In vitro Digestion of Oil-containing Hydrogels Using Gastric Digestion Simulator: a Model Analysis for Oil Release Control inside Human Stomach

Emulsion hydrogel that incorporates oil droplets are commonly used as food models due to easy manipulation of their mechanical characteristics and compositions. A novel in vitro gastric model called the “human gastric digestion simulator (GDS)” equipped with peristalsis enables the simulation and direct observation of the disintegration of food particles induced by peristalsis. The objective of this study was investigating the gastric digestion behavior of emulsion hydrogels with variable mechanical characteristics using the GDS. Four types of emulsion hydrogels containing soybean oil droplets were prepared, namely agar (AG), agar and native-type gellan gum (AG-NGG), deacetylated gellan gum (DGG), and deacetylated gellan gum and native -type gellan gum (DGG-NGG). During peristalsis in a GDS digestion experiment, DGG and DGG-NGG emulsion hydrogel shrank without releasing oil droplets, whereas AG and AG-NGG emulsion hydrogel disintegrated, releasing oil droplets. The disintegration and oil release rates for the AG-NGG emulsion hydrogel were lower than those for the AG hydrogel, where a linear relationship was observed between these two rates. The fracture stress and strain differed between these two hydrogels. The results indicate that lipid release from gels in the human stomach can be controlled by adjusting the gelling agent without changing the lipid