Development Of Novel Catechin Esters And Evaluation Of Their Antioxidant Activity

Two novel catechin esters,P-sitosterol acylated catechin and L-cysteine acylated catechin were synthesized in this work applying(+)-catechin as raw material.The lipid-oxidation inhibitory effect of these compounds was investigated by a combination of O/W,W/O,liposome and low density lipoprotein(LDL)systems and the related mechanism was discussed.Besides,a model for the evaluation of the transmembrane properties of(+)-catechin and other polyphenols via passive diffusion was established employing laccase liposome to simulate biofilm.The relative transmembrane rate of five polyphenols was also measured.The main results of this work were summarized as follows:1)?-sitosterol was covalently conjugated with(+)-catechin by a succinic anhydride spacer to prepare the ?-sitosterol acylated catechin.The purity of product was around 79%as determined by UPLC.Moreover,the molecular structure of P-sitosterol acylated catechin was characterized by a combination of ESI-MS,FT-IR,and NMR.2)The lipid-oxidation inhibitory activity of the samples in a W/O emulsion decreased with the trend:?-sitosterol acylated catechin>TBHQ>(+)-catechin>(3-sitosterol,as suggested by the decay of a lipophilic fluorescence probe,DAF;The lipid-oxidation inhibitory activity of the samples in an O/W emulsion decreased with the trend:P-sitosterol acylated catechin? TBHQ>(+)-catechin>?-sitosterol.By using the retention rate of ?-carotene as an indicator;the lipid-oxidation inhibitory activity of the samples in a liposome model decreased with the trend:BHT>?-sitosterol acylated catechin>(+)-catechin>?-sitosterol,as determined by the content of the secondary phospholipid oxidation product TBARS.In the system of emulsion,the antioxidant activity of P-sitosterol acylated catechin in these model was higher than that of(+)-catechin,which was closely related to the higher lipophilicity of ?-sitosterol acylated catechin and therefore their higher distribution radical-scavenging capacity at oil-water interfacial.3)L-cysteine acylated catechin was synthesized by esterification of the carboxylic group in L-cysteine with the hydroxyl group on 3 position of ring C of(+)-catechin.The purity of the product was determined to be above 99%by UPLC.The molecular structure of the product was further analyzed by ESI-MS,FTIR and NMR,respectively.4)The DPPH radical-scavenging activity of the samples decreased with the trend:(+)-catechin>?-sitosterol acylated catechin>TBHQ? BHT>L-cysteine;The lipid-oxidation inhibitory effect of the samples in liposome model decreased with the trend:L-cysteine acylated catechin ? TBHQ? BHT>Vc>(+)-catechin>L-cysteine,as determined by the content of TBARS;the lipid-oxidation inhibitory effect of the samples in W/O emulsion decreased with the trend:L-cysteine acylated catechin>TBHQ>(+)-catechin>L-cysteine>BHT>Vc,using the retention rate of ?-carotene as an indicator;the lipid-oxidation inhibitory effect of the samples in LDL model decreased with the trend:L-cysteine acylated catechin? Trolox>(+)-catechin>ferulic acid,as suggested by the content of TBARS;the oxidation induction time of bulk soybean oil containing different antioxidants decreased with the trend:TBHQ>L-cysteine acylated catechin>BHT.In general,the lipid-oxidation inhibitory capacity of L-cysteine acylated catechin was higher than or comparable with that of TBHQ or BHT,which revealed their potential application in food industry.5)An in vitro model for the transmembrane properties of polyphenols via passive diffusion was established.Laccase liposome was prepared using film hydration method to simulate biofilm and the unencapsulated Laccase was inactivated by KF.The polyphenols passed through the liposome bilayer via passive diffusion and reached the inner aqueous core of liposome where they were oxidized by the encapsulated laccase to produce quinones.The relative transmembrane rate through passive diffusion of polyphenols could be determined by monitoring the time-dependent absorbance of the quinones at 400 nm The relative transmembrane rate of polyphenols such as(+)-catechin,EGC,catechol,pyrogallic and dopamine hydrochloride were determined to be 6.32,12.7,9.65,15.77 and 10.36,respectively,according to the established model.This model would contribute to the investigation of the cellular adsorption of polyphenols.