After different drying procedures, the content of the enriched
apple parenchyma with quercetin glycosides by VIwas determined.
FD and MVD only slightly influenced the quercetin glycosides and
quercetin aglycone contents. The ratio between quercetin and the
glycosides remained constant during the process and corresponded
to the original ratio in the apple peel extract (Table 2). The corresponding
quercetin glycoside contents are detailed in Fig. 5, which
shows marginal but statistically significant degradation of quercetin-
3-O-galactoside and quercetin aglycone due to the MVD,
when compared with the freeze dried apples. Furthermore, the
successive air drying of apple slices at 50 C for 4 h e adjusted to
MVD before e did not influence the quercetin glycosides. In
contrast, AD procedure of VI apple slices resulted in marked quercetin
glycoside degradation. The sum of quercetin derivatives was
reduced to 44% in comparison to FD. The highest degradation was
detected for quercetin-3-O-xyloside (59%) and the aglycone
(54%). Thus, the degradation reaction of the monoglycosidic
quercetin derivatives induced no quercetin aglycone accumulation.