The impact of dietary fibers on lipid digestion within the gastrointestinal tract depends on their molecular and physicochemical properties. In this study, the influence of the electrical characteristics of dietary fibers on their ability to interfere with the digestion of protein-coated lipid droplets was investigated using an in vitro small intestine model. Three dietary fibers were examined: cationic chitosan; anionic alginate; neutral locust bean gum (LBG). The particle size, ζ-potential, microstructure, and apparent viscosity of β-lactoglobulin stabilized oil-in-water emulsions containing different types and levels of dietary fiber were measured before and after lipid digestion. The rate and extent of lipid digestion depended on polysaccharide type and concentration. At relatively low dietary fiber levels (0.1 to 0.2 wt%), the initial lipid digestion rate was only reduced by chitosan, but the final extent of lipid digestion was unaffected by all 3 dietary fibers. At relatively high dietary fiber levels (0.4 wt%), alginate and chitosan significantly inhibited lipid hydrolysis, whereas LBG did not. The impact of chitosan on lipid digestion was attributed to its ability to promote fat droplet aggregation through bridging flocculation, thereby retarding access of the lipase to the droplet surfaces. The influence of alginate was mainly ascribed to its ability to sequester calcium ions and promote depletion flocculation.
Solid lipid nanoparticles (SLNs) are being investigated for their ability to encapsulate and protect lipophilic bioactive compounds in foods, supplements, and pharmaceuticals. In this study, the phase inversion temperature (PIT) method was used to fabricate SLNs using a model surfactant (Brij 30, C 12 E 4) / oil (octadecane) / water system. Surfactant/oil/water (SOW) mixtures were maintained at a temperature above the PIT, and then rapidly cooled to a temperature below the lipid nanoparticle crystallization point. The PIT ( 40°C) was determined by monitoring the turbidity versus temperature profile of the SOW system during heating. The lipid nanoparticle crystallization point, melting point, and physical state were determined using differential scanning calorimetry (DSC). The stability of the lipid nanoparticles after fabrication depended on the storage temperature relative to the PIT and melting/crystallization points. At temperatures appreciably below their melting point (26°C), the lipid nanoparticles were completely solid and stable to aggregation. At temperatures around their melting point, the lipid nanoparticles were partially crystalline, which led to partial coalescence and gelation. At temperatures appreciably above their melting point but below their PIT, the lipid nanoparticles were completely liquid and prone to coalescence and phase separation. These results have important implications for optimizing the fabrication and storage conditions required to produce stable nanoemulsions suitable for utilization in commercial products using low-energy methods.
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