Solubilization Of Phloretin By Steviol Glycosides

Phloretin(PT)is a dihydrochalcone plant flavone with glucose absorption inhibition and C6-C3-C6 as the skeleton.PT exhibits poor water solubility(20 ?g/mL)due to its planar structure,intramolecular ?-? action,lattice energy and intermolecular hydrogen bonding.Steviol glycosides(STE),which are widely used as sweeteners in food industry,are the mixture of tetracyclic diterpenoids based on steviol.As for its molecular structure,it is a Bola type amphiphilic molecule with two hydrophilic ends and intermediate hydrophobic structure.It can be served as a surfactant to solubilize hydrophobic substances.In this paper,PT was solubilized by ST based micelle(MC)and solid dispersion(SD),respectively.The two solubilization systems were optimized firstly.The solubilization mechanisms and the difference of solubilization ability of these two systems were investigated.The changes of in vitro release,absorption and glucose absorption inhibition before and after solubilization were also investigated.The combination of PT and STE can provide some theoretical guidances for the food development for diabetic patients.The main conclusions of this paper are as follows:1.Single factor experiment,Box-Behnken response surface and molecular dynamics simulation were used to develop and optimize STE-PT MC.and STE-PT SD.The results show that the difference of solubility parameters between stevioside(main component of STE)(14.346(J/cm3)1/2)and PT(17.455(J/cm3)1/2)was only 3.1(J/cm3)1/2,so STE is a suitable material for PT solubilization.For STE-PT MC,30 mg of PT can be completely dissolved in 10 mL water with 103 mg/mL STE,30 min of stirring and 80?,while 30 mg of PT can be completely dissolved in 10 ml water without heating and with 50 mg/mL STE in STE-PT SD.In addition,due to the self aggregation of Rebaudioside A(RA),the increase of RA content in STE is not conducive to the solubilization of these two systems.2.STE-PT MC/SD were characterized by pyrene fluorescence probe,molecular mesoscopic simulation,FTIR,DSC,SEM,TEM,particle size analysis and X-ray diffraction.The solubilization mechanism and the difference of solubilization ability were explored.The results show that there was no chemical reaction in the two solubilization systems.For STE-PT MC,STE can self assemble into a spherical micelle structure with the particle size of 5 nm,and encapsulate PT in hydrophobic core to increase its solubility.For STE-PT SD,PT is completely dispersed in STE with an amorphous state after solid dispersion process,which allows PT dissolve into water with less external energy and thus significantly improves the solubility of PT.In addition,there were not only small micelles with particle size of 4-5 nm but also relatively large micelles(500-700 nm)in STE-PT SD water solution.This phenomenon combined with the amorphous state may be the potential reason for the high solubilization ability of STE-PT SD.3.The solubilization behavior and dispersion state of PT in the two systems were proposed according the changes of fluorescence and UV absorption spectra of the interaction between BSA and PT before and after solubilization.The results show that most of PT was encapsulated by STE self-assembled micelles in STE-PT MC,which put an obstacle in the interaction between PT and BSA.In STE-PT SD,the interaction of PT with BSA was strong,indicating that most of PT with amorphous state can directly dissolved in water and only a small amount of PT was encapsulated by STE micelles.4.The in vitro digestion stability,absorption,release rate and release kinetics of PT before and after solubilization were investigated using the static in vitro digestion,single-layer Caco-2 cell and release model,The results show that STE-PT MC and STE-PT SD exhibited good solubilization stability in each digestive juice,and the release rates and cumulative release amounts of PT from STE-PT SD were slightly higher than that from STE-PT MC after 36 h.In addition,the release rates of PT in simulated gastric juice(SD:53.84%,MC:41.37%)were higher than that in simulated intestinal juice(SD:21.05%,MC:24.37%)due to the low solubility of PT in acid release medium.The release kinetics of PT in STE-PT SD was best fitted with the Ritger-peppas equation(n<0.5),suggesting that the release of PT from STE-PT MC is concentration dependent and belongs to Fickian diffusion,which is in accordance with Fick's first law.However,the release of PT from STE-PT MC was better fitted with the first-order kinetics equation due to the encapsulation and transport of STE micelles,which belongs to non Fickian diffusion.Finally,the absorptivity and glucose absorption inhibition of PT increased significantly after solubilization,and the effects of STE-PT SD were relatively more significant.