Microwave-assisted hot air convective drying of whole cranberries subjected to various initial treatments

Abstract

The aims of study were to evaluate the effect of: (i) initial treatments such as sonication (S), convective freezing (F), sonication combined with freezing (SF), microwave-vacuum (MWV), microwave-vacuum combined with convective freezing (MWVF) and cryogenic freezing (N) as well as; (ii) replacement of hot air convective drying (HACD) with microwave vacuum drying (MWVD) in the final stage of drying on: the drying kinetics, average drying rates (DRAVG), the content of bioactive compounds and antioxidant activity of osmotically dehydrated whole cranberries. HACD of fruits took from 740 to 950 min. The use of microwaves instead of hot air in the final stage of drying (HACD + MWVD) reduced the drying time, which took from 80 to 493 min. DRAVG of HACD + MWVD was more than one order of magnitude larger than DRAVG of HACD. The use of microwaves during initial treatment and drying resulted in the shortest drying time, i.e. 20 min and the highest DRAVG, i.e. 0.092 kg H2O/kg DM/min. HACD + MWVD resulted in significantly higher contents of bioactive compounds and antioxidant activity of fruits than HACD. Among different pretreatments used in the present study, sonication and freezing (S, F, SF) gave the best results in terms of drying time and final product quality.