The Influences of Pectin and Apples, as a Pectin-rich Food Matrix, on Lipid Digestibility, Bioaccessibility and Postprandial Lipemia
Pectin, a common dietary fibre, can potentially modulate lipid digestion and postprandial lipemic response, which contributes to cardiovascular risks. This thesis used in vitro models to study how pectin, both in purified form and food matrices, can affect lipid digestion. A human trial was also undertaken to investigate the effects of consuming whole apples on postprandial lipemia. Firstly, the effects of pectin on the digestion of a soy lecithin-stabilized emulsion rich in docosahexaenoic acid (DHA) was studied using a static in vitro model. Different levels of pectin and gastric pH conditions were applied to represent realistic food composition and gastrointestinal dynamics in humans. Pectin led to changes in emulsion microstructure, which were reflected in lipid digestibility and DHA bioaccessibility results. Based on above findings, a randomized crossover trial was conducted with 26 overweight and obese adults to understand how consuming ~200 g whole apples, as a pectin-rich food matrix, can modulate postprandial lipemia induced by a high fat dairy beverage. Apple consumption did not change gastric emptying, postprandial lipemic or glycemic responses, but increased insulinemia, which was potentially induced by fructose and may have counteracted potential lipid lowering effects of apples. To study how whole apples affected emulsion stability, digestibility and bioaccessibility of the dairy beverages used in the human study, two in vitro digestion models (i.e. static with a gastric pH of 3.0 or 6.5 and dynamic (i.e. TIM-1) systems) were applied. Gastric pH was found to influence apples’ effects on emulsion stability and digestibility in the static model. In TIM-1, apples did not lower lipid bioaccessibility, in agreement with the no effect of apples observed in the human study. In summary, pectin and apples impacted in vitro emulsion stability and the subsequent lipid digestion and bioaccessibility, depending on factors including gastric pH, pectin content and meal fat content. In humans, apples did not alter postprandial lipemia. Overall, this thesis provides valuable insight about pectin and apples’ functionality regarding lipid metabolism, which applies to food and nutrition scientists and industries. It also highlights the need to improve the physiological relevance of in vitro digestion methods for lipid research.