Heat‐induced denaturation and aggregation of β‐Lactoglobulin: kinetics of formation of hydrophobic and disulphide‐linked aggregates

Abstract

Solutions of a whey protein mixture were subjected to various time/temperature treatments, at pH 6.7. Kinetic and thermodynamic activation parameters for the rates of irreversible denaturation/aggregation of the principal whey protein component-␤-lactoglobulin (␤-lg) were followed by gel permeation. Fast Protein Liquid Chromatography (non-dissociating, non-reducing conditions) and by SDS-PAGE (dissociating, non-reducing conditions). The rate of loss of native ␤-lg owing to the formation of disulphide linked protein aggregates (k S D S -P A G E ) and the rate of formation of aggregates via both covalent and non-covalent bonds (k G P -F P L C ) showed similar biphasic Arrhenius plots. However, the break of the plot occurred at different points. The k G P -F P L C values were higher than values of k S D S -P A G E for all the temperatures examined. There was a similar trend for the thermodynamic activation parameters implying that not all of the ␤-lg aggregates through thiol-disulphide interactions. Hydrophobically driven associations occur within the aggregates.

Influence of Run Time and Aging on Fouling and Cleaning of Whey Protein Deposits on Heat Exchanger Surface

“…Upon heating the whey protein solution forms a gel due to the reaction between the proteins molecules in the matrix forming many small monomers. These protein monomers contain a number of cysteine residues (Sawyer et al, 1985;Brownlow et al, 1997) and upon heating the free -SH groups of cysteine residues get oxidized and form disulfide bonds (Verheul and Roef, 1998;Galani and Apenten, 1999). These bonds are involved in cross-linking the protein monomers to form the aggregates (Galani and Apenten, 1999).…”

“…These protein monomers contain a number of cysteine residues (Sawyer et al, 1985;Brownlow et al, 1997) and upon heating the free -SH groups of cysteine residues get oxidized and form disulfide bonds (Verheul and Roef, 1998;Galani and Apenten, 1999). These bonds are involved in cross-linking the protein monomers to form the aggregates (Galani and Apenten, 1999). However, increasing the heating time provides more reaction time between the protein matrixes, increasing the number of disulphide cross-links between the protein molecules.…”

Mineral modulation of thermal aggregation and gelation of whey proteins: from ?-lactoglobulin model system to whey protein isolate

“…The relative proportion of these two types of interactions seems to be highly temperature-dependent. For instance, Galani and Apenten [8] showed that below 75°C, the noncovalent interactions contributed little to the overall aggregation process. They found that the contribution of noncovalent interactions to the aggregation becomes important at temperatures higher than 90°C.…”

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

“…Upon heating, betalactoglobulin dissociates into monomers, leading to exposure of hydrophobic groups and the free sulfhydryl group [9,10] . This then gives rise to aggregation and/or polymerization [4,5,9,11,12] . Beta-lactoglobulin is sensitive to heating at 60-100°C.…”

“…Beta-lactoglobulin is sensitive to heating at 60-100°C. During heating, the protein undergoes an initial dissociation of dimers followed by conformational changes which increase the exposure of previously buried hydrophobic groups and the thiol group [4,9,12,13,14] . Alpha-Crystallin is the major protein component of the mammalian eye lens, making up 50% of its dry weight [15,16] .…”