Emulsion Droplet Physical State and Acid Stability Alter In Vitro Digestibility, and Postprandial Lipemia and Satiety in Healthy Men

The supramolecular structure of lipids in foods potentially modulates their digestibility, postprandial lipemia (PPL), and satiety, thereby contributing differently to health and disease risk. This thesis aimed to investigate the contributions of emulsion triacylglycerol (TAG) crystallinity to PPL and acute satiety using comprehensive physicochemical analyses, two human studies, and in vitro digestion experiments. The first human study showed that the presence of partially crystalline TAG droplets (SE) resulted in lower appetite suppressing effects in 15 healthy men, evidenced by subjective satiety ratings and satiety related hormones, compared to an emulsion of identical composition, but containing undercooled liquid lipid droplets (LE). In the second human study, emulsions containing liquid palm olein or palm stearin were prepared with emulsifiers resistant (Tween 80) or not (Span60) to gastric acid stability. In this case, a reduced duration of PPL was observed for the emulsions containing partially crystalline droplets (SS and SU), but PPL otherwise did not differ (P>0.05). The emulsion containing liquid state TAGs and which was resistant to acidic pH (LS) remained dispersed in the stomach and resulted in the highest level of short-term subjective satiety and corresponding satiety hormones (PYY and GLP-1) and lower hunger hormone ghrelin. Acid stability was a strong modulator of gastric emptying, as the two stable emulsions emptied more slowly based on gastric antrum ultrasound measurements, irrespective of the physical state of the emulsified lipids when an acid unstable emulsifier was present. Gastric ultrasonography measurements over time were shown to be superior to the acetaminophen marker method of gastric emptying, given the range of structures investigated. When SS, SU, LS, and LU were digested using the computer simulated dynamic in vitro system, TIM-1, the emulsion containing liquid lipid droplets that was acid stable had higher lipid bioaccessibility than the other emulsions which did not differ. Therefore, in the TIM-1, the presence of TAG crystallinity attenuated lipid digestion, irrespective of emulsion colloidal acid stability, although this trend was not seen in the human study. Collectively, this thesis provided valuable insights on the contributions of TAG physical state and the role of gastric structuring on digestibility, with implications for gastric emptying, lipemia, and satiety.