Fluorescence Spectroscopy Investigation of Acid-or Rennet-Induced Coagulation of Milk

Herbert, S.; Riaublanc, Alain; Bouchet, Brigitte; Gallant, Daniel J.; Dufour, Éric

doi:10.3168/jds.s0022-0302(99)75446-9

Cited by 98 publications

(102 citation statements)

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“…The maximum in the emission spectra of TRP was found at a relatively higher value than in previous papers, 340-342 nm against 330-333 nm, either in emulsions with dairy proteins, in processed milk or in soft cheeses [9,10,17,18]. This shift of the maximum cannot be due to the heat treatment of milk.…”

Section: Front-face Fluorescence Spectroscopymentioning

confidence: 41%

“…This method might be regarded as a nondestructive, in situ, powerful and sensitive method, when associated with PCA, particularly recommended when studying a gelation under varying physicochemical environments such as acidification. During the acidification of unheated milk with GDL studied with intrinsic tryptophan (TRP), a shift of the maximum of spectra to lower wavelengths was evidenced, due to a more hydrophobic environment of TRP [17]. A first linear increase of the intensity at 320 nm versus pH was reported, followed by a second one with a higher slope.…”

Section: Introductionmentioning

confidence: 90%

“…Front-face fluorescence spectroscopy is a powerful technique for dynamic studies of colloidal non-transparent systems such as dairy emulsions [9], acid or rennet gels [9,[14][15][16][17] or even cheeses [11,18]. The fluorescence spectrum of a probe in the food product is related to its environment.…”

Section: Introductionmentioning

confidence: 99%

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Article

Laligant

Famelart

Pâquet

et al. 2003

Lait

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-The behaviour of heat-treated skim milk towards acidification by fermentation with lactic bacteria was studied at 30°C and 42°C. Rheological changes using dynamic oscillations and 1 H-NMR relaxation time, T2, were studied with time and pH. Front-face intrinsic fluorescence measurements studied with principal component analysis were performed during fermentation. The gel was formed at 42°C at a shorter time and a higher pH (5.53 ± 0.01) than at 30°C (5.24 ± 0.13). The maximum in tan d was higher at 42°C than at 30°C, but the G' values at pH 4.6 were the same at the two temperatures. The changes in T2 with pH were not greatly different at the two temperatures, but the dT2/dpH curves showed some differences with the temperature. The changes in T2 were due to the changes in the particle structure caused by the fermentation and were correlated with calcium solubilisation. Front-face fluorescence can detect a first shift of the maximal intensity toward lower wavelengths and a second shift toward longer wavelengths. These shifts were separated by the gel point and were due to changes in the environment of tryptophan residues in the protein chains. The discussion of these results and the comparison with GDL-induced gels take into account the limitation of the transfer of the acid and the protons from the aqueous to the colloidal phase and the subsequent heterogeneity of the gel.Milk / yoghurt / pH / 1 H-NMR / rheology / intrinsic fluorescence Résumé -Fermentation de lait reconstitué et chauffé par des bactéries lactiques à deux températures. II. Approche dynamique de la construction du gel. Le comportement du lait écrémé traité thermiquement au cours de l'acidification par des bactéries lactiques est étudié à 30 et 42°C. Les modifications rhéologiques par oscillations dynamiques et le temps de relaxation T2 en RMN du proton sont étudiés en fonction du temps et du pH. La fluorescence frontale intrinsèque étudiée conjointement avec l'analyse en composantes principales a été suivie au cours de la fermentation. La gélification du lait apparaît à un temps plus court et un pH plus élevé à 42°C (5,53 ± 0,01) qu'à 30°C (5,24 ± 0,13). Le pic de maximum de tan d était plus marqué à 42 qu'à 30°C, mais le G' à pH 4,6 avait la même valeur aux deux températures. Les changements de T2 au cours * Correspondence and reprints E-mail: famelart@rennes.inra.fr 308 A. Laligant et al.de l'acidification étaient peu différents aux deux températures étudiées, mais les courbes dT2/dpH montrent quelques différences entre 42 et 30°C. Les changements de T2 sont dus à des changements de structure de la particule provoqués par la fermentation et sont corrélés à la solubilisation du calcium. La fluorescence frontale détecte un premier décalage des spectres vers des longueurs d'onde plus petites puis un décalage vers des longueurs d'onde plus grandes. Le point associé à l'inversion de l'environnement des tryptophanes des chaînes protéiques correspond au point de gel. Ces résultats et les différences avec des gels acides obtenus par l'addition ...

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Section: Front-face Fluorescence Spectroscopymentioning

confidence: 41%

Section: Introductionmentioning

confidence: 90%

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Article

Laligant

Famelart

Pâquet

et al. 2003

Lait

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“…Considering the semi-hard cheeses such as Salers cheese, the interactions between the protein network and the fat globule vary, depending on the milk composition and on the manufacturing process (acidification rate), and modify in different ways the vitamin A spectra [7,14,15]. Crystallisation of the triglycerides during ripening time may also alter the shape of vitamin A fluorescence spectra [8,20].…”

Section: Correlations Between Sensory and Fluorescence Datamentioning

confidence: 99%

“…Principal Component Analysis (PCA) was applied to the physico-chemical data, to the stress/strain curves and to the normalised spectra in order to investigate changes in the data [14][15]. This statistical multivariate treatment makes it possible to draw similarity maps of the samples and to get spectral patterns [1,17].…”

Section: Multidimensional Analysis Of the Datamentioning

confidence: 99%

Delineation of the texture of Salers cheese by sensory analysis and physical methods

Lebecque

Laguet

Devaux

et al. 2001

Lait

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-The 25 investigated Salers cheeses graded by the professional committee offered a large range of textures. Their texture characteristics were investigated by sensory analysis, rheological measurements and fluorescence spectroscopy. The 8 sensory attributes generated by the panel included the evaluation of mechanical, geometric and surface properties, and allowed the characterisation of the texture of the investigated cheeses. The stress values at 20% compression ranged between 0.073 and 0.290 kPa. The fluorescence spectra of protein tryptophans and vitamin A were recorded directly on the samples. Principal component analysis and canonical correlation analysis were used to evaluate the data and to investigate the relationships between the different sets of data recorded on the same cheeses. All the methods used to analyse the cheeses allowed discrimination of the samples, i.e. the obtained data constituted fingerprints of the cheeses. Moreover, strong correlations were found between the sensory attribute domain and the instrumental domains. It was also suggested that the phenomena observed at molecular and macroscopic levels were related to the texture of the cheeses.cheese / texture / sensory analysis / rheology / fluorescence Résumé -Étude de la diversité de la texture du fromage de Salers par l'analyse sensorielle et les méthodes instrumentales. Les 25 fromages de Salers étudiés, gradés par le comité professionnel, présentaient une large gamme de texture. Leurs caractéristiques de texture ont été évaluées par analyse sensorielle, mesures rhéologiques et spectroscopie de fluorescence. Les 8 descripteurs sensoriels définis par le panel permettaient l'évaluation des propriétés mécaniques, géométriques et de surface; autorisant la description de la texture des fromages étudiés. Les valeurs de la contrainte à 20 % de compression s'échelonnaient entre 0,073 et 0,290 kPa. Les spectres de fluorescence des tryptophanes des protéines et de la vitamine A ont été enregistrés directement sur les échantillons. L'analyse en

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