Colloidal aspects of digestion of Pickering emulsions: Experiments and theoretical models of lipid digestion kinetics

Lipid digestion is a bio-interfacial process that is largely governed by the binding of the lipase-colipase-biosurfactant (bile salts) complex onto the surface of emulsified lipid droplets. Therefore, engineering oil-water interfaces that prevent competitive displacement by bile salts and/or delay the transportation of lipase to the lipidoidal substrate can be an effective strategy to modulate lipolysis in human physiology. In this review, we present the mechanistic role of Pickering emulsions i.e. emulsions stabilised by micron-to-nano sized particles in modulating the important fundamental biological process of lipid digestion by virtue of their distinctive stability against coalescence and resilience to desorption by intestinal biosurfactants. We provide a systematic summary of recent experimental investigations and mathematical models that have blossomed in the last decade in this domain. A strategic examination of the behavior and mechanism of lipid digestion of droplets stabilised by particles in simulated biophysical environments (oral, gastric, intestinal regimes) was conducted. Various particle-laden interfaces were considered, where the particles were derived from synthetic or biological sources. This allowed us to categorize these particles into two classes based on their mechanistic role in modifying lipid digestion. These are ‘human enzyme-unresponsive particles’ (e.g. silica, cellulose, chitin, flavonoids) i.e. the ones that cannot to be digested by human enzymes, such as amylase, protease and ‘human enzyme-responsive particles’ (e.g. protein microgels, starch granules), which can be readily digested by humans. We focused on the role of particle shape (spherical, anisotropic) on modifying both interfacial and bulk phases during lipolysis. Also, the techniques currently used to alter the kinetics of lipid digestion using intelligent physical or chemical treatments to control interfacial particle spacing were critically reviewed. A comparison of how various mathematical models reported in literature predict free fatty acid release kinetics during lipid digestion highlighted the importance of the clear statement of the underlying assumptions. We provide details of the initial first order kinetic models to the more recent models, which account for the rate of adsorption of lipase at the droplet surface and include the crucial aspect of interfacial dynamics. We provide a unique decision tree on model selection, which is appropriate to minimize the