Abstract:
To improve the drying efficiency and quality of apple slices, we applied vacuum pulsation drying technology to the apple slice drying processes and explored changes in indicators such as drying characteristics, rehydration ratio, color, vitamin C (VC) content, and total flavonoid content under different drying temperatures (55, 60, 65, and 70 ℃), normal pressure holding times (2, 4, 6, 8, and 10 min), and vacuum holding times (5, 10, 15, 20, and 25 min). The apple slice drying time decreased with an increase in the drying temperature, increased with an increase in the normal pressure time, and first decreased and then increased with increasing vacuum holding time. The effective moisture diffusion coefficient was 1.69×10-11–3.63×10-11 m2/s. During the drying process, the internal temperature of the apple slices fluctuated in a stepwise manner, increasing rapidly during the normal pressure stage and then decreasing owing to heat absorption from water evaporation during the vacuum stage. The drying temperature, vacuum holding time, and normal pressure holding time had significant effects (P<0.05) on the rehydration ratio, color, total flavonoid content, and VC content. The rehydration ratio and VC content exhibited gradually decreasing trends with increasing drying temperatures. The comprehensive score was the highest (0.73±0.01) at a drying temperature of 60 ℃, normal pressure holding time of 2 min, and vacuum holding time of 10 min. Under these process conditions, the drying time, total flavonoid content, rehydration ratio, VC content, and ΔΕ were 288 min, 9.21±0.48 mg/g, 2.23±0.07, 1.36±0.02 mg/g, and 24.65±1.94, respectively. This study provides a theoretical basis for optimizing the process parameters of the drying of apple slices via vacuum pulsation and aids in improving their production quality and efficiency.