Application of a thin-layer equation to drying data of fresh and semi-dried fruits

A thin-layer model, such as the Page equation, was applied to air drying da ta of high sugar-containing agricultural plant products, such as currants, sultanas, figs and plums. A good linear relationship was found and the two parameters of the Page equation were evaluated. The drying kinetics was eva luated for fresh material as well as for dried fruits. The Page equation wa s successful for the modelling of drying fresh fruits; it failed to predict the drying behaviour when the drying was continued for moisture contents b elow 15% (d.b.), which is the water content usually required to attain shel f stability of dried fruits. This was attributed to the Page equation being accurate only in cases where weight reduction is mainly due to water evapo ration. Deviation from the Page equation occurs where there is a further re duction in weight due to the decomposition of sugars at relatively high dry ing temperatures and moisture contents lower than that typical of dried fru its (below 15% d.b.). (C) 1999 Silsoe Research Institute.