Effects of Slice Thickness and Hot-air Temperature on Drying Characteristics, Physico-chemical Properties and Antioxidants of Mulusasiatica Nakai Slices

To study the effects of hot air temperature and slice thickness on the drying characteristics, physicochemical properties and antioxidant components of Mulusasiatica Nakai slices. The Mulusasiatica Nakai slices with thickness of 3 mm and 5 mm were dried in the hot air temperature range of 60, 70, 80, 90 ℃. Five classical food thin layer drying models were used to nonlinear fit the experimental data, and the diffusion coefficient and activation energy were calculated. The color, hardness, rehydration properties and antioxidant components of the dried slices were analyzed. Results showed that, the drying time was obviously shortened with the increase of hot-air temperature and the decrease of slice thickness. In the experimental drying temperature range, the effective diffusion coefficient increased with the increase of temperature. The activation energies were 17.46 kJ/mol and 23.82 kJ/mol when the slice thickness was 3 and 5 mm, respectively. Fick diffusion model was used to describe the evaporation process of Mulusasiatica Nakai slices. Compared with other models, Page model could better fit the drying process of Mulusasiatica Nakai slices. When the slice thickness was 3 mm and the hot-air temperature was 90 ℃, the dried product was light yellow, with high rehydration performance and low hardness. In terms of antioxidant retention, heat lost about 50% of ascorbic acid, but only about 35% of total phenolics. In conclusion, the slice thickness could be selected to be 3mm, the hot air temperature 90 ℃ for drying, drying time 90 min, dried product color was light yellow, higher rehydration performance, lower hardness, and could better retain the antioxidant components in Mulusasiatica Nakai.