In vitro digestion models to assess lipolysis: The impact of the simulated conditions of gastric and intestinal pH, bile salts and digestive fluids.

In vitro digestion models are a valid methodology to study nutrient hydrolysis by simulating standard physiological gastrointestinal conditions. However, there are pathologies in which some conditions are affected, which should be considered in the design of an in vitro digestion study. Our work aims at elucidating the role of different gastrointestinal conditions on lipolysis. In the context of exocrine pancreatic insufficiency, gastric pH, intestinal pH, bile salts composition, bile salts concentration, fat concentration in the digestion medium and volumetric ratio digestion fluid/food were the selected study parameters. The pH-stat method was applied to assess lipolysis extent and kinetics. Descriptive results were summarised in digestibility curves and beta regression models were used to explain the effect (odds ratio, OR) of the studied conditions on lipolysis. Additionally, distribution of emulsion droplets was measured and optical microscopy images of fat globules were taken in a selection of experimental conditions. Results showed that intestinal pH was the variable with the highest effect on lipolysis (OR 22.86, p < 0.001), followed by fat concentration in the digestion medium (OR 6.76, p < 0.001) and bile salts concentration (OR 1.56, p < 0.001). Overall, lipolysis was significantly associated with particle size (OR - 6.98, p < 0.001). We conclude that the assessment of lipolysis by means of in vitro digestion models is sensitive to the simulated gastrointestinal conditions, which should be adapted to the real physiological conditions occurring in altered health conditions.