Effects Of Sterols On The Properties Of Phosphatidylcholine Liposome

Liposome, whose bilayer structure was similar to biomembrane, was a microsphereusing phospholipid as membrane materials. It can simultaneously embed hydrophilic andhydrophobic substances, thereby improving stability and drug loading rate. However, becauseof the existence of large amouts of unsaturated aliphatic acid, phospholipid was easilyoxidated and its stability was affected. Therefore, the studying on how to improve stability ofliposome is an urgent problem needed to be solved. In the preparation process of liposome,cholesterol was usually added to improve liposome properties. However, with people’sprompting demands of health, food with low cholesterol was needed increasingly. Thus a newsubstance was required to replace cholesterol.In our research, phosphatidylcholine was used as a raw material to prepare liposome, andthe effects of cholesterol and phytosterol on properties of liposome membrane was studied.Meanwhile, the feasibility of phytosterol substituting for cholesterol was also discussed,providing theoretical foundation for application of liposome in food industry.Particle size and distribution of liposome were measured in this paper by dynamic lightscattering method. The results showed that particle size of liposome increased as sterolconcentration increased. When the concentration increased to50%, particle sizes of liposometreated by mixed plant sterol, β-sitosterol, cholesterol and stigmasterol increased by19.8%,21.0%,23.0%and34.3%respectively. From the uniformity of particle size distribution,liposome treated by β-sitosterol was found to have best uniformity. From the measurement of30days’ variation of particle sizes, it was found that the optimal concentrations of mixedplant sterol, β-sitosterol, cholesterol and stigmasterol were25%,15%,50%and50%respectively. After being stored for30days, particle sizes of liposome increased by10.7%,15.6%,16.9%,23.0%respectively. Liposome patterns were observed by TEM, and it wasfound that liposome treated by mixed plant sterol and β-sitosterol had legible border andregular pattern.Contents of malondialdehyde in the liposome with different storage times were alsotested for the determination of study the oxidation stability. The results showed that, in termof the stability of liposome the optimal concentrations of mixed plant sterol, β-sitosterol,cholesterol and stigmasterol were50%,50%,25%and5%respectively. The absorbency ofmalondialdehyde at A532increased by0.51,0.68,1.12,2.06times after30days. These resultsindicates that liposome treated by mixed plant sterol and β-sitosterol has higher oxidationstability.In this paper, effects of cholesterol and phytosterol on micro-enviro nment of liposomewere studied by fluorescence spectra. Results of pyrene fluorescence probe method indicatedthat micropolarity of liposome membrance decreased with the increasing concentration ofsterol. And when the concentration increased to50%, mixed plant sterol, β-sitosterol,cholesterol and stigmasterol decreased by7.33%,7.01%,6.03%,5.09%respectively. Theseindicated that molecular layers of mixed plant sterol and β-sitosterol were combined more tightly. Results of DPH fluorescence probe method showed that cholesterol had the bestregulating effect for membrane fluidity, followed by mixed plant sterol, β-sitosterol andstigmasterol.Finally, the best preparation conditions of VEliposome were studied by testing variationsof embedding rate and particle size of VEliposome. The optimal condition was as follows:3times of ultrasound,5min/time, mass ratio of VEand phospholipid1:20. Based on the aboveresults, envelop rate and retention rate of different sterol liposome were compared. The resultsshowed that envelop rate and retention rate of mixed plant sterol were the highest, reached to82.7%and88.1%respectively. After comparision of the effects of different kinds of sterol onparticle size, potential, oxidation stability, micropolarity, fluidity of VEliposome, it was foundthat β-sitosterol and mixed plant sterol had the better effect on the size distribution stabilityand oxidation stability of VEliposome. Therefore, substituting β-sitosterol and mixed plantsterol for cholesterol is viable.