Water status and dynamics of high-moisture Mozzarella cheese as affected by frozen and refrigerated storage.

High-moisture Mozzarella is one of the most exported cheeses worldwide, but affected by short shelf-life. Freezing can help to reduce waste, but its effect on quality needs to be considered. In this study, the physico-chemical changes of Mozzarella occurring during frozen storage and subsequent refrigerated storage (after thawing) were evaluated. Frozen cheeses stored at -18 °C between 1 and 4 months showed microstructural damage and different physical, textural, sensory properties. With NMR relaxometry it was possible to observe freeze-related dehydration of caseins, by measuring the changes in water relaxation times within the matrix. These modifications were confirmed by microstructural observations that showed the formation of larger serum channels in samples subjected to freezing, compared with fresh cheeses. Sensory evaluation showed skin peeling off in frozen samples. By observing the changes at various length scales it was therefore possible to identify the critical points affecting HM Mozzarella cheese quality during frozen storage.