Heat-Induced Whey Protein Gels: Protein−Protein Interactions and Functional Properties

Abstract

Heat-induced gelation (80 degrees C for 30 min or 85 degrees C for 60 min) of whey protein concentrate (WPC) solutions was studied using small deformation dynamic rheology, small and large deformation compression, and polyacrylamide gel electrophoresis (PAGE). The WPC solutions (15% w/w, pH 6.9) were prepared by dispersing WPC powder in water (control), 1% (w/w) sodium dodecyl sulfate (SDS) solution, and N-ethylmaleimide (NEM) solution at a protein/NEM molar ratio of 1:1 or in 10 mM dithiothreitol (DTT) solution. PAGE analyses showed that the heat treatment of control solutions contained both disulfide and non-covalent linkages between denatured protein molecules. Only disulfide linkages were formed in heated SDS-WPC solutions, whereas only non-covalent linkages were formed in DTT-WPC and NEM-WPC solutions during heating. In heated NEM-WPC solutions, the pre-existing disulfide linkages remained unaltered. Small deformation rheology measurements showed that the storage modulus (G') values, compared with those of the control WPC gels (approximately 14000 Pa), were 3 times less for the SDS-WPC gels (approximately 4000 Pa), double for the NEM-WPC gels (approximately 24000 Pa), and even higher for the DTT-WPC gels (approximately 30000 Pa). Compression tests suggested that the rubberiness (fracture strain) of the WPC gels increased as the degree of disulfide linkages within the gels increased, whereas the stiffness (modulus) of the gels increased as the degree of non-covalent associations among the denatured protein molecules increased.

Effect of superfine grinding on the structural and physicochemical properties of whey protein and applications for microparticulated proteins

“…In comparison, sWPC-80 exhibited a similar SDS-PAGE profile with individual subunits of α-lactalbumin, β-lactoglobulin, and BSA, which indicated that superfine grinding did not influence the protein distribution of WPC. Furthermore, addition of β-mercaptoethanol broke existing intramolecular disulfide linkages and prevented formation of new intermolecular disulfide bonds, restricting protein aggregation to only non-covalent linkages (24). SDS-PAGE results explained that superfine grinding could not induce non-covalent associations of WPC molecules, but could not indicate the formation of intermolecular disulfide bonds.…”

Protein denaturation and functional properties of Lenient Steam Injection heat treated whey protein concentrate

“…Denaturation of B-LG leads to disulfide interchange reactions and a redistribution of the -SH groups (Monahan, German, & Kinsella, 1995), hence it influences the ability to form heat induced gel networks. Also, non-covalent linkages are involved in the formation of the gel network, and it has been reported that an increased amount of noncovalent association leads to increased stiffness (modulus) of the formed gel, whereas an increased amount of disulfide linkages increases the fracture strain of the gel (Havea, Watkinson, & Kuhn-Sherlock, 2009). …”

Protein denaturation of whey protein isolates (WPIs) induced by high intensity ultrasound during heat gelation

“…Whey is used for e.g. texture enhancement in formulated products such as processed meat, bakery products and dairy products, and the utilization has progressed significantly due to extensive research and interest in understanding whey proteins as functional ingredients (Havea, Watkinson, & Kuhn-Sherlock, 2009;Kresic, Lelas, Jambrak, Herceg, & Brncic, 2008). …”