Freezing of Mozzarella cheese by immersion in NaCl solutions

RIBERO, GG; RUBIOLO, AC; ZORRILLA, SE

Viña del Mar (Chile)

Congreso; 10th International Congress on Engineering and Food; 2008

International Association of Engineering and Food

The freezing of Mozzarella cheese by immersion in NaCl solutions may be an innovative procedure for the dairy industry because it combines conveniently salting and freezing processes. In this work, the influence of this type of freezing method and of the frozen storage of samples on the proteolysis, rheological behavior and microstructure of Mozzarella cheese was studied. Cheese slabs (2x10x10 cm3) were immersed in 23% NaCl solutions (control samples: 4ºC, 90 min; frozen samples: -15ºC, 180 min). These conditions ensured similar final average NaCl concentration in cheeses. Half of the frozen samples were immediately thawed at 4ºC. The other half was stored at -20ºC for 2 months and then thawed at 4ºC (frozen-stored samples). The samples were stored at 4ºC and assayed at 1, 7, 14, 20, 27, 34, and 41 days. Proteolysis was assessed by urea-PAGE, and RP-HPLC of water-soluble fraction at pH 4.6. Rheological tests were carried out in oscillatory mode. Strain sweeps were run (0.001£g0£0.1) at 20, 40, and 60ºC, and temperature sweeps were run from 20 to 65ºC (1.33ºC min-1, g0=0.005). Scanning electron microscopy was used to examine the cheese microstructure. Primary hydrolysis of caseins resulted from the action of the residual coagulant, the first-order kinetics constant for as1-casein degradation being 0.0179 day-1. No significant effect of the treatments studied was observed on the degradation of the main caseins. Small differences were observed from the RP-HPLC results, the detection of peaks with small chromatographic area after 20 days in frozen-stored samples being the main difference. The influence of temperature on complex viscosity was studied by an Arrhenius-type equation. Activation energy values of 15.9±0.4, 14.1±0.5 and 13.8±0.6 Kcal mol-1 were obtained at 41 days for control, frozen and frozen-stored samples, respectively. Similarly, small differences in cheese structure were observed in frozen and frozen-stored samples compared to control samples at 41 days, less defined honeycomb-like structure in frozen-stored samples being the main difference. Although the immersion freezing of Mozzarella cheese affects some of the studied parameters, the differences observed between frozen and frozen-stored samples with control samples were small. Therefore, it was considered that the immersion freezing could be useful for the manufacture and preservation of Mozzarella cheese.