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Subject: search.filters.subject.Beta-lactoglobulin

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    β-Lactoglobulin nanofibrils: Effect of temperature on fibril formation kinetics, fibril morphology and the rheological properties of fibril dispersions
    (Elsevier Ltd, 2012-05) Loveday SM; Wang XL; Rao MA; Anema SG; Singh H
    Almost all published studies of heat-induced b-lactoglobulin self-assembly into amyloid-like fibrils at low pH and low ionic strength have involved heating at 80 C, and the effect of heating temperature on self-assembly has received little attention. Here we heated b-lactoglobulin at pH 2 and 75 C, 80 C, 90 C, 100 C, 110 C or 120 C and investigated the kinetics of self-assembly (using Thioflavin T fluorescence), the morphology of fibrils, and the rheological properties of fibril dispersions. Self-assembly occurred at all temperatures tested. Thioflavin T fluorescence increased sigmoidally at all temperatures, however it decreased sharply with >3.3 h heating at 110 C and with >5 h heating at 120 C. The sharp decreases were attributed partly to local gelation, but destruction of fibrils may have occurred at 120 C. Thioflavin T fluorescence results indicated that maximal rates of fibril formation increased with increasing temperature, especially above 100 C, but fibril yield (maximum Thioflavin T fluorescence) was not affected by temperature. At 100 C and 110 C, fibrils were slightly shorter than at 80 C, but otherwise they looked very similar. Fibrils made by heating at 120 C for 1 h were also similar, but heating at 120 C for 8 h gave predominantly short fibrils, apparently the products of larger fibrils fragmenting. Heating at 100 C gave consistently higher viscosity than at 80 C, and heating for >2 h at 120 C decreased viscosity, which may have been linked with fibril fragmentation seen in micrographs.
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    Characterization of heat-induced aggregates of beta-lactoglobulin, alpha-lactalbumin and bovine serum albumin in a whey protein concentrate environment
    (Cambridge University Press, 2001) Havea P; Singh H; Creamer LK
    Bovine b-lactoglobulin (b-lg), a-lactalbumin (a-la) and bovine serum albumin (BSA), dispersed in ultra®ltration 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 twodimensional (2D) polyacrylamide gel electrophoresis (PAGE). When 100 g b-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 b-lg and a-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 b-lg, a-la and BSA, and 1:1 disulphide-bonded adducts of a-la and b-lg, or BSA. These results are consistent with a mechanism in which the free thiols of heattreated b-lg or BSA catalyse the formation of a range of monomers, dimers and higher polymers of a-la. It is likely that when whey protein concentrate is heated under the present conditions, BSA forms disulphide-bonded strands ahead of b-lg and that a-la aggregation with b-lg and with itself is catalysed by the heat-induced unfolded BSA and b-lg.