Influence of process setting in convective apple drying on selected parameters

Summary

In this work, the effect of two drying temperatures, three slice thicknesses and two apple varieties on the quality of apple slices dried in a convective dryer was studied. Selected quality parameters were evaluated. The results revealed that the three factors temperature, thickness and variety influence the individual quality parameters significantly to a different extent. Additional monitoring of an uncontrollable parameter, drying air humidity, allowed to investigate its effect on the drying process and the quality characteristics. The required drying time for apple slices to reach the target moisture 0.13 gw/gds is strongly influenced by the relative air humidity in the dryer (0) followed by the initial moisture content dry basis (E) and the thickness (B). The study of total colour difference (∆E) from apple slices was challenging nevertheless an impact of variety (C) and thickness (B) was determined. Those two variables affected the rehydration ratio noticeably as well. The investigation of relative volume (shrinkage) was also demanding and showed that again the relative air humidity in the dryer (D) and the initial IVIDI3 (E) have an influence on the shrinkage of apple slices. Water activity was found to be influenced mainly by the relative air humidity in the dryer (D), the drying temperature (A) and the interaction of those (AD). A small influence of the variety (C) was identified as well. Then again, statistical investigation of RR and aw should be viewed with caution as the collection of those data was done at different moisture contents at the respective ends of different drying times. The nature of these destructive measurements requires additional sampling or online moisture determination for future investigations.
The analysis of variance indicated that the models of responses are significant.