Study On Dielectric Properties、Dynamic Rheological Properties And Microstructures Of Cheddar Cheese Changes During Ripening

The relationships between the dynamic rheological properties, dielectric properties and microstructure and maturity index of cheddar cheese during ripening 0-180 days were studied. By means of test results, The Deborah number was calculated, and the relationship between dielectric parameters and dynamic rheological parameters and maturity index was established. The extent of proteolysis and lipolysis were verified by microstructures of scanning electron microscope. The results as follows:1. The water content was decreased from the initial 35.05% to 33.04% from Od to 180d, the reduction was not obvious. The pH value was falling firstly and then rising, The lowest value 5.43 was at 45days,after 45days, pH value increased slowly.2. During ripening from Od to 180d, the pH4.6-WSN and 12% TCA-SN had a upward trend on the whole. The rising was fast in the 0-45days, gently in the 45-90 days, and not obvious in the 90 days later. This indicated that the cheese ripening entered in a stable stage after 90 days of maturation.3. Storage modulus and loss modulus of Cheddar cheese showed an upward changed trend with the extension of ripening time in a specific test frequency. The storage modulus and loss modulus of Cheddar cheese with different ripening time increased with test frequency. The storage modulus increases for the sample of long ripening time was obviously, and that of the sample of short ripening time was not evident.The trend of loss modulus was similar with storage modulus.4. Deborah number value was rising firstly and then falling with ripening time in a particular frequency, which showed the elasticity of cheese was rising firstly and then falling with the extension of ripening time.5. The dielectric constant ε’,dielectric loss factor ε’’and specific conductance a of Cheddar cheese were all decreased with maturity in the specific test frequency. The tangent value of loss angel tanδ was falling firstly and then rising.6. With oscillatory frequency of 0.5rad/s and 100rad/s, there were linear correlation between the storage modulus and loss modulus and maturity index pH4.6-SN/TN in different maturity, the correlation coefficient R2 was above 0.8, which indicated that the changes of storage modulus and loss modulus had a storage link with maturity index pH4.6-SN/TN. Under the frequencies of alternating electric field 0.3GHz,0.95GHz and 2.45GHz,there were linear relationships between dielectric constant e’,dielectric loss factor ε’’and specific conductance σ and maturity index pH4.6-SN/TN. At 2.45GHz, dielectric constant ε’and dielectric loss factor ε’with maturity index pH4.6-SN/TN coefficient R2 was 0.8395 and 0.9313, at 0.95GHz specific conductance σ and maturity index pH4.6-SN/TN coefficient R2 was 0.8813, that a good linear correlation between the two.7. In the 0th day, SEM scanning microstructure map the overall structure of Cheddar cheese was rough. In the 60th day, fat globules become smaller, protein micelles were smooth and glossy with a larger hole between micelles, protein hydrolysis and fat degradation of the morphology were obvious. In the 120th day, the accumulation structure like of protein disappeared, the protein micelles was like streamline, the holes become larger, and the fat globules gathered into kidney shape. In the 180th day, fat ball almost all disappeared and the marking of fat globules significantly increased after the disappearance, protein micelles become into fragmentation, black holes appeared continuously which the fatty degradation of cheese is outstanding.