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.
"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. "
[Show abstract][Hide abstract] 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.
"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). "
"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). "
[Show abstract][Hide abstract] 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.
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.