Ultra-Fast Infiltration Behavior of Vacuum Freeze-Dried Apples

Porous materials display ultra-fast liquid infiltration arising from the interplay of multi-scale structures, yet how these hierarchies regulate liquid dynamics and mechanics remain poorly understood. Here, vacuum freeze-dried (VFD) apples are employed as a bioinspired model to elucidate the structure-infiltration coupling that gives rise to their characteristic "dual-crispness" texture (a rapid transition from roasted crunchiness to juicy crispness during oral rehydration). In vitro saliva rehydration assays reveal that the ultra-fast infiltration behavior of VFD apples drives this rapid transformation. Unlike conventional hot air-dried apples, which undergo structural collapse and yield a monotonous texture, VFD apples feature a synergistic multi-scale structures-macroporous networks, microcellular cracks, and molecularly exposed hydrophilic groups-that collectively reduce flow resistance, accelerate intercellular infiltration, and enhance saliva capture. This hierarchical coordination rapidly restores cell turgor pressure before swallowing, giving rise to the distinctive "dual-crispness" sensation. By linking multi-scale structure to infiltration kinetics, this study establishes generalizable design principles for rapid-rehydration foods and hydration-responsive functional materials.