The normalized yellowness had a quasi-linear ascendingtrend with the product moisture content due to the brown pig-ments formation by prompting the Maillard reaction as dryingprocess continued. Krokida et al. (2001) and Fernandez et al.(2005) found that the yellowness increased with progressingdrying time and reducing moisture content during convec-tive drying of apple slices. It could be related to the volumeshrinkage, causing an increase in the carotenoids concen-tration through the apple slices and thus shifting the colortoward the yellowish region. It is also obvious from Fig. 5that the normalized yellowness was significantly higher fordrying air temperature of 60◦C than the drying air temper-atures of 50 and 70◦C. It might be presumably attributedto the continuous reduction of -carotene at the tempera-ture around 60◦C due to the activation of lipoxygenase andperoxidase enzymes, as previously stated. This in turn ori-ented the apple slices color from the reddish zone to theyellowish