Emulsion-based delivery systems to improve gut and brain bioaccessibility of curcumin in relation to Alzheimer’s disease prevention : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Palmerston North, New Zealand
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Date
2023
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Massey University
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Abstract
Medium chain triglycerides (MCT) from coconut oil, omega-3 polyunsaturated fatty acids from fish, phospholipids from dairy milk, and curcumin from turmeric all have been recognized for their anti-inflammatory and antioxidant properties. Curcumin is also a potential candidate for Alzheimer’s disease (AD) prevention; however, curcumin is poorly bioavailable unless emulsified. The milk fat globule membrane (MFGM) has natural emulsifying properties. I aimed to design an emulsion-based delivery system containing functional oils to encapsulate and deliver curcumin to the brain. I evaluated three commercial MFGM components with coconut and fish oils to produce emulsions with improved curcumin bioavailability. The emulsion structures were characterised by particle size, zeta-potential at the surface, microscopic structure, curcumin loading efficiency, and phospholipid distribution. All emulsions showed stable to particle size changes over 40 days at 4°C. Emulsion particle size decreased significantly with increasing concentrations of emulsifier, and presented negative zeta-potential varying from -50 to -20 mV, with the MFGM fractions creating significantly different charges and curcumin loading efficiency based on phospholipid and protein composition. All MFGM fractions efficiently created stable emulsions with small particle size and encapsulated curcumin. After simulated in vitro digestion, the emulsion with the highest phospholipid content had significantly higher curcumin bioaccessibility compared to the others. Fresh and digested emulsions and their components were assessed in the BE(2)-M17 neuroblastoma cell model for amyloid-β (Aβ) toxicity. Emulsions composed of both fish and coconut oils provided greater protection against Aβ toxicity compared to coconut oil alone. Curcumin was transported in vivo across the intestinal wall to the bloodstream and across the blood-brain barrier to the brain in rats fed all curcumin delivery formats. The kinetics of curcumin in blood and brain varied depending on the emulsion format. MFGM emulsions significantly reduced the curcumin and its metabolites peak time in blood and brain compared to the commercial curcumin preparation Meriva®, and all emulsions improved overall curcumin bioavailability and accumulation in the brain compared to free curcumin. A novel ex vivo approach using rat plasma samples directly in the neuroblastoma cell model requires further optimisation but demonstrated a significant interaction between gender and treatment on cell viability.
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Emulsions, Curcumin, Milkfat, Alzheimer's disease, Research