Cheese-Matrix Characteristics During Heating and Cheese Melting Temperature Prediction by Synchronous Fluorescence and Mid-infrared Spectroscopies

The structure and rheology characteristics of Comt, (hard cheese) and Raclette (semihard cheese) cheeses as a function of temperature were investigated using dynamic testing rheology and mid-infrared and synchronous front-face fluorescence spectroscopies. The storage modulus (G'), the loss modulus (GaEuro(3)), and the complex viscosity (eta*) decreased while strain and phase angle (tan delta) increased as the temperature increased from 20 to 80 A degrees C. SF (250-500 nm with Delta lambda = 80) and MIR (3,000-2,800 (fat region), 1,700-1,500 (protein region), and 1,500-900 cm(-1) (fingerprint region)) spectra were recorded on cheese samples at 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, and 80 A degrees C. The results showed that each spectroscopic technique provided relevant information related to the cheese protein and fat structures during melting, allowing the investigation of structural changes. In addition, the melting temperatures of cheese matrices and fats of the two cheeses were determined from the dynamic rheology data, SF spectra, and MIR spectra. Similar temperatures were obtained whatever the technique, since values of about 60 and 31 A degrees C were obtained for matrix and fat melting temperatures of Comt, and Raclette cheeses, respectively. No significant difference was observed between the results obtained with the three methods (significance level of 5%).