Effect of protein–surfactant interactions on aggregation of β-lactoglobulin

• Published in: Biochimica et biophysica acta Vol. 1814; no. 5; pp. 713 - 723
• Main Authors: Hansted, Jon G., Wejse, Peter L., Bertelsen, Hans, Otzen, Daniel E.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.05.2011
• Subjects: Calorimetry; Chromatography, Gel; Circular Dichroism; Emulsifier; Isothermal titration calorimetry; Lactoglobulins - chemistry; Protein Binding; Protein Stability; Sodium dodecyl sulfate; Sodium Dodecyl Sulfate - chemistry; Surface-Active Agents - chemistry; Surfactant; Thermal stabilization; Whey protein aggregate; βLG; SDS; DM; LTAC; xTAC; Whey protein aggregate; Thermal stabilization; Emulsifier; DDM; Surfactant; SxS; Sodium dodecyl sulfate; xM; RH; MES; Isothermal titration calorimetry
• ISSN: 1570-9639; 0006-3002; 1878-1454
• DOI: 10.1016/j.bbapap.2011.03.011

The milk protein β-lactoglobulin (βLG) dominates the properties of whey aggregates in food products. Here we use spectroscopic and calorimetric techniques to elucidate how anionic, cationic and non-ionic surfactants interact with bovine βLG and modulate its heat-induced aggregation. Alkyl trimethyl ammonium chlorides (xTAC) strongly promote aggregation, while sodium alkyl sulfates (SxS) and alkyl maltopyranosides (xM) reduce aggregation. Sodium dodecyl sulfate (SDS) binds to non-aggregated βLG in several steps, but reduction of aggregation was associated with the first binding step, which occurs far below the critical micelle concentration. In contrast, micellar concentrations of xMs are required to reduce aggregation. The ranking order for reduction of aggregation (normalized to their tendency to self-associate) was C10–C12>C8>C14 for SxS and C8>C10>C12>C14>C16 for xM. xTAC promote aggregation in the same ranking order as xM reduce it. We conclude that SxS reduce aggregation by stabilizing the protein's ligand-bound state (the melting temperature tm increases by up to 10°C) and altering its charge potential. xM monomers also stabilize the protein's ligand-bound state (increasing tm up to 6°C) but in the absence of charged head groups this is not sufficient by itself to prevent aggregation. Although micelles of both anionic and non-ionic surfactants destabilize βLG, they also solubilize unfolded protein monomers, leaving them unavailable for protein–protein association and thus inhibiting aggregation. Cationic surfactants promote aggregation by a combination of destabilization and charge neutralization. The food compatible surfactant sodium dodecanoate also inhibited aggregation well below the cmc, suggesting that surfactants may be a practical way to modulate whey protein properties. [Display omitted] ► Aggregation of the whey protein βLG is inhibited by sub-micellar anionic surfactants. ► This involves a combination of protein stabilization and increase of charge. ► Cationic surfactants promote aggregation below the cmc but inhibit it above the cmc. ► Non-ionic surfactants inhibit aggregation above the cmc despite destabilizing βLG. ► These different interactions can modulate the properties of whey aggregates.