Involvement of Disulfide Bonds in Bovine β‐Lactoglobulin B Gels Set Thermally at Various pH

Abstract

To obtain information on forces important for maintenance of the structure of heat-set ␤-lactoglobulin gels, gels set from pure ␤-lactoglobulin at pH 3.0, 5.0, and 7.0 were solubilized in dissociating buffers, and solubilized material was characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and size exclusion high performance liquid chromatography. The gel formed at pH 7.0 was largely soluble in urea (or SDS), and this gel seemed to be built from covalently linked soluble aggregates, associating into a gel network mainly by strong noncovalent interactions. The gel set at pH 5.0 was solubilized only in the presence of a reducing agent, indicating that this gel structure was supported mainly by covalent disulfide bonds. The gel set at pH 3.0 was almost completely solubilized in SDS or urea without a reducing agent, showing the importance of noncovalent interactions in maintaining the gel structure.

Influence of moderate electric fields on gelation of whey protein isolate

“…For the development of protein gel, was used the WPI solution at 10% (w/w) and final pH was adjusted to 3.0 with 1 M of HCl (Merck, Germany). Heating WPI with high protein concentration (8e11%) and under acidic condi-tions can yield a gel stabilized by non-covalent bonding (Aymard, Nicolai, Durand, & Clark, 1999;Otte, Zakora, & Qvist, 2000). Electrical conductivity of the prepared WPI solutions ranged approximately from ca.…”

“…At acidic pH (far from the protein isoelectric point, which is ~5.2) and low ionic strength, a gel network form that is composed of fine strands in the order of nanometer in size (Ikeda & Morris, 2002;Kavanagh, Clark, & Ross-Murphy, 2000), where intermolecular covalent disulfide bonding is unlikely to occur (Aymard et al, 1999;Otte et al, 2000). WPI fine-stranded and transparent gels were produced at pH 3 after heating at 85 o C for 30 min.…”

Capillary electrophoresis for the analysis of food proteins of animal origin

“…Otte et al [81] studied the electrophoretic behavior of bovine CMP from rennet whey, using an untreated capillary under acidic, neutral and alkaline conditions. In rennet whey, CMP could be separated from whey proteins at low pH (70 mM phosphate buffer, pH 2.5), and some glycosylated CMP forms could be distinguished.…”

The Effect of Molecular Chaperone, Alpha-Crystallin, on the Heat-Induced Aggregation of Beta-lactoglobulin

“…beta-lactoglobulin undergoes heatinduced structural changes, which involve the exposure of buried hydrophobic groups and thiol groups [34] . By contrast [32] provided evidence that polymerization of beta-lactoglobulin into a gel network does not occur via disulphide linkages. They explain that disulphide linkages occur initially during heating and the association of the soluble aggregates into a network occurs by non-covalent bonding which is a hydrophobic and/or hydrogen bond interaction.…”

“…It has also been demonstrated that the chaperone action of Alphacrystallin increased with increasing pH [30] . At lower pH values, the aggregation of beta-lactoglobulin occurs more by hydrophobic (nucleation-dependent) mechanisms since disulphide bond cleavage is highly pH dependent (i.e., it is reduced at lower pH values) [31,32] . Thus, it was proposed that even though alpha-crystallin's chaperone action is reduced at lower pH values, it should be able to prevent betalactoglobulin aggregation better at lower rather than at higher pH values.…”