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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    • "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.
    Food Hydrocolloids 12/2013; 33(2):178–185. DOI:10.1016/j.foodhyd.2013.03.011 · 4.09 Impact Factor
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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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    • "Centrifugation of WPI solutions did not show either a top layer or a precipitate and were filtered through 0.2 mm pore size filters. The protein concentration was measured by absorbance at 280 nm using extinction coefficient 0.93 L/g/cm for k-casein, 0.81 L/g/cm for sodium caseinate (Oliva, Llabres, & Farina, 2001; Schmidt, Koops, & Westerbeek,1977) and 1.046 L/g/cm for WPI (Mahmoudi et al., 2007). "
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    ABSTRACT: Aggregates were formed by heating mixtures of whey protein isolate (WPI) and pure κ-casein or sodium caseinate at pH 7 and 0.1 M NaCl. The aggregates were characterized by static and dynamic light scattering and size exclusion chromatography. After extensive heat-treatment at 80 °C for 24 h, almost all whey proteins and κ-casein formed mixed aggregates, but a large proportion of the sodium caseinate did not aggregate. At a given WPI concentration the size of the aggregates decreased with increasing κ-casein or sodium caseinate concentration, but the overall self-similar structure of the aggregates was the same. The presence of κ-casein or caseinate therefore inhibited growth of the heat-induced whey protein aggregates. The results were discussed relative to the reported chaperone-like activity of casein molecules towards heat aggregation of globular proteins.
    Food Hydrocolloids 06/2009; 23(4-23):1103-1110. DOI:10.1016/j.foodhyd.2008.07.001 · 4.09 Impact Factor
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