The effect of different Formulation Parameters on The in vitro release of the (-)-EpiGallocatechin Gallate (EGCG) from concentrated w/o emulsions

Abstract

Green tea catechins (GTCs) and caffeine, major constituents of green tea were extracted from ground powder of green tea leaves (Camellia Sinensis L.) by using 80+-1 ℃ de-ionized water with and without dichloromethane solvent extraction. Freeze-dried green tea extracts (FD-GTE) obtained from freeze-drying technique were determined their GTCs contents, i.e. Epigallocatechin (EGC), Epigallocatechin gallate (EGCG), Epicatechin (EC), Epicatechin gallate (ECG) and caffeine by reversed phase-high performance liquid chromatography analysis. Total yields of FD-GTE residues obtained from both extraction procedures are not significantly different (p < 0.05). Content of total GTCs obtained from the extracts with dichloromethane is significantly higher than the one without dichloromethane extraction (p < 0.05). As well as, caffeine content of extracts with dichloromethane shows significantly lower extent when compared with the one without dichloromethane extraction (p < 0.05). Without significant effect on the total yields of FD-GTE, the dichloromethane, therefore, could be effective solvent for removing caffeine from the hot water extraction of green tea leaves. Formulations of concentrated water in oil (w/o) emulsions (CEs), containing 2.25% (w/w) of FD-GTE with 84, 86 and 88% dispersed phase (% DP) and 3% of four different emulsifiers (sorbitan, silicone, mixed and glucoester), were prepared to study the effect of formulation parameters on the in vitro release of EGCG on synthetic polysulfone membrane. The concentrations of the emulsifiers do not have a considerable effect on the release of EGCG. Among the four emulsifiers, the mixed emulsions are the only one that gave a considerable faster release of EGCG over 48 h. Furthermore, they allowed the unstable products and could not perform the polyhedral droplets of all ranges of % DP. This faster release could be attributed to the presence of waxes, which give a more rigid oil film. This rigidity could be responsible for an earlier breakage of the film upon application thereby causing a more rapid release of EGCG. Results suggested that the release characteristics of the unstable CEs (the mixed emulsions) depend mainly on their stability due to the rigidity of interfacial films of water droplets. The droplet diameter decreases and the apparent viscosity increases with the % DP increasing. The shape factor may play an important role on the release of EGCG from stable CEs. With 88% DP, the droplet shape of all stable CEs, except for the mixed type provided the polyhedral structure of water droplets. Moreover, they allowed very stable products with the extreme viscosities. The flux of these systems could be correlated with the structure of water droplet. The polyhedral droplets could retain the release of drug from CEs, containing large amount of water dispersed phase, by self diffusion of water between adjacent droplets. Therefore, the CEs, which possess the polyhedral structures, would prolong the release of drug from the system.