early drying periods and similar drying rates to untreated samples for the same moisture change. Osmosed apples in sucrose showed lower drying rates ascribed to sugars concentration on the outer layers of apple tissue and their crystallization during drying. Samples pre-treated in 45% sugar solutions had greater porosity and better colour retention during drying. In glucose osmosed samples a greater texture hardening rate was observed, in sucrose just the opposite occurred.