| Pickering emulsions are the emulsions which are stabilized by solid particles instead of surfactants. Due to their wide range of application in foods, pharmaceuticals and cosmetics industries, Pickering emulsions are considered as an important formulation and are intended to be used as a delivery system for bioactive compounds. The solid particles for the stabilization of Pickering emulsion can be organic such as polymer latex or inorganic, such as silica and clay particles. However, particles from natural polymers have been shown of great advantage over the rest, and therefore, polysaccharide the most abundant polymer in nature is one of the most important selections which retain outstanding physical and biological properties. In this context, chitosan(CS) the second most abundant biopolymer in nature next to cellulose which has unique characteristics of biodegradability, biocompatibility, bio-adhesion and non-toxicity, is widely used for the preparation of these nanoparticles(NPs). A series of methods are used for producing stable CS NPs for different applications. Here, we prepared the CS NPs by two different methods i.e pH induced CS NPs and by ionic gelation technique that involves the ionic interactions between the positively charged primary amino groups of CS and the negatively charged groups of poly anion, such as(TPP). The preparation of nanoparticles, Pickering emulsion, and its application as a delivery system for curcumin are discussed.1. pH induced chitosan nanoparticles for the preparation of Pickering emulsion were prepared by adjusting pH of the chitosan solution. At pH <6.5, chitosan was soluble in water and hence no particles were formed. However, with increasing pH >6.5 by the addition of NaOH solution, chitosan became insoluble in water and thus chitosan nanoparticles were obtained. The Pickering emulsion was prepared by homogenizing the water phase(chitosan nanoparticles) and Medium chain triglyceride(MCT) as an oil phase. The emulsion prepared at pH 7 was stable for 3 months, whereas the emulsion formed at pH(<6.5) was not stable and demulsified after a couple of days. The ratio of oil to water also showed positive influence on the emulsion stability and the optimized ratio was found to be less than 2:1. In order to study the influence of the salt contents(NaCl and CaCl2) on the demulsification performance of the emulsion, salts solution with different concentrations(0-200 mM) of either Na Cl or CaCl2 were added to the emulsions after preparation and the pH was adjusted at 7. Increasing salt concentration also caused increase in emulsion droplet, which was one of the reasons for the increase in the droplet size after the emulsification demulsification cycles. The emulsion also showed long term stability after storage at room temperature for 3 months.2. The preparation of Chitosan-tripolyphosphate(CS-TPP) nanoparticles stabilized Pickering emulsion was optimized as a delivery system for curcumin. The CS-TPP nanoparticles(NPs) were prepared by the ionic gelation techniques between CS and TPP. The effect of preparation conditions, storage time, pH and salt on the stability of Pickering emulsion was evaluated. CS concentration showed positive effect on the emulsion stability. The emulsions droplet size changed greatly over a period of storage time, when the CS concentration was 0.2 wt %. Also the emulsion was not very stable when different emulsifier(CS-TPP NPs) concentration was used, although the CS concentration was 0.5 wt %. The emulsions showed good long term stability against aggregation at pH values(3, 6 and7), NaCl and CaCl2 concentrations(0-200mM), at 0.5 wt % CS and 0.1 wt % TPP concentration. Then curcumin was successfully encapsulated in the prepared Pickering emulsion system that maintained good stability of the encapsulated curcumin. The release profile of curcumin from the Pickering emulsion showed a sustained release over extended period of time.3. The influence of different lipid-based formulations(Pickering and nanoemulsions) and their droplet size on curcumin encapsulation and bioaccessibility, as well as on its anti-oxidant activity was investigated. Oil-in-water Pickering and nanoemulsions were prepared with either medium chain triglyceride(MCT) or corn oil as long chain triglyceride(LCT). An in vitro model simulating mouth, gastric and small intestine digestion conditions characterised rate and extent of lipid phase digestion. A centrifugation method determined fraction of curcumin released into mixed micelles after digestion(bioaccessibility). The digestion rate decreased in order NMCT > NCO>PMCT>PCO, where N, P, MCT and CO are abbreviations for nano, Pickering, medium chain triglyceride and corn oil respectively. The bioaccessibility of curcumin decreased in the order NCO>NMCT>PCO>PMCT. Similarly, the radical scavenging activity before digestion decreased in the order PCO>NCO>PMCT>NMCT, while after digestion the extent decreased NCO>PCO>NMCT>PMCT. Thus as compared to free curcumin, the encapsulated curcumin showed higher radical scavenging activity, which confirmed the protective effect of the emulsion systems on the antioxidant activity of curcumin. |
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