Kinetics of Formation and Physicochemical Characterization of Thermally-Induced β-Lactoglobulin Aggregates

• Published in: Journal of food science Vol. 75; no. 5; pp. E261 - E268
• Main Authors: Zúñiga, R.N, Tolkach, A, Kulozik, U, Aguilera, J.M
• Format: Journal Article
• Language: English
• Published: Malden, USA Blackwell Publishing Inc 01.06.2010; Wiley
• Subjects: aggregate size; beta-lactoglobulin; Biological and medical sciences; Chemical Phenomena; Chemistry, Physical; Chromatography, High Pressure Liquid - methods; denaturation; denaturation kinetics; electrophoresis; Electrophoresis, Polyacrylamide Gel - methods; food analysis; food composition; Food industries; food processing quality; Fundamental and applied biological sciences. Psychology; heat treatment; Hot Temperature; Hydrogen-Ion Concentration; kinetics; lactoglobulins; Lactoglobulins - analysis; Lactoglobulins - chemistry; Microscopy, Electron, Transmission - methods; Milk and cheese industries. Ice creams; model food systems; Particle Size; physicochemical properties; protein aggregates; Protein Denaturation; rate constants; Surface Properties; Thermodynamics; transmission electron microscopy; β-lactoglobulin; Heat treatment; denaturation kinetics; Denaturation; Size; β-Lactoglobulin; aggregate size; rate constants; Characterization; Milk protein; Transmission electron microscopy; Electrophoresis; Kinetics; Whey protein; Aggregate; Rate constant
• ISSN: 0022-1147; 1750-3841
• DOI: 10.1111/j.1750-3841.2010.01617.x

The kinetics of heat denaturation and aggregation for β-lactoglobulin dispersions (5% w/v) were studied at 3 pHs (6, 6.4, and 6.8) and at a heating temperature of 80 °C. Protein aggregates were characterized for hydrodynamic diameter, microstructure, and molecular weight by means of dynamic light scattering, transmission electron microscopy, and polyacrylamide gel electrophoresis, respectively. Concentration of native β-lactoglobulin decreased with holding time and with a decrease in the pH. Apparent rate constants were calculated for β-lactoglobulin denaturation applying the general kinetic equation solved for a reaction order of 1.5. Values of the apparent reaction rate constant k = 7.5, 6.3 and 5.6 x 10⁻³ s⁻¹ were found for pH 6, 6.4, and 6.8, respectively. Decreasing the pH of the dispersions produced higher aggregate sizes. After a holding time of 900 s, average hydrodynamic diameters for β-lactoglobulin aggregates at pH 6, 6.4, and 6.8 were 96, 49, and 42 nm, respectively. These results were confirmed by transmission electron microscopy images, where a shift in the size and morphology of aggregates was found, from large and spherical at pH 6 to smaller and linear aggregates at pH 6.8. β-Lactoglobulin formed disulfide-linked intermediates (dimers, trimers, tetramers) and so on) which then formed high molecular weight aggregates. From the results obtained by DLS, TEM, and SDS-PAGE a mechanism for β-lactoglobulin aggregation was proposed. This study shows that heat treatment can be used to produce protein aggregates with different sizes and morphologies to be utilized as ingredients in foods.