It must be noted that the normalized redness values of apple slices was inversely proportional to the actual redness. Since the apple slices redness magnitudes were commenced from negative values due to apple slices greenness and its sign maintained constant during dry-ing. Generally, the redness values of apple slices at drying airtemperature of 60◦C were lower than the drying air tempera-tures of 50 and 70◦C. It could be related to the promotion of theMaillard reaction at drying air temperatures of 50 and 70◦C, aspreviously elucidated for the normalized lightness. It can bealso inferred that the drying duration had a profound effect onthe progression of the Maillard reaction over the effect inten-sive drying air condition. In addition, the -carotene contentof apple slices was continuously decreased at drying tempera-ture of 60◦C, since the lipoxygenase and peroxidase enzymeswere stimulated at a temperature around 60◦C and degradedthe available carotenoid (Suvarnakuta et al., 2005). As well,it has been stated that the carotenoid concentration is sig-nificantly responsible for the foodstuffs red color variationsduring thermal processing (Niamnuy et al., 2007; Contreraset al., 2008). However, the comparison between the rednessvalues of slices at drying air temperatures of 50 and 70◦Cshowed that the effect of the Maillard reaction on the red-ness values of apple slices predominated over the effect ofcarotenoid concentration. It is worth noting that the higherdrying air temperatures might lead to the higher volumeshrinkage. Moreover, the higher redness values of samplesat drying air temperature of 50◦C compared to the drying airtemperature of 70◦C might possibly resulted from the higher amount of brown pigment formation due to the longer dryingduration, as previously represented for lightness.