Composite whey protein–cellulose nanocrystals at oil-water interface: Towards delaying lipid digestion

Lipid digestion is an interfacial process that is largely controlled by the adsorption of lipase + colipase + bile salts onto the surface of the emulsified lipid droplets. Therefore, engineering oil-in-water (O/W) interfaces that prevent competitive displacement by bile salts and/or delay the transportation of lipase to the hydrophobic lipid core can be effective strategies to delay lipolysis. In this study, we present such an interface using composite protein-particle system, consisting of whey protein isolate (WPI) (1 wt%) + cellulose nanocrystals (CNCs) (1–3 wt%). Droplet size, microscopy at various length scales (confocal, electron microscopy), ζ-potential and kinetics of fatty acid release were used to assess how the presence of CNCs impacted the microstructural stability of the emulsions in in vitro duodenal conditions (pH 6.8, 37 ○C). Adding CNCs at sufficiently high concentrations (3 wt%) significantly decreased the rate and degree of lipolysis as compared to that of protein-coated emulsion droplets. The principal cause of this altered lipolysis profile was the binding of bile salts by CNCs, which restricted both the interfacial displacement and solubilisation of lipid-digestion products by bile salts. The CNCs can be envisaged to be strongly bound to the protein-coated droplets by virtue of hydrogen bonding with the underlying protein. Furthermore, the ability of the CNCs in the continuous phase to bridge several protein-coated droplets reduced the overall surface area available for the lipolysis. Composite WPI + CNC interface holds promise in designing physiologically relevant emulsions to target satiety or delivery systems for sustained release of lipophilic components.