Evaluation of Microwave Vacuum Drying Combined with Hot-Air Drying and Compared with Freeze- and Hot-Air Drying by the Quality of the Dried Apple Product

In this study, combined microwave vacuum drying (MVD) with hot-air drying was evaluated, and then compared with hot-air drying and freeze drying, by the quality of the created product. The aim was to show that MVD is a strong quality competitor with the conventional hot-air drying and the widely used, but expensive freeze drying. For raw material, Jonathan apple was used. The combined microwave vacuum drying consists of two steps, the hot-air pre-drying, and then the microwave vacuum drying. The MVD was made with a unique batch drying system. Chemical, (total phenolic compounds, free radical-scavenging activity, aromatic content) physical (hardness) and consumer-related (organoleptic, and microbiological) properties were measured as quality parameters. The results show that quality of the product made by MVD combined with hot-air pre-drying is higher than hot-air dried ones. By most of the measured quality parameters, microwave vacuum drying also provided higher quality product than freeze drying.