Time-dependent polymerization of beta-lactoglobulin through disulphide bonds at the oil-water interface in emulsions.
Time-dependent intermolecular sulphydryl-disulphide interchange involving beta-lactoglobulin adsorbed at the oil-water interface in n-tetradecane-in-water emulsions (10 wt% oil, 0.5 wt% protein, pH 7.0) has been investigated using sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). While only monomers are detected in the adsorbed protein immediately after emulsion formation with pure beta-lactoglobulin, on storing the emulsion the amount of polymerized beta-lactoglobulin and the sizes of the oligomers are found to increase with time. There is no polymerization of adsorbed protein in emulsions made with pure alpha-lactalbumin after 72 h, or in emulsions made with beta-lactoglobulin in the presence of a reagent (N-ethylmaleimide) for modifying sulphydryl groups. Analysis by two-dimensional SDS-PAGE of adsorbed protein from aged emulsions made with a mixture of alpha-lactalbumin + beta-lactoglobulin shows some linking by disulphide bonds between alpha-lactalbumin and beta-lactoglobulin at the interface. Taken together with earlier time-dependent surface viscosity measurements, the results indicate the important role of free sulphydryl groups in the development of the high surface viscoelasticity of adsorbed globular proteins at the oil-water interface.
Dickinson
E
E
Procter Department of Food Science, University of Leeds, UK.
Matsumura
Y
Y
D000327:Adsorption; D000473:Alkanes; D004220:Disulfides / Q000737:chemistry*; D004591:Electrophoresis, Polyacrylamide Gel; D004655:Emulsions; D005033:Ethylmaleimide; D007768:Lactalbumin / Q000737:chemistry; D007782:Lactoglobulins / Q000737:chemistry*; D046911:Macromolecular Substances; D009821:Oils; D013438:Sulfhydryl Compounds / Q000737:chemistry; D013499:Surface Properties; D013997:Time Factors; D014783:Viscosity; D014867:Water
D000473:Alkanes; D004220:Disulfides; D004655:Emulsions; D007782:Lactoglobulins; D046911:Macromolecular Substances; D009821:Oils; D013438:Sulfhydryl Compounds; C024713:n-tetradecane; D014867:Water; D007768:Lactalbumin; D005033:Ethylmaleimide