Light-Scattering Study of the Structure of Aggregates and Gels Formed by Heat-Denatured Whey Protein Isolate and β-Lactoglobulin at Neutral pH
ABSTRACT 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. "
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 · 4.28 Impact Factor
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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). "
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 · 4.28 Impact Factor
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ABSTRACT: The formation of complexes between whey proteins and κ-casein during heat treatment of milk dramatically affects the protein organisation in both the colloidal casein and the serum phases of milk and consequently, its technological applications. This paper reviews the composition and building interactions of these complexes and their localisation between the casein micelle and lactoserum. The currently proposed mechanisms that lead to their formation are also presented. The physico-chemical properties of these complexes, in terms of structure, size and surface properties are described and the technological means by which these properties could be controlled are discussed. Finally, the current hypotheses that explain the functional properties of these complexes in the heat-induced changes of dairy applications are reviewed, with emphasis on acid gelation of milk. /κ-/κ- La formation de complexes entre les protéines sériques et la caséine κ au cours du traitement thermique du lait modifie profondément l’organisation des protéines dans la phase caséine micellaire et dans le lactosérum, et par conséquent ses aptitudes technologiques. Cet article fait l’état de l’art de la composition, des interactions impliquées dans les complexes et de leur localisation entre caséine micellaire et lactosérum. Les mécanismes actuellement proposés pour décrire la formation de ces complexes sont présentés. Les propriétés physico-chimiques des complexes, telles que leur structure, leur taille et leurs propriétés de surface, sont décrites et les moyens technologiques permettant de moduler ces propriétés sont discutés. Enfin, les hypothèses actuellement proposées pour expliquer les propriétés fonctionnelles des complexes au cours des procédés de transformation du lait sont exposées, avec une attention particulière pour la gélification acide du lait. heat treatment–whey protein–κ-casein–complexDairy Science and Technology 01/2009; 89(1):3-29. DOI:10.1051/dst:2008033 · 1.13 Impact Factor