Hybrid microwave-hot air drying of the osmotically treated carrots

Abstract

The influence of the hot air drying (HAD) and the hybrid drying (microwave drying followed by HAD) with (MWODHAD) or without (MWHAD) previous osmotic dehydration (OD) was evaluated on the effective moisture diffusivity (Deff), volumetric shrinkage (Sh), rehydration, carotenoid content and color of sliced carrots. The OD was performed with a ternary solution of sucrose and sodium chloride (35 °C; 300 min). The HAD procedure was carried out at 70 °C (1.5 m/s) and the MWHAD was tested using three different power levels (55.7, 167.9, 336.8 W) until the final moisture content of 0.13 ± 0.01 kg H2O/kg dry matter (DM). The results showed that the use of MWHAD with the highest power, reduced (p < 0.05) the total drying time (144 min) and increased the Deff compared to the HAD. Moreover, the MWHAD treatment showed the highest values of Sh, rehydration and carotenoid content. The sliced carrots dried using these three drying arrangements had no significant differences in color. In general, the combined treatment MWHAD could improve the drying rate and the quality.