Assessment of Vibration-assisted Freeze-drying Intensification on Selected Drying Parameters of Cranberries

Freeze-drying is one of the most effective methods for preserving high-value fruits, although its wider industrial application remains limited by long process times and high energy demand. This study evaluated the effect of low-frequency mechanical vibrations (100 Hz) on the freeze-drying of cranberries (Vaccinium macrocarpon) as a process intensification strategy. Conventional and vibration-assisted freeze-drying were compared in terms of moisture removal, water activity, drying kinetics, antioxidant activity, vitamin C content, and surface morphology. The application of mechanical vibrations accelerated moisture removal and reduced the total drying time from 22.5 h to 17.5 h, corresponding to a 22% reduction relative to the conventional process. The microbiologically safe threshold of aw < 0.20 was reached nearly 5 h earlier in the vibration-assisted variant. The initial moisture content of the cranberries was 87.17 ± 1.73%, whereas the final moisture content reached 7.17 ± 1.32% in the control samples and 6.58 ± 1.38% in the vibration-assisted samples. Antioxidant activity remained statistically unchanged after drying, with values of 0.56 ± 0.04, 0.54 ± 0.05, and 0.52 ± 0.04 for fresh, conventionally freeze-dried, and vibration-assisted freeze-dried cranberries, respectively (p = 0.512). Vitamin C content decreased after drying, from 121.38 ± 6.05 mg ascorbic acid/100 g in fresh fruit to 103.47 ± 5.15 and 98.26 ± 4.90 mg ascorbic acid/100 g in the conventionally freeze-dried and vibration-assisted samples, respectively (overall p = 0.0045), although no significant difference was observed between the two dried variants. Microscopic observations revealed the formation of surface microcracks and channels in the vibration-assisted samples, which likely facilitated vapour transport and enhanced sublimation efficiency. Overall, low-frequency mechanical vibration is an effective freeze-drying intensification strategy that significantly shortens process time while preserving the key nutritional and functional quality attributes of cranberries and therefore shows promise for the development of more energy-efficient drying systems.