Drying characteristics optimization of blanched day lily buds using a heat pump dryer

Abstract

Blanching significantly enhances the improvedrying conditions of day lily buds, yet there is limited information on optimal drying kinetics using heat pump dryers. This research aimed to optimize the drying characteristics of day lily buds by examining the drying rate and rehydration ratio. The heat pump drying air temperatures were set at 40 °C, 50 °C, and 60 °C, while blanching was conducted for 2, 4, and 6 minutes at the same temperatures. The average drying air velocity was maintained at 2.2 m/s, and relative humidity was controlled. Using the L₉(3³) Taguchi experimental design, the study identified the best combinations of parameters that maximized drying rate and rehydration ratio. Results indicated that increasing the blanching time from 2 to 6 minutes increased the drying rate of day lily buds from 1.098 kg/kg/min to 1.744 kg/kg/min. Similarly, increasing blanching temperature from 40 °C to 60 °C raised the drying rate from 1.382 to 1.468 kg/kg.min. Conversely, raising the air temperature from 40 °C to 60 °C resulted in a decreased drying rate from 1.491 kg/kg.min to 1.403 kg/kg.min. Rehydration ratios improved correspondingly, rising from 1.344 to 2.349 with the higher blanching time of 6 minutes. Also, an increase in blanching temperature enhanced the rehydration ratio from 1.835 to 1.976. Blanching time had more influence on both drying rate and the rehydration ratio of day lily buds, followed by blanching temperature and drying temperature, respectively. Ultimately, the optimal conditions for drying day lilies, 6 minutes of blanching at 60 °C with drying air temperature of 40 °C, promote high-quality, nutritious, and safe dried day lilies, preserving vitamins and increasing shelf life. Drying air temperature of 40 °C also ensures energy efficiency through lower drying temperatures as compared to 50 °C and 60 °C. © 2025 The Author(s)