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Kinetics of Formation and Physicochemical Characterization of Thermally‐Induced β‐Lactoglobulin Aggregates
Author(s) -
Zúñiga R.N.,
Tolkach A.,
Kulozik U.,
Aguilera J.M.
Publication year - 2010
Publication title -
journal of food science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.772
H-Index - 150
eISSN - 1750-3841
pISSN - 0022-1147
DOI - 10.1111/j.1750-3841.2010.01617.x
Subject(s) - chemistry , kinetics , transmission electron microscopy , dynamic light scattering , beta lactoglobulin , protein aggregation , denaturation (fissile materials) , reaction rate constant , crystallography , analytical chemistry (journal) , whey protein , chromatography , chemical engineering , nuclear chemistry , biochemistry , physics , quantum mechanics , nanoparticle , engineering
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 × 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.