Impact of Protein Gel Porosity on the Digestion of Lipid Emulsions

The present study sought to understand how the microstructure of protein gels impacts lipolysis of gelled emulsions. The selected system consisted of an oil-in-water (o/w) emulsion embedded within gelatin gels. The gelatin-gelled emulsions consisted of a discontinuous network of aggregated emulsion droplets (mesoscale), dispersed within a continuous network of gelatin (microscale). The visco elastic properties of the gelled emulsions were dominated by the rheological behavior of the gelatin, suggesting a gelatin continuous microstructure rather than a bicontinuous gel. A direct relationship between the speed of fat digestion and gel average mesh size was found, indicating that the digestion of fat within gelatin-gelled emulsions is controlled by the ability of the gel's microstructure to slow lipase diffusion to the interface of fat droplets. Digestion of fat was facilitated by gradual breakdown of the gelatin network, which mainly occurred via surface erosion catalyzed by proteases. Overall, this work has demonstrated that the lipolysis kinetics of gelled emulsions is driven by the microstructure of protein gels; this knowledge is key for the future development of microstructures to control fat digestion and/or the delivery of nutrients to different parts of the gastrointestinal tract.