Effect Of Solid Lipid On Stability Of W/O And W/O/W Emulsion Gel And Photostability Of VB₁₂

W/O emulsions and W/O/W multiple emulsions have been broadly applied in encapsulating and protecting water-soluble functional materials,however,it is thermodynamically instable during storage,i.e.,creaming/sedimentation,flocculation,coalescence and Ostwald ripening,leading to the degradation of functional materials.Emulsifier is the key factor in preventing stable emulsion and the study of emulsion destabilization is necessary,especially the effect of emulsifier molecular structure on the formation of an interfacial film with sufficient strength and further on the emulsion stability is essentially important.The addition of solid fat could form emulsion gel and provide a physical barrier to prevent the emulsion stabilization.Solid fats with different interface properties have varied effects on emulsion stabilization.Solid fats with different interface properties were thus compared in this work and their crystalline properties were adjusted to improve the stability of W/O and W/O/W emulsions.The effect of molecular structure of emulsifier on the stability of emulsion was investigated,and then the stability of W/O emulsion and W/O/W multiple emulsion were further improved by glyceryl monostearate(GMS)and glyceryl tristearate(GTS)respectively.The solid lipid crystallization providing Pickering stabilization and/or network stabilization was investigated,and the protective effect of emulsion gels on the water-soluble functional component VB₁₂ was studied.The main research contents and results were as follows:(1)Polyglycerol polyricinate(PGPR)was used to prepare stable W/O emulsions after the optimization of hydrophobic emulsifiers.The dynamic interfacial properties of PGPR and polyglycerol-2 dioleate at the oil-water interface and their emulsions stability were studied.The results showed that PGPR could quickly reach adsorption equilibrium at the interface after 6compression-expansion cycles.The higher interfacial dilatational viscoelasticity,i.e.,interfacial dilatational elasticity of 5?6 m N/m and interfacial dilatational viscosity of 1?2m N/m,was observed in amplitude and frequency sweep,resisting the influence of external disturbance on the interfacial film and improving the emulsion stability.Polyglycerol-2 dioleate reduced the interfacial tension to 1 m N/m more effectively,however,it took longer time(9cycles)to reach the equilibrium of interfacial film.The interfacial film exhibited pure elasticity in amplitude scanning,and showed a low interfacial dilatational elasticity of 2 m N/m at low frequency,which failed to resist the disturbance of film at low frequency and lead to the instability of emulsion.(2)W/O emulsion gel were prepared using GMS with interfacial activity as the solid lipid.To improve the storage stability,emulsion gels were prepared by optimizing the GMS concentration and cooling rate.And the improvement was observed when stored at 45°C.The polymorphic transitions of GMS crystal were analyzed by XRD and DSC.The changes of GMS crystal network structure were studied by rheometer.And the stability of W/O emulsion gels were studied by LUMi Sizer.Finally,the protective effect of GMS and GTS on VB₁₂was compared.The results showed that the addition of 15%oil phase mass ratio of GMS could not improve the stabilization of emulsion gel during storage.Emulsion gels prepared under two cooling rates kept stable at higher GMS concentration,and the cooling rate insignificantly affected the polymorphic transitions of GMS.However,with the addition of 15%GMS,the emulsions prepared under slow-cooling rate showed faster polymorphic transition,while the emulsions prepared under fast-cooling rate showed stronger crystal network structure under the initial conditions.During the centrifugal stability test,the samples prepared under slow-cooling rate were more stable than those prepared by under fast-cooling rate when stored at 45°C,however,the contrary phenomenon was observed when stored at 25°C.GMS effectively improved the photo-stability of VB₁₂,and the retention rate was larger than 90%after 4 h UV irradiation.GTS accelerated the photolysis of VB₁₂ and the retention rate decreased to 65%after 2 h UV irradiation,which was even lower than the W/O emulsion without solid lipid addition.(3)Polyglycerol-10 myristate(M1001)was selected as the hydrophilic emulsifier,and W/O/W multiple emulsion gels with higher encapsulation efficiency and better dispersion were prepared by optimizing the emulsifier amount,shearing rate,shearing time,GTS concentration and primary emulsion-water ratio.Their protective effect on VB₁₂ was investigated.The results showed that the W/O/W multiple emulsion gel was successfully prepared under optimal condition,i.e.,M1001 added with the external water phase concentration of 1%,a primary emulsion-to-water ratio of 1:2 and dispersed after high-speed shearing at 7000 rpm for 2 min.The addition of GTS effectively improved the protection effect of multiple emulsions on VB₁₂from 16%to 30%,unfortunately,excessive GTS addition could easily lead to the flocculation of droplets and the leakage of VB₁₂.