Release of Free Fatty Acids (FFA) during In VitroDigestion
The release of Free Fatty Acids (FFA) from both emulsions was closely monitored at various time points during intestinal digestion, and the results are depicted in Figure 7. The lipid digestion profiles of the emulsions produced by HPH and MF displayed similar patterns, characterized by an initial rapid increase in FFA levels followed by a more gradual rise over time until reaching a relatively stable final value.
Although there were no significant differences observed between the KO emulsions prepared by HPH and MF during the initial stages of digestion, some distinctions became apparent in the profiles of fatty acid release and the initial rates of lipid digestion. Notably, the MF-prepared emulsions exhibited a lower initial rate of lipid digestion. This difference can be attributed to alterations in the surface area of lipids exposed to digestive enzymes, a factor that is inversely proportional to the mean droplet diameter. As the digestion process advanced, the oil droplets within the homogenized emulsion tended to aggregate. This aggregation resulted in a reduction in the surface area of the oil droplets, limiting lipase’s access to the droplet surfaces. This phenomenon aligns with findings from another study (Qin et al., 2016), which reported that the rate and extent of lipid digestion in aβ -carotene emulsion increased with decreasing mean droplet diameter (small ≈ medium >> large). Moreover, it’s worth noting that the MF-prepared emulsion exhibited a higher final extent of FFA release compared to the HPH-prepared emulsion. The final release of FFA from the MF-prepared emulsion reached approximately 80.72±1.05%, whereas the HPH-prepared emulsion released only 67.41±1.6% of FFAs. Several factors may contribute to this difference, including the resistance of colloidal particles to digestion and the potential hydrolysis of lipids before analysis due to emulsion instability. It is noteworthy that the HPH-prepared emulsion exhibited numerous non-digested lipid droplets, as observed through confocal microscopy (Figure 5A). This observation aligns with the relatively low extent of lipid digestion by the end of the small intestine phase. These findings emphasize the role of smaller particle size in nanoemulsions in enhancing the bioavailability of encapsulated hydrophobic nutraceuticals by facilitating more rapid and complete digestion of the lipid phase.