Synergetic interfacial adsorption of protein and low-molecular-weight emulsifiers in aerated emulsions

Abstract

Whipped creams (aerated emulsions) are a complex emulsion-foam system whose oil-stabilizing potential and aeration capacity are determined by the surface activity of proteins and small surfactants. In this study, the interaction between three low-molecular-weight (LMW) emulsifiers [sodium stearoyl lactylate (SSL), phospholipid (PL), and sucrose ester (SE)] with caseinate was investigated to elucidate the mechanism of formation and stability of whipped creams. Competitive adsorption, interfacial tension, droplet aggregation, viscosity, and morphological variations of the emulsions were examined, and aeration capacity, hardness, and microstructure of whipped creams were measured. The combination of surfactants (0.05–1.0% w/w) with caseinate (0.6% w/w) produced concerted effects on the stability of emulsions. Water-soluble surfactant (SE) adsorbed more strongly than oil-soluble surfactants (SSL and PL) onto oil droplets. The lesser protein adsorption in the SE emulsion enabled a strong foaming activity in the subsequent aeration. Protrusions of triacylglycerol crystals and aggregation of oil droplets into an interactive colloidal matrix with considerable hardness and viscosity were prominently observed in SE creams. On the other hand, shear thinning followed by thickening was observed when PL was added to form the caseinate-based emulsion while no foaming was produced, and SSL, known to form α-gel at the interface, produced no stable foam. The improved emulsion stability yet the propensity to coalesce induced by cooperative actions of casein molecules and hydrophilic surfactant played a crucial role in producing aerated emulsions.