Impacts of Time-to-Freeze on Quality Attributes of Low-Moisture Part-Skim Mozzarella Cheese

Abstract

This research investigated the effect of time-to-freeze (TTF) on key quality attributes of low-moisture part-skim (LMPS) Mozzarella cheese, including browning, free oil formation and meltability. Thin slabs (4-mm) of LMPS Mozzarella were frozen at four different rates: in a still air freezer (−22°C), in a non-isothermal blast freezer (−30°C), in a temperature-controlled bath (−30°C), and in an ethanol-dry ice bath (−70°C), with TTF ranging from 0.4 to 95 min. Numerical simulations of the transient heat conduction equation provided temperature profiles that were compared with the experimental data for all freezing methods. Frozen samples were stored at −22°C for 15–18 h, then thawed and analyzed for browning, free oil formation, and meltability using spectrophotometry and modified Schreiber tests. TTF variations did not significantly affect the quality attributes, but samples with a TTF of 95 min had higher levels of free surface water compared to unfrozen cheese. The formation of free surface oil increased significantly after TTF durations of 1.2, 19, and 95 min compared to unfrozen samples. Surface browning decreased after 95 min, likely due to the higher free water content. Rapid freezing methods, such as the ethanol-dry ice bath (−70°C), are effective for quick freezing, but the still air freezer yielded better quality cheese. Cheese frozen in a still air freezer exhibited less redness (a*) and more lightness (L*), indicating reduced surface browning. Additionally, it retained more free surface water, enhancing the structural integrity and overall quality of LMPS Mozzarella.