Effects of Drying Methods on Drying Characteristics and Physicochemical Quality of Turnip Slices (Brassica rapa L.)

To identify the optimal drying methods for turnip slices, vacuum freeze-drying (VFD), air impingement drying (AID), infrared-assisted hot air drying (IR-HAD), and conventional hot air drying (HAD) were evaluated. The physicochemical properties of dried samples were comprehensively assessed under varied drying conditions. The results demonstrated that AID achieved the shortest drying time (240 min). At identical temperatures, AID samples exhibited significantly lower total color difference (ΔE) compared with IR-HAD and HAD, alongside superior retention of total phenols and enhanced antioxidant activity. VFD yielded the highest quality attributes, including optimal rehydration capacity, maximal phenol retention, and the strongest antioxidant activity (DPPH: 16.56 ± 0.26 μmol Trolox/g; FRAP: 13.99 ± 0.04 μmol Trolox/g). SEM analysis revealed that VFD produced a loose, porous microstructure, explaining its enhanced rehydration. Overall, both AID (efficiency) and VFD (quality) show promise for industrial turnip processing.