Characterization of β-lactoglobulin adsorption on silica membrane pore surfaces and its impact on membrane emulsification processes

Protein adsorption plays a key role in membrane fouling in liquid processing, but the specific underlying molecular mechanisms of beta-lactoglobulin adsorption on ceramic silica surfaces in premix membrane emulsification have not been investigated yet. In this study, we aimed to elucidate the beta-lactoglobulin adsorption and its effect on the premix membrane emulsification of beta-lactoglobulin-stabilized oil-in-water emulsions. In particular, the conformation, molecular interactions, layer thickness, surface energy of the adsorbed beta-lactoglobulin and resulting droplet size distribution are investigated in relation to the solvent properties (aggregation state of beta-lactoglobulin) and the treatment of the silica surface (hydrophilization). The beta-lactoglobulin adsorption is driven by attractive electrostatic interactions between positively charged amino acid residues, i.e., lysin and negatively charged silanol groups, and is stabilized by hydrophobic interactions. The strong negative charges of the treated silica surfaces result in a high apparent layer thickness of beta-lactoglobulin. Although the conformation of the adsorbed beta-lactoglobulin layer varies with membrane treatment and the solvent properties, the beta-lactoglobulin adsorption offsets the effect of hydrophilization of the membrane so that the surface energies after beta-lactoglobulin adsorption are comparable. The resulting droplet size distribution of oil-in-water emulsions produced by premix membrane emulsification are similar for treated and untreated silica surfaces.