The influence of sucrose (0-40 wt %) on the thermal denaturation and functionality of whey protein isolate (WPI) solutions has been studied. The effect of sucrose on the heat denaturation of 0.2 wt % WPI solutions (pH 7.0) was measured using differential scanning calorimetry. Sucrose increased the temperature at which protein denaturation occurred, for example, by 6-8 degrees C for 40 wt % sucrose. The dynamic shear rheology of 10 wt % WPI solutions (pH 7.0, 100 mM NaCl) was monitored as they were heated from 30 to 90 degrees C and then cooled to 30 degrees C. Sucrose increased the gelation temperature and the final rigidity of the cooled gels. The degree of flocculation in 10 wt % oil-in-water emulsions stabilized by 1 wt % WPI (pH 7.0, 100 mM NaCl) was measured using a light scattering technique after they were heated at fixed temperatures from 30 to 90 degrees C for 15 min and then cooled to 30 degrees C. Sucrose increased the temperature at which maximum flocculation was observed and increased the extent of droplet flocculation. These results are interpreted in terms of the influence of sucrose on the thermal unfolding and aggregation of protein molecules.

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-A novel rapid and non-destructive front-face fluorescence method to quantify furosine and lactulose in heat-treated milk has been developed. The emission fluorescence spectra (305-450 nm) of tryptophans of proteins, and emission and excitation fluorescence spectra of fluorescent Maillard-reaction products were recorded directly on milk samples. Principal component analysis (PCA) and principal component regression (PCR) were applied to process the spectra obtained. The front-face fluorescence method can give valuable information on the quality of heattreated milk because it allows the evaluation of furosine and lactulose content simultaneously. The results were well correlated with those of the reference methods. The front-face fluorescence technique is relatively low-cost, rapid and non-destructive and it could replace existing conventional analytical techniques practiced for lactulose and furosine evaluation in dairy products.Milk / heat treatment / front-face fluorescence / tryptophan / Maillard-reaction products / furosine / lactulose Résumé -Détermination du lactulose et de la furosine dans le lait par spectroscopie de fluorescence frontale. Une méthode nouvelle et non destructive basée sur la spectroscopie de fluorescence frontale a été mise au point pour quantifier la furosine et le lactulose dans les laits chauffés. Les spectres d'émission (305-450 nm) de fluorescence des tryptophanes des protéines et d'excitation et d'émission de fluorescence des produits de la réaction de Maillard du lait ont été enregistrés. L'analyse en composantes principales (ACP) et la régression en composantes principales (RCP) ont été appliquées à la collection de spectres. Les résultats montrent que la spectroscopie de fluorescence frontale permet de caractériser sur les plans des propriétés physico-chimiques et de la qualité les laits chauffés : en effet la furosine et le lactulose peuvent être déterminés simultanément. Les résultats ont été comparés à ceux obtenus aux moyens des méthodes de référence et de fortes corrélations ont été Lait / traitement thermique / fluorescence frontale / tryptophane / composés de la réaction de Maillard / furosine / lactulose

Emission and excitation spectra of intrinsic fluorophores present in milk were used to evaluate changes in milk following thermal treatments in the 57-72 degrees C temperature range from 0.5 min up to 30 min. Alternatively, the concentrations of native alkaline phosphatase, lactoferrin, immunoglobulin G, bovine serum albumin, beta-lactoglobulin, and alpha-lactalbumin were determined in the same samples by enzymatic and immunochemical techniques. As principal component analysis applied to the normalized fluorescence spectra successfully discriminated different milk samples according to the temperature and time of thermal treatment, principal component regression was applied to predict the amounts of the native proteins investigated using fluorescence data. The results showed strong correlations between measured and predicted data for alkaline phosphatase and beta-lactoglobulin. This study has demonstrated that front-face fluorescence spectroscopy has a promising potential to become a rapid and nondestructive analytical technique for the evaluation of physicochemical changes in milk induced by low thermal treatment.

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