Fluorescence spectroscopy: A tool for the investigation of cheese melting - Correlation with rheological characteristics

Abstract

Trends in the texture and structure as a function of temperature were determined for 2 hard cheeses (Comté and Emmental) and 1 semi-hard cheese (Raclette) using dynamic testing rheology and front-face fluorescence spectroscopy. The storage modulus (G′), the loss modulus (G″) and the complex viscosity (η*) decreased while strain and tan δ increased as the temperature increased from 5 °C to 60 °C. Protein tryptophan emission spectra and vitamin A excitation spectra were recorded on cheese samples at 5, 10, 15, 20, 25, 30, 35, 40, 50 and 60 °C. For each cheese, the data sets containing fluorescence spectra and rheology data were evaluated using principal component analysis and factorial discriminant analysis. It was shown that the maps defined by principal components 1 and 2 discriminated cheese samples as a function of temperature whatever the data (dynamic testing rheology data or fluorescence spectra). In addition, the melting temperature of fats for the three cheeses determined from the dynamic rheology data and the vitamin A fluorescence spectra gave similar results, i.e., 30, 32 and 31 °C for Emmental, Comté and Raclette cheeses, respectively. Canonical correlation analysis was applied to cheese dynamic rheological measurements and tryptophan and vitamin A fluorescence spectral collections in order to measure the link between the groups of variables measured on the same samples. The rheology and fluorescence groups of variables were found to be highly correlated since the squared canonical coefficients for canonical variables 1 and 2 were higher than 0.94 and 0.49, respectively.