Studies of mineral and moisture dynamics in freeze-thawed LMPS mozzarella using calorimetry and proton (1H) and solid-state 31P NMR

This study investigated changes in moisture and phosphorus environments of LMPS mozzarella subjected to freezing and thawing and temperature fluctuations (TF) during frozen storage using complementary thermal and nuclear magnetic resonance (NMR) techniques. Gaussian deconvolution of the endothermic region of differential scanning calorimetry (DSC) thermograms showed that freezable moisture was thermally heterogeneous, comprising two distinguishable fractions differing in T-onset, T-peak, spectral linewidth, and degree of physical confinement within the cheese matrix. Frozen storage (FrS; 3 months at −18°C), with or without intense slow-TF treatment (overnight warming from −18°C to 6°C followed by refreezing to −18°C, once per month), resulted in an approximately 11-13% relative decline in protein-bound unfreezable moisture compared with refrigerated controls (6°C), indicating redistribution towards a relatively free state. Complementary 1 H NMR measurements showed enhanced water mobility, with ∼2-fold increase in the long-T 2 component and a 14-17% increase in water self-diffusion coefficient (D) in FrS and slow-TF samples. Solid-state 31 P NMR further indicated that the major phosphorus populations remained broadly conserved, while downfield shifts and reduced linewidths of mobile and immobile 31 P resonances suggested changes in their local chemical environments. Collectively, the complementary thermal and NMR observations support a mechanistic framework in which longer frozen storage and slow-TF promotes redistribution of moisture towards more mobile states and alter phosphorus environments in LMPS mozzarella. These changes are consistent with a possible partial dehydration of the paracasein matrix and associated reorganisation of its mineral environment, although specific mineral phases and mechanistic pathways remain presumptive.