Design,Preparation And Properties Investigation Of Functional Esterified Gallic Acids

Gemini gallate(GG)interfacial antioxidant and polyethylene glycol methyl ether gallate(GAP)protein carrier enhancers were developed through derivatization of gallic acid.Antioxidant activity as well as the mechanism of GG in the O/W emulsion and the stability and digestion of GAP-zein-curcumin were evaluated.The main results were described as follows:(1)A semi-automatic purification system based on silica gel prepacked column and peristaltic pump was developed for the purification of the dodecyl gemini chain,and the mono gallate(MG)as well as gemini gallate(GG)were prepared by Steglich esterification.Upon optimization of the synthesis of dodecyl gemini chains,it was difficult to purify and separate the products catalyzed by zinc chloride,though its catalytic effect was great.Therefore,we finally prepared the dodecyl gemini chains according to the previously established synthesis condition(potassium hydroxide as catalyst and DMSO as solvent)but optimized the purification protocol.A peristaltic pump purification system with silica gel precolumn was developed.The pumping speed of petroleum ether was 16.5 m L/min and ethyl acetate was 3 m L/min.Then the resulting product was coupled with a protected gallic acid,and finally deprotected by hydrated hydrazine.MG was also synthesized to compare with GG.(2)DPPH radical scavenging and ORAC examinations demonstrated that both MG and GG retained the antioxidant activity of gallic acid,and the antioxidant capacity of MG and GG was directly proportional to the molar ratio of their galloyl groups.GG exhibited stronger antioxidant activity than MG in O/W emulsion,and the difference was even more pronounced when reducing the amount of emulsifier.As the amount of emulsifier was at its critical micelle concentration(CMC)value,the antioxidant activity ratio of GG and MG was 5:1,which was significantly higher than the galloyl molar ratio of 2:1.The mechanism study indicated that the remarkable antioxidant activity of GG could be ascribed to the interfacial self-assembly behavior of the unique gemini structure.The gemini antioxidants may make it easier for accumulating in the interfacial layer,thus increasing their interfacial concentration,which is ultimately reflected in the difference of antioxidant activity.(3)Polyethylene glycol gallate(GAP)was designed and prepared through Steglich esterification according to the condition optimized in the synthesis of triethylene glycol gallate.The optimized molar ratio of gallic acid: polyethylene glycol monomethyl ether:DCC: DMAP was 1.5:1:1.5:0.1.Purification was performed by gradient precipitation with a volume ratio of 3:1 ? 1:4 ? 1:0 of petroleum ether and ethyl acetate.(4)GAP was applied to enhance encapsulation capacity of zein exemplified by loading of curcumin.It was revealed that the encapsulation efficiency of the nano-solution with GAP was significantly improved.When the mass ratio of GAP,zein and curcumin was 24:8:1,the encapsulation rate of curcumin was 91.3%.The encapsulation of curcumin in GAP-zein-curcumin particles was confirmed by FT-IR spectroscopy,fluorescence spectroscopy,DSC and laser confocal microscopy.Compared with the zein–curcumin composites,the GAP-zein-curcumin particleshad better stability and higher bioavailability in simulated gastrointestinal digestion.When the mass ratio of GAP,zein and curcumin was 60:20:1,the bioavailability of curcumin was about 5?6 times than that of zein-curcumin composites.