Microwave-vacuum-assisted drying of pretreated cranberries: Drying kinetics, bioactive compounds and antioxidant activity

Abstract

Abstract This study focused on the effects of microwave-vacuum-assisted drying on the drying kinetics, bioactive compounds and antioxidant activity of whole cranberries subjected to different pretreatments, i.e. sonication, sonication combined with convective freezing, microwave-vacuum pretreatment, microwave-vacuum pretreatment combined with convective freezing, convective freezing and cryogenic freezing. Compared to hot air convective drying, microwave-vacuum-assisted drying shortened the drying time by 54%. The application of microwaves in the final stage of drying allowed to obtain drying rates 17 times higher than in the convective initial stage. Berries dried by microwave-vacuum-assisted drying were characterized by higher contents of polyphenols (from 22.14\xa0±\xa00.49 to 27.51\xa0±\xa00.56\xa0mg GAE/g DM), flavonoids (from 2.65\xa0±\xa00.05 to 3.79\xa0±\xa00.11\xa0mg CAE/g DM), anthocyanins (from 0.75\xa0±\xa00.10 to 2.22\xa0±\xa00.10\xa0mg Cy-3G/g DM), antioxidant activity (from 33.03\xa0±\xa00.72 to 47.67\xa0±\xa00.39\xa0mg\xa0TE/g DM) and a more desirable overall appearance than fruits after hot air convective drying. Among different initial treatments, freezing provided the best results in terms of drying time. Sonication gave the best results for the retention of bioactive components, antioxidant activity and the overall appearance of dried fruits.