Heat-Induced Aggregation of Whey Proteins:  Comparison of Cheese WPC with Acid WPC and Relevance of Mineral Composition

Abstract

Heat-induced aggregation of whey proteins in solutions made from two commercial whey protein concentrates (WPCs), one derived from mineral acid whey (acid WPC) and the other from cheese whey (cheese WPC), was studied using polyacrylamide gel electrophoresis (PAGE), size exclusion chromatography (SEC), and transmission electron microscopy (TEM). Heat treatment (75 degrees C) of acid WPC solutions (12.0%, w/w, pH 6.9) resulted in formation of relatively small "soluble" aggregates that were predominantly disulfide-linked. By contrast, heat treatment of the cheese WPC solutions (under the same conditions) caused formation of relatively large aggregates, containing high proportions of aggregates linked by noncovalent associations. The rate of aggregation of both beta-lactoglobulin and alpha-lactalbumin at 75 degrees C, measured as the loss of native proteins by PAGE, was higher in the cheese WPC solution than in the acid WPC solution. Cross dialysis of the two WPC solutions resulted in alteration of the mineral composition of each WPC solution and reversing their heat-induced aggregation behavior. The results demonstrated that the mineral composition is very important in controlling the aggregation behavior of WPC products.

Influence of moderate electric fields on gelation of whey protein isolate

“…In general, both COV and MEF treatments have reduced considerably the contents of native whey proteins, and the denaturation levels observed were in good agreement with published literature (Anema & Li, 2003). In both heat-treated WPI solutions, the loss of BSA was faster than that of lg or lac, whereas the loss of lac was faster than that of lg thus agreeing with previous studies performed on whey protein (Havea et al, 2002). In particular, BSA was completely denaturated during the early stages of heating, since the corresponding band was lost after the first 5 min of heating at 85 o C. The decline in native lg was considerably slower than that of lac; after 15 min of heating at 85 o C, the protein bands associated with native lgA (~14%) and lgB (~6%) remained in the gel.…”

“…Faded bands appeared between native lg and lac bands, which were identified by several authors as non-native monomers (Manderson, Hardman, & Creamer, 1998;Schokker et al, 2000). Faint bands in the region between BSA and lg have become distinct after the first 5 min of heating, and are identified as intermediate protein groups, such as lg dimers and trimers, that were formed during heating (Cho, Singh, & Creamer, 2003;Havea et al, 2002). Heating at 85 o C resulted in a sharp decrease in "nativelike" lg and lac bands, and a concomitant appearance of both aggregate smears and high molecular mass protein aggregates bands (Fig.…”

“…With further heat treatment, free SH may rapidly interchange with existing disulfide bonds to generate new inter-and intramolecular disulfide bonds that will engage toward protein aggregation (Fairley, Monahan, German, & Krochta, 1996;Schokker, Singh, Pinder, & Creamer, 2000). The formation of intermolecular disulfide bonds by sulfhydryldisulfide interchange is considered one of the major mechanisms of protein aggregation, and is mainly governed by formation of lg oligomers that combine into large aggregates (Havea, Singh & Creamer, 2002).…”

“…However, the mechanism of protein unfolding and aggregation is complex and may be influenced by many factors, such as electrostatic and hydrophobic interactions, hydrogen bonding and di-sulfide cross-linking (Havea et al, 2002;Kazmierski & Corredig, 2003;Mulvihill, Rector, & Kinsella, 1990). Several studies have shown that the processes of protein unfolding and aggregation occur to different extents depending on the conditions prevailing in the aqueous solution (e.g.…”

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

“…These results suggest that in the presence of 10 mmol·L -1 CaCl 2 , heating induced the formation of large aggregates, which were removed by the filtration step. This is consistent with the results of Havea et al [12] who reported that, after heating, the size of formed aggregates was larger in cheese WPC (calcium-rich WPC) than in acid WPC.…”