Characterization of heat-induced aggregates of beta-lactoglobulin, alpha-lactalbumin and bovine serum albumin in a whey protein concentrate environment.
Bovine beta-lactoglobulin (beta-lg), alpha-lactalbumin (alpha-la) and bovine serum albumin (BSA), dispersed in ultrafiltration permeate, that had been prepared from whey protein concentrate solution (100 g/kg, pH 6.8), were heated at 75 degrees C. The sequent protein aggregation was studied by one-dimensional (1D) and two-dimensional (2D) polyacrylamide gel electrophoresis (PAGE). When 100 g beta-lg/kg permeate solution was heated at 75 degrees C, cooled and examined, large aggregates were observed. These aggregates were partially dissociated in SDS solution to give monomers, disullphide-bonded dimers, trimers and larger aggregates. When mixtures of beta-lg and alpha-la or BSA were heated, homopolymers of each protein as well as heteropolymers of these proteins were observed. These polymer species were also served in a heated mixture of the three proteins. Two-dimensional PAGE of mixtures demonstrated that these polymers species contained disulphide-bonded dimers of beta-lg. alpha-la and BSA, and 1:1 disulphide-bonded adducts of alpha-la and beta-lg, or BSA. These results are consistent with a mechanism in which the free thiols of heat-treated beta-lg or BSA catalyse the formation of a range of monomers, dimers and higher polymers of alpha-la. It is likely that when whey protein concentrate is heated under the present eonditions. BSA forms disulphide-bonded strands ahead of beta-lg and that alpha-la aggregation with beta-lg and with itself is catalysed by the heat-induced unfolded BSA and beta-lg.
Havea
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Institute of Food, Nutrition and Human Health, Massey University, New Zealand.
Singh
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Creamer
L K
LK
D000818:Animals; D002417:Cattle; D004591:Electrophoresis, Polyacrylamide Gel / Q000662:veterinary; D005782:Gels; D006358:Hot Temperature / Q000009:adverse effects*; D007768:Lactalbumin / Q000737:chemistry*; D007782:Lactoglobulins / Q000737:chemistry*; D008894:Milk Proteins / Q000737:chemistry*; D011489:Protein Denaturation; D012710:Serum Albumin, Bovine / Q000737:chemistry*; D013997:Time Factors; D000067816:Whey Proteins
D005782:Gels; D007782:Lactoglobulins; D008894:Milk Proteins; D000067816:Whey Proteins; D012710:Serum Albumin, Bovine; D007768:Lactalbumin