Text

theses

Different from conventional emulsions, Pickering emulsions are stabilized by interfacially-adsorbed solid particles. Pickering emulsions have gained great interest in the past decades due to their high stability against coalescence, Ostwald ripening, and the possibility to avoid the deleterious effects linked to emulsifiers used in conventional emulsions. To fulfill the strong market trend of formulating products that are not only edible in theory, but also maintain the consumer perception of being natural, “clean label” and “green”, this study was dedicated to developing particles from biomass-based resources to form Pickering emulsions with potential application in food, cosmetic and pharmaceutic products. As a simple, organic solvent-free process, media-milling was applied to modify two major biomass materials, native starch and cellulose. Three maize starches (normal maize starch, high-amylose maize starch and waxy maize starch) with different amylose/amylopectin ratios were physically modified through media milling process to form milled starch particles. The physiochemical properties of these starches during milling process, including particle size, crystallinity and gelatinization properties were studied. Emulsions stabilized by milled starch particles with different amylose/amylopectin ratios exhibited significant difference in terms of stabilization capability and rheological properties. Milled high-amylose maize starch particles have the best stabilization ability, followed by milled normal maize starch particles. Furthermore, the stabilization capacity of the milled starch particles improves with the increase of milling time. To investigate the feasibility of Pickering emulsions stabilized by milled starch as a novel food-grade formulation for encapsulation and delivery of lipophilic bioactive compounds, curcumin was selected as model delivery target and encapsulated in the oil phase of Pickering emulsion. The digestion profile of curcumin-loaded Pickering emulsion was studied using three in vitro digestion models, simulated static small intestinal digestion model, pH-stat lipolysis model and TNO’s gastrointestinal model (TIM-1). Simulated static small intestinal digestion model and pH-stat model indicated that the bioaccessibility of curcumin encapsulated in Pickering emulsion was enhanced compared with free curcumin suspended in bulk oil phase. A significant improvement of curcumin bioaccessbility was also observed in an emulsion system vs in bulk oil when using TIM-1 model, which simulates the entire human GI tract. Overall, the study's findings showed that curcumin encapsulated in Pickering emulsion stabilized by milled starch possesses benign stability against harsh gastric conditions as well as improved dissolution profiles in small intestinal tract. All are suggested that Pickering emulsion stabilized by milled starch exhibit high potential as encapsulate and delivery system for lipophilic bioactive compounds. Milled cellulose particles of sizes ranging from 38 nm to 671 nm with rod-like shapes have also been successfully fabricated using media milling. Media milling process led to a notable decrease in the particle size and crystallinity of milled cellulose particles with the increase of milling time. The milled cellulose particles were irreversibly adsorbed at the oil/water interface and formed stable emulsions with droplet size around 60~42 µm, which exhibited benign stability over a month storage. Milled cellulose stabilized emulsions also exhibited good stability against a wide range of pH (3, 5, 7, 9) and salt conditions (0.1~100 mM) with slight change in the droplet size. The rheological tests indicated the formation of gel network in the emulsions, which promoted the stability of the emulsions. The in vitro digestion profile and phase behavior of Pickering emulsions stabilized by milled cellulose were evaluated to investigate their feasibility for encapsulation and delivery of lipophilic bioactive compounds. Curcumin encapsulated in Pickering emulsions exhibited benign stability with less than 50% degraded after storage of 30 days. The digestion behavior of emulsions under simulated small intestinal conditions was characterized using a pH-stat lipolysis model. The digestion profiles of emulsions were markedly dependent on the type of lipid and digestion buffer employed in lipid digestion experiments. The rate and extent of lipolysis of emulsions with medium chain triglycerides (MCT) was greater than emulsions with long chain triglycerides (soy bean and canola oil), reaching complete hydrolysis during lipolysis process independent of bile salt and phospholipids concentration. The structure changes of emulsions during digestion were analyzed using optical and fluorescent imaging. Although the initial digestion rate of curcumin encapsulated in Pickering emulsions with soy bean and canola oil was slower than the corresponding conventional emulsions stabilized by Tween/Span, their total extent of lipolysis was higher than that of conventional emulsions under both fasted and fed intestinal digestion conditions. The bioaccessibility of curcumin encapsulated in Pickering emulsions was higher than in corresponding surfactant stabilized conventional emulsions. High-amylose maize starch with different fatty acids (C12:0, C14:0, C16:0, C18:0, C18:1) were complexed using two heat-moisture methods. The structure properties of different starch-fatty acid complexes, including size and shapes of nanoscale supramolecular structures formed, through heat and moisture treatment, were studied. Optical microscope and SEM analysis showed that starch-fatty acid complexes retained the Maltese cross and granular morphology of native starch. X-ray diffraction revealed the crystalline morphology of starch-fatty acid complexes with B- and V-type crystallinity. And the crystallinity of the complexes varied depending on the fatty acids and methods used. USAXS/SAXS experiments demonstrated that fatty acid chain length and level of saturation affected both the lamellar structure as well as the B-type crystalline of the complexes. Moreover, the processing methods also exhibited major influence on the nanostructure of complexes. The resistance of these starch complexes against enzymatic hydrolysis was increased based on the in vitro digestion measurements. And the hydrophobicity of these complexes was enhanced. This was manifested by increased contact angles. The capacity of these starch-fatty acid complexes to form Pickering emulsions was characterized. Starch-saturated fatty acid complexes were able to form stable emulsions that endured heat treatment of 60, 80 and 100℃. However, starch-unsaturated fatty acid complexes could not form stable emulsions. The barrier properties of these emulsions could be adjusted by heat treatment, which led to swelling of starches. Lipolysis profile of PMFs loaded emulsions suggested that certain heat treatment could reduce the accessibility of lipase towards oil droplets and release of PMFs during lipolysis by enhancing the coverage of granules onto the oil-water interface. In conclusion, particles derived from biomass resources starch and cellulose have been successfully fabricated to form Pickering emulsions using simple, environmental-friendly procedures. The resulting formulations were edible, ‘green’, have exhibited exceptional stability and a practical potential to encapsulate and control release of lipophilic ingredients, making them suitable for various applications in cosmetic, food and pharmaceutical industry.

ETD_8337

Ph.D.

Includes bibliographical references

by Xuanxuan Lu

doi:10.7282/T3XP7827

ETD doctoral

The author owns the copyright to this work.