Concentration-dependent structural retention in freeze-dried reconstructed grape matrices formulated with...

High-sugar fruit matrices are prone to shrinkage and pore collapse during freeze-drying because concentrated sugar-acid phases provide limited solid support. This study investigated the concentration-dependent structural retention of reconstructed Shine Muscat grape matrices prepared with 2%, 4%, 6%, 8%, and 10% (w/w) pregelatinized corn starch (PGS) dispersions, denoted PGS-D2, PGS-D4, PGS-D6, PGS-D8, and PGS-D10, respectively. Texture, force-relaxation, and rheological measurements were combined with Fourier transform infrared spectroscopy (FTIR), low-field nuclear magnetic resonance (LF-NMR), differential scanning calorimetry (DSC), micro-computed tomography (Micro-CT), and scanning electron microscopy (SEM) to characterize mechanical response, pre-freezing viscoelasticity, molecular environments, proton mobility, thermal behavior, and final pore architecture. Within the tested concentration range, the shrinkage ratio decreased progressively from PGS-D2 to PGS-D8 and did not differ significantly between PGS-D8 and PGS-D10 (p > 0.05). Compared with PGS-D2, PGS-D8 showed an approximately fivefold increase in compression hardness and a marked increase in storage modulus (G'), together with smaller layer-wise porosity fluctuations and more continuous pore walls. Increasing the PGS dispersion concentration to 10% did not further improve volume retention and was accompanied by greater spatial heterogeneity in the pore structure. The combined results revealed coordinated concentration-dependent changes in pre-freezing viscoelastic properties, hydroxyl-associated molecular environments, relative proton mobility, mechanical response, and final pore organization. Among the tested formulations, PGS-D8 exhibited a comparatively favorable balance among volume retention, compression resistance, and spatial pore uniformity. These findings establish links between pre-freezing network properties and final pore architecture and provide a multiscale basis for formulating structurally stable freeze-dried reconstructed fruit products.