Characterization of heat-induced aggregates of β-lactoglobulin, α-lactalbumin and bovine serum albumin in a whey protein concentrate environment

Abstract

Bovine β-lactoglobulin (β-lg), α-lactalbumin (α-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 °C. The consequent protein aggregation was studied by one-dimensional (1D) and two-dimensional (2D) polyacrylamide gel electrophoresis (PAGE). When 100 g β-lg/kg permeate solution was heated at 75 °C, cooled and examined, large aggregates were observed. These aggregates were partially dissociated in SDS solution to give monomers, disulphide-bonded dimers, trimers and larger aggregates. When mixtures of β-lg and α-la or BSA were heated, homopolymers of each protein as well as heteropolymers of these proteins were observed. These polymer species were also observed in a heated mixture of the three proteins. Two-dimensional PAGE of mixtures demonstrated that these polymers species contained disulphide-bonded dimers of β-lg, α-la and BSA, and 1:1 disulphide-bonded adducts of α-la and β-lg, or BSA. These results are consistent with a mechanism in which the free thiols of heat-treated β-lg or BSA catalyse the formation of a range of monomers, dimers and higher polymers of α-la. It is likely that when whey protein concentrate is heated under the present conditions, BSA forms disulphide-bonded strands ahead of β-lg and that α-la aggregation with β-lg and with itself is catalysed by the heat-induced unfolded BSA and β-lg.

The influence of bovine serum albumin on β-lactoglobulin denaturation, aggregation and gelation

“…Both proteins were present in all the larger aggregates, whereas some very small aggregates only contained -lg. However, this result clearly confirmed similar observations (Gezimati et al, 1996;Havea et al, 2001) that all of the BSA was involved in covalently linked aggregates with -lg.…”

“…It contains 17 disulphide bonds and one free sulphydryl group. Previous studies have shown that the intermolecular disulphide bonds can be formed during both heat treatment and acidinduced gelation of whey protein mixtures (Matsudomi, Rector & Kinsella, 1991;Alting, Hamer, de Kruif & Visschers, 2000;Havea, Singh & Creamer, 2000;Havea, Singh & Creamer, 2001). Alting et al (2000) investigated the cold gelation of whey protein isolate (WPI), where the whey proteins are initially heat-denatured and gelation was induced by slow acidification at room temperature.…”

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

“…This lower amount in the mixed systems can be attributed either to the lower concentration of b-Lg or more probably to the concomittant formation of covalent heterodimers, e.g. between b-Lg and a-La, as already shown by Havea et al [11]. Figure 1 also shows that, for a given protein mixture, the proportion of this covalent b-Lg dimer at tg was lower in samples with added salts than in those without added salt.…”

RP-HPLC analysis of furosine and acid-soluble β-lactoglobulin to assess the heat load of extended shelf life milk samples in Austria

“…It is obvious that band intensity of acid-soluble whey proteins decreased corresponding to an increased heat load of milk samples analysed (from raw milk to UHT milk). The main whey proteins involved are in order of decreasing heat stability: α-La > β-Lg > BSA > immunoglobulins [1,4,17]. Thus, depending on heat stability of whey proteins, individual whey protein fractions decrease as a consequence of heating processes and can be used as a reliable tool to study the heat load of commercial milk samples.…”