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 (h*) decreased while strain and tan d 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.Cheese / structure / texture / melting / fluorescence / rheology Résumé -La spectroscopie de fluorescence frontale : un outil pour l'étude de la fonte des fromages -Corrélations avec les données rhéologiques. L'évolution de la texture et de la structure de deux fromages à pâte pressée cuite (Comté et Emmental) et un fromage à pâte pressée non cuite (Raclette) en fonction de la température a été déterminée par des mesures rhéologiques (test d'oscillation) et par spectroscopie de fluorescence frontale. Le module d'élasticité (G'), le module de perte (G'') et la viscosité complexe (h*) diminuent lorsqu'on fait varier la température entre 5 et 60 °C. Cependant, on note un accroissement de la déformation et de la tangente de l'angle de perte, tan d, dans la même gamme de température. Les spectres d'émission des tryptophanes de protéines et les spectres d'excitation de la vitamine A ont également été enregistrés sur des échantillons de fromages à 5, 10, 15, 20, 25, 30, 35, 40, 50 et

Utilisation of front-face fluorescence spectroscopy for the determination of some selected chemical parameters in soft cheeses

“…The shape of the spectra changes with the manufacturing process of the investigated cheeses. Recently, it has been reported that the shape of the vitamin A excitation spectrum is correlated with the physical state of the triglycerides in the fat globules [14,22,23]. Considering the short distance between tryptophan residues and vitamin A in the cheese matrix, fluorescence transfer between a donor (tryptophan) and an acceptor may be observed.…”

“…Indeed, much less information is available about the relation between the shape of the vitamin A spectra and the organisation of lipids than the shape of the tryptophan spectra and the protein structure. However, it is well known that the fluorescent properties of this fluorophore are very sensitive to changes in the solvent viscosity [19,22,23]. Recently, a good correlation between the shapes of the vitamin A fluorescence spectra and the viscosity of lipids in the fat globules have been found [14].…”

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

“…Small-amplitude oscillatory shear or compression measurements were successfully used to study the viscoelastic behavior of food (Bertola et al 1992;Bowland and Foegeding 2001;Campanella et al 1987;Rosenberg et al 1995) and cheeses (Karoui et al 2003).…”

Relations Between Spectral and Physicochemical Properties of Cheese, Milk, and Whey Examined Using Multidimensional Analysis

“…2b). The fluorescence intensity ratio F 320 /F 295 attributed to the physical state of the triglycerides of milk fat (Dufour et al 2000;Karoui et al 2003) increased from the young to ripened cheeses and shifted towards higher wavelengths with ripening. Hence, the excitation spectra of vitamin A characterize the physical state (viscosity) of the triglycerides in the milk fat and fat yield in the cheeses in the course of cheese ripening.…”