Bioinspired Oleic Acid–Triolein Emulsions for Functional Material Design

Abstract

Being amphiphilic lipids, these digestion products can selfassemble into a variety of lamellar and non-lamellar lyotropic liquid crystalline structures attractive for drug and nutrient delivery applications. [9] The dynamic composition of the lipolysis products during triglyceride digestion has a profound influence on the physicochemical properties of the colloidal structures. For example, surface-active lipolysis products can alter the interface of the emulsion particles and transfer water into the triglycerideoil phase. [10] They can further regulate the digestion process by competing with the lipase for the oil-water interface. [11] Their adsorption to the oil-water interface modifies the interfacial tension which, together with shear forces in the digestive tract, can further reduce the emulsion droplet size. The resulting increase in surface area for lipases to access their substrate can ultimately increase the digestion kinetics. Therefore, understanding the structure and properties of these biologically important systems contributes to the development of smarter food materials, which are of great interest for the food industry. [12] In addition to compositional changes, food colloids are also exposed to varying pH and ionic strength conditions as they travel along the digestive tract. While pH in the stomach can be very acidic, intestinal pH can reach alkaline pH values, with this broad pH range being one of the challenges of oral delivery of nutrients and drugs. [13,14] Such changes in the local microenvironment influence the ionization state of the carboxyl group of fatty acids. This modifies their solubility in aqueous media or in the hydrophobic interiors of the emulsion droplet, changing its interfacial properties and their potential to self-assemble into nanostructures. [15][16][17][18][19] The ionization state of acids at a given pH, however, is not exclusively dependent on their molecular structure. While the pK a of an isolated carboxyl group of monomeric fatty acid in water is 4.75, [20] different values are reported in literature for the apparent pK a of acids in self-assembled systems, strongly affected by a variety of parameters such as intermolecular interactions, presence of neighboring charges, dielectric constant, and ionic strength. [16,19,21,22] Therefore, these external parameters can indirectly affect the physicochemical properties of dispersions containing molecules that can be deprotonated. For the case of oleic acid (OA) in particular, reported values of apparent pK a at different conditions and environments range from 6.1 to 9.4. [16,19,23,24] Stimuli-responsive nanostructured emulsions can be utilized to innovate tailor-made materials in fields including biotechnology and food materials. This study reports the composition and pH-responsive colloidal and interfacial properties of the naturally abundant oleic acid-triolein-water emulsions, and applies the knowledge to the sustainable design of nanoemulsions. Small angle X-ray scattering, spinning drop tensiometry, multi-angle dynami...

Structure Formation in Tailor‐Made Buriti Oil Emulsion During Simulated Digestion

“…The broad correlation peak centered around 2.70 nm −1 can result from the form factor scattering of whey proteins and the scattering from the local arrangements of TAGs in the internal phase of the droplet. This was also reported in previous SAXS studies on triolein emulsions [26] and whey proteins. [44] The SAXS curve (Figure S6, Supporting Information) of the oral phase (pH 7.0) is similar to the curve of the original formulation (pH ≈ 6.5), with additional peaks at q = 1.36 nm −1 and q = 2.72 nm −1 .…”

“…Deprotonated oleic acid can significantly reduce the oil/water interfacial tension, allowing emulsification by simple stirring without needing high‐energy methods. [ 26 ] The switch of the remaining whey protein from positively to negatively charged once pH changes from 3.0 to 7.0 could also contribute to the FFAs to stabilize the emulsion.…”

“…Further, the pH-dependent protonation and deprotonation of the carboxyl group of FFAs modify their surfactant properties and are responsible for their pH-responsive self-assembly. [25][26] The high content of oleic acid and other unsaturated fatty acids in buriti oil and its high amount of hydrophobic nutrients such as carotenoids and vitamin E make this oil a promising stimuliresponsive material for studying nutrient bioaccessibility. The simulated intestinal digestions were carried out at different pH values (6.5, 7.0, and 7.5) to address the hypothesis that buriti emulsion's digestion structures are modified with pH from fatty acid protonation/deprotonation.…”