Coffee melanoidins as emulsion stabilizers

The use of conventional food stabilizers (e.g., surfactants and animal-derived proteins) is not in line with consumer demands for natural products. This has led to a great interest in novel emulsion stabilizers. In this paper, we explore the emulsification properties of coffee melanoidins, which are brown polymers made up by polysaccharides, proteins and polyphenols formed during bean roasting. The physical properties and stability of oil-in-water (O/W) emulsions (10 wt% oil) stabilized with 0.25–4 wt% coffee melanoidins were investigated upon storage. Coffee melanoidins can form emulsions with a nearly monomodal size distribution. Upon 28 days of storage at room temperature, emulsions prepared with low (0.25–1 wt%) melanoidin concentrations underwent creaming, flocculation, and coalescence; emulsions prepared with high (4 wt%) melanoidin concentrations gradually transformed from a liquid-like state to a gel-like structure, and emulsions prepared with 2 wt% melanoidins were physically stable. Stabilization of the emulsions is explained by both interfacial effects and an increased viscosity at high melanoidin concentrations. Surface load determination, confocal laser scanning microscopy (CLSM), and polarized light microscopy revealed that polysaccharide-rich melanoidins were able to adsorb at the droplet surface. We conclude that coffee melanoidins act both as emulsifiers (decreasing the interfacial tension and inducing electrostatic and steric repulsion) and texture modifiers (increasing the viscosity of emulsions). Coffee melanoidins can be used as natural emulsifiers in targeted food products.