Controlled digestion of lipids from oil-laden core-shell beads with tunable core and shell design

Lipid digestion products released and absorbed further down in the small intestine can induce feelings of satiety and reduce food intake. To achieve controlled lipolysis, uniformly sized core-shell beads were designed with different dimensions (i.e., oil core size and calcium-alginate hydrogel shell thickness) and compositions (i.e., wax addition in the oil core, chitosan and glutaraldehyde addition in the shell) through an in-air microfluidic technique. We investigated lipolysis from these beads under simulated oral, gastric, and intestinal conditions following the standardized INFOGEST in vitro digestion model. Lipolysis kinetics were monitored by image analysis of the core size and automatic titration of the lipolytic products – free fatty acids. The hydrogel shell swells and remains intact throughout gastrointestinal incubation, while the lipid core shrinks due to lipid digestion. The lipolysis rate (μmol‧s⁻¹) scales linearly with the total lipid surface area, leading to a constant rate per unit of surface area of 14 μmol fatty acids‧m⁻²‧s⁻¹. This unifies the results obtained for varied core sizes and oil doses. A delay in the onset of intestinal lipolysis was observed for core-shell beads of which the shell layer swells greatly under gastric and early-stage intestinal incubations. This swelling extends the pathway for intestinal lipase diffusion to the core surface, thus delaying the onset of lipid digestion, which can be as long as 60 min. Furthermore, we found that both core gelation (i.e., wax addition) and tightening the shell (i.e., additional cross-linking) greatly suppress the onset and rate of digestion. These insights can be used to predict and fine-tune the lipolysis behavior of core-shell beads, which paves the way for their rational application in functional (food) products, for example, to control food intake.