Polysaccharide-based structured lipid carriers for the delivery of curcumin: An in vitro digestion study

The present work aimed at studying the in vitro digestion fate of κ-carrageenan (KC) or agar (AG) emulsion gels (EG), and KC oil-filled aerogels (OAG) in terms of their structural changes, lipolysis kinetics and curcumin bioaccessibility. On the one hand, both EG and aerogels showed large (70-200 µm) and heterogeneous particles after gastric conditions, indicating the release of bulk oil and gelled material. Nonetheless, this material release in the stomach phase was lower in the case of EG-AG and OAG-KC compared to EG-KC. After small intestinal conditions, EG and oil-filled aerogels presented a wide range of particle sizes probably due to the presence of undigested lipid material, gelled structures, as well as lipid digestion products. For the most part, adding curcumin to the structures' lipid phase did not cause of the structural modifications that occurred at the different in vitro digestion phases. On the other hand, the lipolysis kinetics was different depending on the type of structure. Amongst emulsion-gels, those formulated with κ-carrageenan presented a slower and lower lipolysis kinetics compared to those formulated with agar, which could be attributed to their higher initial hardness. Overall, the addition of curcumin in the lipid phase decreased the lipolysis in all the structures, which evidenced its interference in the lipid digestion process. The curcumin bioaccessibility reached high values (≈ 100 %) for all the studied structures, presenting a high solubility in intestinal fluids. This work unravels the implications of microstructural changes of emulsion-gels and oil-filled aerogels during digestion and their impact on their digestibility and subsequent functionality.