Lipid digestibility and bioaccessibility of a high dairy fat meal is altered when consumed with whole apples: Investigations using static and dynamic in vitro digestion models

It remains unclear how consuming whole apples, as a food matrix containing pectin and polyphenols, influences lipid digestibility and bioaccessibility from dairy-based meals. Pectin and polyphenols modulate lipid digestion in vitro, but their functionality can be altered by gastric pH, which is buffered by co-consuming dairy products. In the present study, a dairy meal containing 3 wt% protein and 10 wt% fat was digested with and without apples using static (i.e., adapted from INFOGEST standardized static model) and dynamic (TIM-1) in vitro methods to investigate the structure, digestibility, and bioaccessibility of milk fat from emulsion droplets in the presence of consumed apples. Furthermore, in the static digestion, the initial gastric pH was adjusted to 3.0 (i.e., acidic digestion, as INFOGEST protocol suggested) or remained unadjusted (pH = 6.5, i.e., neutral digestion, buffered by the dairy meal) to explore the effects of gastric acidity. Emulsion droplet structure and lipid digestibility in the static digestion were primarily influenced by gastric pH [mean lipolysis rate = 99.32 % and 83.95 % (p < 0.05) for the digestions with neutral and acidic pH in the gastric phase, respectively], but not the presence of apple. However, co-consumption of apples reduced the lipid bioaccessibility measured by TIM-1 [mean bioaccessibility = 65.44 % and 98.92 % (p < 0.05) for the digestions with and without apples, respectively]. Discrepancies in the bioaccessibility of individual fatty acids between the static and TIM-1 models were observed, which may be attributed to variations in the experimental parameters, e.g., chyme transit and enzyme concentration. Overall, this study shows the potential to preferentially modify lipid digestibility and bioaccessibility in high-fat meals by co-consuming apples. It also cautions attention to the digestive conditions of in vitro simulation studies when making comparisons to in vivo conditions.