title: Pressure-induced unfolding and aggregation of the proteins in whey protein concentrate solutions.
abstract: Whey protein concentrate solutions (12% w/v, pH 6.65 +/- 0.05) were pressure treated at 800 MPa for 20-120 min and then examined using size exclusion chromatography (SEC), small deformation rheology, transmission electron microscopy, and various types of one-dimensional (1D) and two-dimensional (2D) polyacrylamide gel electrophoresis (PAGE). The pressure-treated samples showed a time-dependent loss of native whey proteins by SEC and 1D PAGE and a corresponding increase in non-native proteins and protein aggregates of different sizes. These aggregates altered the viscosity and opacity of the samples and were shown to be cross-linked by intermolecular disulfide bonds and by noncovalent interactions using 1D PAGE [alkaline (or native), sodium dodecyl sulfate (SDS), and SDS of reduced samples (SDS(R))] and 2D PAGE (native:SDS and SDS:SDS(R)). The sensitivity of the major whey proteins to pressure was in the order beta-lactoglobulin B (beta-LG B) > beta-LG A > bovine serum albumin (BSA) > alpha-lactalbumin (alpha-LA), and the large internal hydrophobic cavity of beta-LG may have been partially responsible for its sensitivity to high-pressure treatments. It seemed likely that, at 800 MPa, the formation of a beta-LG disulfide-bonded network preceded the formation of disulfide bonds between alpha-LA or BSA and beta-LG to form multiprotein aggregates, possibly because the disulfide bonds of alpha-LA and BSA are less exposed than those of beta-LG either during or after pressure treatment. It may be possible that intermolecular disulfide bond formation occurred at high pressure and that hydrophobic association became important after the high-pressure treatment.
authors.affiliation: Fonterra Research Centre, Private Bag 11 029, and Riddet Centre and Institute of Food, Nutrition and Human Health, Massey University, Private Bag 11 222, Palmerston North, New Zealand.
authors.forename: Hasmukh A
authors.initials: HA
authors.lastname: Patel
authors.forename: Harjinder
authors.initials: H
authors.lastname: Singh
authors.forename: Palatasa
authors.initials: P
authors.lastname: Havea
authors.forename: Thérèse
authors.initials: T
authors.lastname: Considine
authors.forename: Lawrence K
authors.initials: LK
authors.lastname: Creamer
mesh_terms: D002850:Chromatography, Gel; D003432:Cross-Linking Reagents; D004220:Disulfides / Q000737:chemistry; D004591:Electrophoresis, Polyacrylamide Gel; D006874:Hydrostatic Pressure; D008854:Microscopy, Electron; D008894:Milk Proteins / Q000737:chemistry*; D017510:Protein Folding; D012996:Solutions; D014783:Viscosity; D000067816:Whey Proteins
chemical_list: D003432:Cross-Linking Reagents; D004220:Disulfides; D008894:Milk Proteins; D012996:Solutions; D000067816:Whey Proteins