Freeze-thaw cycle synergistic pulsed light pretreatment improves vacuum freeze drying of Chinese bayberry

Abstract

Conventional drying methods for fruits and vegetables often struggle to balance drying efficiency, product quality, and energy consumption. To overcome these limitations, this study innovatively developed three-step strategy for Chinese bayberry drying, integrating three freeze-thaw cycles (FTC) pretreatment, pulsed light (PL; 1000 mJ/cm², 6 cm, 15 flashes) pretreatment, and variable-temperature vacuum freeze-drying (VT-VFD; ramping from −20 °C to 25 °C). The results demonstrated that FTC (by enhancing porosity, connectivity, and permeability) combined with VT-VFD (by dynamic temperature rise), synergistically accelerated the drying process. Compared to constant-temperature VFD at −18 °C, 4 °C, and 25 °C, this combined approach reduced drying time by 11.32–72.19 % and energy consumption by 4.64–68.10 %. Additionally, it improved brittleness and reduced volume shrinkage, although it had a negative impact on color. Subsequent PL pretreatment effectively mitigated FTC induced color deterioration by inhibiting PPO and POD activities, reducing the ΔE value to 1.62, which closely approaches that of fresh samples. Moreover, compared to VT-VFD alone, the combined application of FTC and PL pretreatments yielded a “dual enhancement” in the retention of bioactive compounds and antioxidant capacity. Specifically, the retention rates of total phenolics, anthocyanins, and ascorbic acid increased by 37.97 %, 43.19 %, and 27.21 %, respectively, while DPPH and ABTS radical scavenging activities improved by 26.92 % and 49.16 %, respectively. Finally, PL pretreatment also enhanced microbial safety, reducing total bacterial by 0.93 log CFU/g and mold & yeast by 1.81 log CFU/g. By integrating physical field pretreatments with dynamic temperature-controlled drying, this study provides a broadly applicable model for the precision drying of other perishable fruits and vegetables.