5. Conclusion This study showed that similar to freeze drying (FD), gentle microwave vacuum drying (MVD), of vacuum impregnated apple slices maintained high quercetin contents in the parenchyma. In contrast, air drying (AD) resulted in significant losses of quercetin derivatives and marked browning, indicating extensive oxidation reactions. Due to the moderate temperature regime (50 C max) during drying, strong structural changes occurred in MVD and AD apple slices. MVD apples slices showed slightly higher porosity than AD apple chips and both drying procedures resulted in high shrinkage. In contrast, FD apple slices showed significantly higher porosity and the lowest shrinkage.