Influence of different drying methods on the quality of Japanese quince fruit

The aim of this study was to determine the effect of different drying methods - convective drying (at 50, 60, 70 degrees C), vacuum-microwave drying (at 120, 240, 480 W and 480 W with reduction to 120 W), a combination (of convective pre-drying (at 50, 60, 70 degrees C) and by vacuum-microwave finish drying (at 120 W)) and freeze-drying - on the quality factors of Japanese quince fruit, including phenolic compounds, antioxidant activity, and color. Drying kinetics were determined. The highest content of bioactive compounds was in samples after freeze-drying (total phenolic content - 57 g/kg dw; polymeric proanthocyanidins - 41 g/kg dw). The antioxidant activity measured by oxygen radical absorbance capacity (ORAC) assay was the highest for samples after vacuum-microwave drying at 480 W (0.8 mol Trolox/kg dw). Unfavorable changes in color, formation of hydroxymethylfurfural (HMF) and degradation of L-ascorbic acid as well as phenolic compounds were noted along with the increasing drying temperature and increasing magnetron power. The method that will ensure the proper appearance of dried fruits, storage stability and at the same time guarantee the retention of bioactive compounds seems to be freeze-drying.