Impact of alcohols on the formation and stability of protein-stabilized nanoemulsions

Nanoemulsions are increasingly being used for encapsulation, protection, and delivery of bioactive lipids, however, their formation from natural emulsifiers is still challenging. We investigated the impact of alcohol on the formation and stability of protein-stabilized oil-in-water nanoemulsions prepared by high-pressure homogenization. The influence of different alcohols (ethanol, 1-propanol, and 1-butanol) at various concentrations (0–25% w/w) on the formation and stability of emulsions stabilized by sodium caseinate, whey protein isolate, and fish gelatin was investigated. The mean particle diameter decreased with increasing alcohol concentrations from 0 to 10% w/w, but extensive droplet aggregation occurred at higher levels. This phenomenon was attributed to enhanced protein–protein interactions between the adsorbed emulsifier molecules in the presence of alcohol leading to droplet flocculation. The smallest droplets (d < 100 nm) were obtained when 10% w/w 1-butanol was added to sodium caseinate-stabilized nanoemulsions, but relatively small droplets (d < 150 nm) could also be obtained in the presence of a food-grade alcohol (ethanol). This study demonstrated that alcohol addition might be a useful tool for producing protein-stabilized nanoemulsions suitable for use as delivery systems of lipophilic bioactive agents.