The Effect Of Emulsification On The Colloidal Properties And Antioxidant Activity Of Oolong Tea Infusion

The process of brewing tea involves a series of physiochemical reactions and interactions between amphiphilic compounds,which lead to the formation of supramolecular structures and micro/nano-particles(MNPs).The dispersion system of tea infusion can be divided into three categories:true solution,colloidal dispersion and coarse dispersion.The micro/nano-particles in tea infusion were partially or completely removed by microfiltration and ultrafiltration method,which directly affected the sensory indexes and free radical scavenging ability.Emulsification,thickening and stabilizer are amphiphilic,it can merging,package,gather and direct effect on the structure and function of micro/nano micelle with heating process,but the interactions between them which affect people's nutrition and health status by means of changing colloid structure in tea infusion remains to be explored.The main results are shown as below:Micro filter can remove large colloidal particles make tea infusion stability;Ultrafiltration can wipe off all micro/nano-particles make colloidal properties completely destroyed.The morphology of tea micro/nano-particles were observed by scanning electron microscope(SEM)and Cryo-Transmission Electron Microscope(TEM),the morphology of tea MNPs present spheroidal and the particle size was similar with the particle size which were determined by Dynamic light scattering.The main substance in the tea infusion is the existence of wandering,the proportion of the combination state and the wandering state is 1 to 4.The tea infusion was determined by three kinds of antioxidant methods(DPPH,FRAP,ORAC).Results show that ORAC activities of tea infusion was declined by ultrafiltration(279 to 231?molTE/g)whereas no difference was found in FRAP and DPPH determinations;The antioxidant capacity may be related to the colloid structural changes of the tea infusion.The colloidal properties of the tea soup were significantly changed by adding emulsifier in the tea infusion with mechanical homogeneity.Mechanical homogenization(MH),with or without casein,lecithin,and?-cyclodextrin as emulsifiers,altered the colloidal micro/nano-particles(MNPs)of tea by significantly increasing the average hydrodynamic diameter from 318±15 nm to 432±29 nm(mechanical alone)and 719±83nm(casein,0.1‰W/V),and ?-potential from-25.6 mV to-23.5mV.The correspondent bioactivities of those MNPs,in which the antioxidant tea polyphenols may interact with other compositions,were accessed in terms of antioxidant activities,namely oxygen radical absorbance capacity(ORAC),Ferric reducing antioxidant potential(FRAP)and DPPH radical scavenging assay.The emulsification significantly increased ORAC activities of tea infusion,e.g.from 279 ?M TE/g to 414 ?M TE/g of ?-cyclodextrin,whereas no difference was found in FRAP and DPPH determinations.It implies the MNPs in tea infusion have antioxidant activity,which can be manipulated by emulsification via modifying the physiochemical properties of hydrocolloidal particles.The micro/nano-structure transformation occurred during beverage processing can possess important influences on its bioactivity,therefore should be handled with extra caution.