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

Abstract

Protein adsorption plays a key role in membrane fouling in liquid processing, but the specific underlying molecular mechanisms of β-lactoglobulin adsorption on ceramic silica surfaces in premix membrane emulsification have not been investigated yet. In this study, we aimed to elucidate the β-lactoglobulin adsorption and its effect on the premix membrane emulsification of β-lactoglobulin-stabilized oil-in-water emulsions. In particular, the conformation, molecular interactions, layer thickness, surface energy of the adsorbed β-lactoglobulin and resulting droplet size distribution are investigated in relation to the solvent properties (aggregation state of β-lactoglobulin) and the treatment of the silica surface (hydrophilization). The β-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 β-lactoglobulin. Although the conformation of the adsorbed β-lactoglobulin layer varies with membrane treatment and the solvent properties, the β-lactoglobulin adsorption offsets the effect of hydrophilization of the membrane so that the surface energies after β-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.

Keywords: Ceramic membranes; Conformation; Fouling; Molecular interactions; Protein adsorption.