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Author ORCID Identifier

https://orcid.org/0000-0003-3296-5133

AccessType

Open Access Dissertation

Document Type

dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Food Science

Year Degree Awarded

2021

Month Degree Awarded

May

First Advisor

David Julian McClements

Subject Categories

Food Chemistry | Food Processing | Other Food Science

Abstract

Curcumin is a yellow-orange crystalline substance found in certain foods (turmeric) that is claimed to exhibit a broad range of biological activities. Its application as a nutraceutical in functional foods and beverages is often limited by its relatively low solubility in aqueous media, its chemical instability, and its low bioavailability. Recent research suggests that colloidal delivery systems can overcome these hurdles and improve the efficacy and commercial value of curcumin in the food, supplement, and pharmaceutical fields. The purpose of this research was to develop colloidal delivery systems to improve the application of curcumin as a nutraceutical in foods. First, the chemical degradation of curcumin in oil-in-water emulsions and filled hydrogel beads (alginate and chitosan beads) was initially compared to that of curcumin in aqueous solutions (dimethyl sulfoxide, DMSO). The same amount of curcumin was encapsulated in all the delivery systems, and the emulsion and aqueous solution form of curcumin exhibited higher color intensity than the hydrogel beads. After being incubated in the samples under both acidic and neutral conditions for 15-days at 55 ºC in the dark, it was found that curcumin was more stable under acidic than neutral conditions. Interestingly, the encapsulation of curcumin in alginate beads actually promoted its degradation at both acidic and neutral pH, but encapsulation in chitosan beads enhanced its stability at pH 7 but reduced it at pH 3. The curcumin degradation rate increased in the following order: at pH 7, chitosan beads < emulsion < alginate beads < aqueous solution; at pH 3, emulsion < aqueous solutions < chitosan beads < alginate beads. Second, an innovative pH-driven method was used to load curcumin into emulsions and its efficacy was compared to other loading methods: oil-solubilization and heat-driven methods. The aim of using the pH-driven method was to improve the encapsulation efficiency. The oil-solubilization method involved dissolving powdered curcumin in the oil phase (60 oC, 2 h) and then forming a nanoemulsion. The heat-driven method involved forming a nanoemulsion and then adding powdered curcumin and incubating at an elevated temperature (100 oC, 15 min). The pH-driven method involved dissolving curcumin in an alkaline solution (pH 12.5) and then adding this solution to an acidified nanoemulsion (pH 6.0). Initially, the encapsulation efficiency of the curcumin in the three nanoemulsions was determined: pH-driven (93%) > heat-driven (76%) > conventional method (56%). The bioaccessibility of the colloidal delivery systems created using the pH-driven method was then compared to that in three commercial supplements that use different encapsulation technologies: Nature Made, Full Spectrum, and CurcuWin. The curcumin concentration in the mixed micelles decreased in the following order: CurcuWin ≈ pH-driven nanoemulsions > heat-driven nanoemulsions > conventional nanoemulsions >> Full spectrum > Nature Made. This result indicated our natural emulsion-based system was suitable for encapsulating and increasing the bioaccessibility of curcumin. Third, we compared the efficacy of three different colloidal delivery systems produced using the pH-driven method: curcumin nanocrystals; curcumin-loaded nanoemulsions; and curcumin-loaded soy oil bodies. A control was also used that consisted of curcumin powder dispersed in water. The nanoemulsions and oil bodies formed yellowish creamy dispersions that were stable to creaming, whereas the nanocrystals formed a cloudy yellow-orange suspension that was prone to sedimentation. The potential fate of the different delivery systems after ingestion was assessed using a gastrointestinal tract (GIT) model that consisted of mouth, stomach, and small intestine phases. The nanoemulsions and oil bodies were rapidly and fully digested, while the nanocrystals were not. All three systems were relatively stable to chemical transformation in the in vitro digestion model, but the nanocrystals gave a low bioaccessibility, whereas the other two systems had a high bioaccessibility, which was attributed to their ability to form mixed micelles that solubilized the curcumin. Fourth, we examined the physical and chemical stability of curcumin-loaded soybean oil bodies prepared using the pH-driven method. First, the impact of pH (from 6.5 to 8) on the stability of curcumin-loaded soymilk during storage was investigated at 4 ºC for 36 days. At this low storage temperature, more than 85% of the alkaline-sensitive curcumin was retained at all three pH values, without any evidence of color fading. The impact of holding temperature (4, 20, 37, and 55 ºC) on the physicochemical stability of the curcumin-loaded soymilks was then measured during storage at pH 7 for 14 days. At 4 and 20 ºC, the emulsions remained physically stable, most of the curcumin (> 90%) was retained, and there was no evidence of color fading. At the higher temperatures, however, the rate of curcumin degradation increased. For instance, around 30% and 70% of curcumin was lost when the soymilks were stored at 37 and 55 ºC, respectively. On the other hand, the soymilks remained physically stable throughout this period. Finally, we showed that curcumin can be successfully loaded into dairy milk using this approach, without adversely affecting milk fat globule stability. The physical and chemical stability of curcumin-loaded milk stored under different pH and temperature conditions was assessed. The impact of pH on the stability of the curcumin-loaded milk was investigated by storing the samples at 4 ºC for 60 days at pH 6.5, 7.0 and or 8.0. At this low storage temperature, all milk samples were stable to fat globule aggregation, creaming, curcumin degradation (37 ºC (21%) > 20 ºC (10%) > 4 ºC (5%). Interestingly, the color of the samples stored at 4, 20 and 37 ºC remained similar to that of the initial samples, but the sample stored at 55 ºC showed significant color fading. The bioaccessibility of the curcumin determined using a simulated gastrointestinal tract model was around 40%, which was attributed to some chemical degradation and binding of the curcumin reducing its stability and solubilization. Overall, the results of this research provide valuable information that will facilitate the design and formulation of curcumin-fortified functional foods with potential health benefits.

DOI

https://doi.org/10.7275/22409583.0

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