| Epigallocatechin gallate(EGCG) is a kind of natural antioxidant with high water solubility. EGCG has been reported to have various demonstrated health-beneficial activities, including strong antioxidant activity, anti-inflammatory, antitumor, prevention of cardiovascular diseases, neurodegenerative disease, anti-aging and many others. It has already been widely used in pharmaceutical, cosmetic and food fields. However, the application of EGCG in actual production was limited due to its low stability during storage or digestion and its poor intestinal absorption. Using formulation strategy to encapsulate sensitive compounds is considered one feasible approach to improve the stability and oral bioavailability of EGCG. Niosomal system has been suggested to be a promising nanoparticle delivery system in various fileds due to its capacity to protect compounds during storage and digestion, release drugs in a controlled and sustained manner, and its advantages of biodegradability, biocompatibility, and nontoxicity. This thesis is intended to encapsulate EGCG via niosomes, for enhancing its stability and bioavailability.EGCG encapsulated niosomes were formulated using nonionic surfactants and cholesterol. According to the single factor experiments using mean particle size, polydispersity index(PDI) and entrapment efficiency(EE %) as test index, we optimized the operation conditions. The results showed that the optimum preparation conditions were: preparation method was ethanol injection method; wall material consists of Tween60 and cholesterol; ratio of cholesterol to Tween60 was 1:2; hydration time was 30 min; hydration temperature was 50 oC. Under the optimal conditions, the encapsulation efficiency was(76.43±0.76) %, drug loading was close to 9%, mean size was between 60~80 nm and PDI was below 0.2. Moreover, the morphology observed through TEM was unilamellar and the diameter was found to be well correlated with the results obtained from dynamic laser light scattering(DLS) measurements.The release characteristics, digestion characteristics and biological activities of EGCG encapsulated niosomes were evaluated. EGCG loaded niosomes exhibited a relatively good sustaining release of EGCG, for the release rate was reduced from 90% to 14.7% under physiological conditions after 24 h dialysis, compared to the control group EGCG solution. During digestion, the results of the retention rate of EGCG, and viarations in particle size showed that EGCG loaded niosomes were relatively stable during SGF incubating. Meanwhile, retention rate of EGCG after encapsulated were increased from(3.16±1.68) % to(49.42±2.4) % during SIF incubating, indicating that niosomes have a protective effect on EGCG to a certain extent in the gastrointestinal tract. The results of chemical antioxidant activities assays during digestion demonstrated that niosomes inhibited the reduction of antioxidant activity of EGCG, showing the outstading protection effect to EGCG. In order to verify the in vivo bioavailability of EGCG loaded in niosomal system, cell antioxidant activity(CAA) assay and cellular cytotoxicity(MTT) assay had been designed to demonstrate it. Data showed that the EC50 value of EGCG was reduced from 10.395 μg/m L to 6.908 μg/m L, and the IC50 value of EGCG was reduced from 45.24 μg/mL to 35.35 μg/mL, indicating that EGCG after encapsulated display more powerful biological activities.The results of storage experiment of EGCG loaded niosomes showed that the particle size was kept around 60 nm in one month, and the retention rate was(65.42±3.18) %. EGCG niosomes were added to a simulated beverage system. The optimal pH of simulated beverage system was evaluated, and the highest retention rate of EGCG was got at the pH of 4.5. The influence of lighting and temperature to the storage stability were also investigated. It was found that the retention rate of EGCG was increased from(13.61±4.16) % to(74.02±4.16) % while being kept away from the light at temperature of 4 oC, compared to the control group EGCG solution, and the browning reation was inhibited via niosomal encapsulation. |
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