| Egg yolk phospholipids contain two main active components,phosphatidylcholine(PC)and phosphatidylethanolamine(PE).Egg yolk phospholipids have antioxidant,hypolipidemic,immunomodulatory,hepatoprotective and memory-improving properties and are widely used in medicine,food,cosmetics and feed.The composition of egg yolk phospholipids is required for different applications of phospholipids.It is important to study the changes in the content of PC and PE,the main active components of high purity egg yolk phospholipids,during the extraction and purification process to obtain egg yolk phospholipids with a certain range of PC/PE ratio.In this study,the extraction conditions of PC and PE,the active components of egg yolk phospholipids,were optimized by low-temperature freezing crystallization and n-hexane-acetone precipitation methods respectively.The effects of different factors on the regulation of PC and PE components of egg yolk phospholipids by alumina were investigated and their patterns were discussed,and the adsorption behaviour and mechanism of alumina on PE components of egg phospholipids were elucidated.The main research contents and results are as follows:The extraction of PC and PE from egg yolk by low-temperature freezing crystallization was investigated and the extraction conditions were optimized by response surface methodology.Based on the results of the single-factor experiments,the optimum process parameters were obtained by the response surface methodology:anhydrous ethanol as solvent,1:4(g/m L)material-to-liquid ratio,12.5 h freezing time,-25℃freezing temperature and 96%ethanol by volume.The volume fraction of ethanol was 96%.The total yolk phospholipid PC and PE content was 85.55%,of which 74.38%was PC and 11.17%was PE,and the yield of yolk phospholipids was 10.25%.The extraction conditions for the extraction of PC and PE,the active fractions of egg yolk phospholipids,were optimized in the n-hexane-acetone system using RCEYP egg yolk powder as raw material and the total content of egg yolk phospholipids PC and PE as the investigated index.According to the results of the response surface analysis of variance,freezing time had the greatest effect on the total content of PC and PE,followed by freezing temperature and the n-hexane-acetone solvent ratio.The optimum extraction conditions were as follows:n-hexane-acetone solvent ratio of 1:6(v/v),freezing time of 11.3 h,freezing temperature of-19°C,material-liquid ratio of 1:4(g/m L),acetone washing five times,resulting in high purity yolk phospholipids with PC content of 81.12%and PE content of15.04%,and the yield of yolk phospholipids was 12.8%.The factors and patterns influencing the regulation of PC and PE active fractions in egg yolk phospholipids by alumina were investigated.The selectivity of alumina for PE among the five solvents was as follows:methanol>ethanol>petroleum ether>n-hexane>trichloromethane.When ethanol was used as the solvent,the recovery of egg yolk phospholipids,PC recovery and PC content were higher,and alumina had better adsorption to PE,and ethanol was a safe and non-toxic solvent,so ethanol was chosen as the solvent.The PC/PE ratio decreased with the increase of phospholipid concentration and adsorption temperature,and the PC/PE ratio increased with the increase of adsorption time and alumina addition.When anhydrous ethanol was used as the solvent,the phospholipid concentration was 5 mg/m L,the adsorption temperature was 20℃,the adsorption time was 40 min,and the ratio of egg yolk phospholipid to alumina was 1:10,the high purity PC with 94.1%was obtained by regulation,the PC recovery was 45.97%,and the PE content was 0.46%at this time.The kinetic study of PE adsorption by alumina from mayonnaise phospholipid/anhydrous ethanol solution showed that the fitted secondary kinetic equation fitted the PE adsorption process of alumina better,with a correlation coefficient R~2of 0.9842,and the fitted secondary kinetic model could truly reflect the relationship between PE adsorption amount and adsorption time.The thermodynamic study of PE adsorption by alumina from egg yolk phospholipids/anhydrous ethanol solution showed that the Langmuir model was a better fit than that of the Freundlich model for the thermodynamic process of PE adsorption by alumina(correlation coefficient R~2≥0.9932).The maximum theoretical adsorption of PE decreased from 32.1337 mg/g to 29.9312 mg/g when the adsorption temperature was increased from20°C to 60°C.The process was spontaneous asΔG<0.The adsorption efficiency of PE adsorption by alumina can be improved by lowering the temperature fromΔH<0 andΔS<0.The adsorption effect of alumina on PE at 20°C is better than that at 30°C and 40°C,and the adsorption temperature of 20°C is favourable for the adsorption of PE by alumina in industrial production. |
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