Impact of temperature fluctuations during frozen storage on mozzarella cheese: insights from linear and nonlinear rheology and structure-function relationships

The short functional shelf-life of pasta-filata cheeses and their increasing global demand have attracted studies on the suitability of its frozen storage. However, the effects of temperature fluctuations (TF) during frozen storage (at −18 °C) on the structural and functional properties of low-moisture, part-skim (LMPS) mozzarella cheese remain unexplored. This study investigated the influence of different TF conditions on the linear and non-linear rheological behaviour, texture, and microstructure of commercial LMPS mozzarella blocks. The side and middle portions of LMPS mozzarella blocks were examined as distinct regions, identified from heat transfer profiles recorded using thermocouples and a data logger during freezing. Linear viscoelastic parameters (G', G") distinguished TF effects only within a limited temperature range and through power-law fitting of frequency sweep data (9.9–99 rad/s). In contrast, intracycle non-linear rheological indicators revealed strain-resolved transitions in shear-thickening ( T > 0) or thinning ( T < 0) below γ <24%, and two broad intracycle strain-stiffening ( S ) regions (1 < γ <44%; γ >59.2%) that varied with TF intensity and sample location. The Lissajous-Bowditch plots and principal component analysis confirmed rheo-behavioural clustering between thermally distinct regions and TF treatments. Intense temperature abuse resulted in significantly reduced total stretch work and stretch gradient compared to refrigerated and frozen control samples. Also, microstructural inhomogeneities in the protein-fat matrix were observed from confocal laser microscopy of cheese subjected to either rapid or slow TF treatments. Overall, TF intensity and thermal heterogeneity between side and middle region of LMPS mozzarella blocks resulted in notable differences in some rheological, textural, and functional properties.