Dynamic Rheological Properties and Microstructure of Frozen Mozzarella Cheese

N. GRAIVER,; A. CALIFANO; N. ZARITZKY

SCANNING

Scanning Microscopy International. FAMS, Inc.

Lugar: Mahwah, NJ; Año: 2001 vol. 23 p. 215 - 216

0161-0457

The objective of this work was to analyze the effect of freezing low-moisture Mozzarella on cheese microstructure and its relationship with casein degradation and viscoelastic properties. Half of the samples were ripened at 10ºC for different aging times (0, 7, 16 and 23 days, controls) while the remaining samples were frozen at  –20ºC. After thawing they were stored at 10ºC to complete the desired ripening condition (F-R). Both soluble nitrogen (SN) and non-protein nitrogen (NNP, soluble in 12% trichloro acetic acid) contents were measured to analyze proteolysis by Hull’s method. Samples were dried in a vacuum oven at 80ºC to constant weight to determine moisture content. Micrographs from control and F-R samples were taken on an Environmental Scanning Electron Microscope (ESEM, Philips). Dynamic rheological analysis was performed to determine the elastic or storage modulus (G¢) and the viscous or loss modulus (G¢¢) that characterize the viscoelastic behavior of the system using an oscillatory rheometer (Haake CV20) with 30 mm parallel plates. The linear viscoelastic range was established between 20ºC and 60oC. Frequency sweeps were run at 50oC using a constant deformation of 5% (0.01-10Hz). G¢ at 1Hz and 4.63Hz were linearly correlated with the SN and NNP content of the samples showing that the elastic component decreased as proteolysis progressed. Ice crystals formed during the freezing process weakened the casein matrix, accelerating proteolysis. As the casein degradation products contribute less to the elastic modulus than the intact casein, cheese samples that had gone through a freezing-thawing cycle before ripening showed less elastic characteristics than the refrigerated controls.