Light-Scattering Study of the Structure of Aggregates and Gels Formed by Heat-Denatured Whey Protein Isolate and β-Lactoglobulin at Neutral pH

Université du Maine, Le Mans, Pays de la Loire, France
Journal of Agricultural and Food Chemistry (Impact Factor: 2.91). 04/2007; 55(8):3104-11. DOI: 10.1021/jf063029g
Source: PubMed


The structure of aggregates and gels formed by heat-denatured whey protein isolate (WPI) has been studied at pH 7 and different ionic strengths using light scattering and turbidimetry. The results were compared with those obtained for pure beta-lactoglobulin (beta-Lg). WPI aggregates were found to have the same self-similar structure as pure beta-Lg aggregates. WPI formed gels above a critical concentration that varied from close to 100 g/L in the absence of added salt to about 10 g/L at 0.2 M NaCl. At low ionic strength (<0.05 M NaCl) homogeneous transparent gels were formed, while at higher ionic strength the gels became turbid but had the same self-similar structure as reported earlier for pure beta-Lg. The length scale characterizing the heterogeneity of the gels increased exponentially with increasing NaCl concentration for both WPI and pure beta-Lg, but the increase was steeper for the former.

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    • "Dans le cadre des travaux menés au sein du laboratoire BIA de l'INRA de Nantes sur les propriétés moussantes de biopolymères, la βlg est couramment utilisée comme protéine modèle. Ses mécanismes d'agrégation étant parfaitement connus (Mahmoudi et al., 2007), des agrégats de taille et de forme diverses peuvent être obtenus en jouant sur les conditions du milieu. Ainsi, en changeant la concentration initiale en protéines (de 1 à 10 g/L), nous avons pu obtenir des agrégats de taille variable par traitement thermique pendant 24 h à 80°C (Figure 7). "
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    • "The pD was measured with a standard pH electrode and the value was corrected according to pD ¼ pH þ 0.4. The solutions of aggregated BLG were prepared according to the work of Mahmoudi et al. (2007). The principles are reported in Scheme 1. "
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    ABSTRACT: Native proteins usually undergo structural modification upon adsorption at interface. Heat treatments are commonly applied at the industrial scale and lead to aggregation of proteins. We characterized nanometric aggregates of β-lactoglobulin by infrared spectroscopy in solutions, in hexadecane oil-in-water emulsions and at the air–water interface at low and high (0.1 M) ionic strengths and at pH 7. In solutions, on the contrary to native β-lactoglobulin, all aggregates prepared with or without salt possessed intermolecular β-sheets evidenced by two strong absorption bands at 1614 cm−1 and 1682 cm−1. In emulsions, at low ionic strength, they lose their intermolecular β-sheets once they are adsorbed at the oil–water interface. At high ionic strength, most of aggregates are localized at the interfaces where they lose their intermolecular β-sheets in direct contact with the surface and only partially when they are farther from the interface. The loss of intermolecular β-sheets was similarly observed at the air–liquid interface.
    Full-text · Article · Dec 2013 · Food Hydrocolloids
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    • "Investigations on the heat-aggregation behaviour of β-LG or WPI model solutions clearly show that of all factors, the control of electrostatic repulsion between the reactant proteins affects the final size of the heat-induced complexes. As a rule, increasing the ionic strength of the medium decreases the range and intensity of electrostatic repulsion, thus increasing the chance for aggregation, and the size of complexes (Baussay et al. 2004; Caussin and Bouhallab 2004; Durand et al. 2002; Mahmoudi et al. 2007; Pouzot et al. 2005; Unterhaslberger et al. 2006; Xiong 1992). Also, having the pH close to the pI of the reactant whey proteins enhances aggregation and yield larger, clustered complexes (Foegeding et al. 2002; Mehalebi et al. 2008; Vasbinder and de Kruif 2003). "

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