Study On Preparation And Purification Of Sterols From The Waste Residue Of Soybean Oil Deodorizer Distillate

Phytosterols are a kind of natural active substances with total hydrophenyl cyclopentane as the back bone,They can reduce the concentration of total cholesterol and low density lipoprotein cholesterol in serum,and effectively prevent cardiovascular and cerebrovascular diseases.Phytosterols exist mainly in free sterols and sterols esters.Soybean oil deodorizing distillate was comprehensively utilized mainly by molecular distillation method in industry.However,phytosterol esters are lost in the waste residue of soybean oil deodorizer distillate(WRSODD)because of their high molecular weight and boiling point.This results in the waste of sterol resources extremely.In this study,the sterols(free and esters)are recovered from the waste residue of soybean oil deodorizer distillate by two methods.One is direct purification of sterol esters,and the other is transesterification sterol esters to free sterols and then separation.Firstly,the quantitative analysis method of sterol esters in the waste residue of soybean oil deodorizer distillate was established.Secondly,sterol esters were purified from the waste residue of soybean oil deodorizer distillate by column chromatography.The purification process was optimized and the sterol esters were characterized.Thirdly,the transesterification of sterol esters in the waste residue of soybean oil deodorizer distillate was catalyzed by chemical method and the transesterification process was optimized.Finally,the free sterols from the waste residue of soybean oil deodorizer distillate transesterification products were separated and purified by two-step crystallization method.The crystallization process conditions were optimized and the purified free sterols were characterized.The main results were as follows:(1)The content of sterol esters,free sterols and total sterol were(51±0.25)%,(8.04±0.06)% and(59.04±0.18)% respectively in the waste residue of soybean oil deodorizer distillate.A comparative study of different methods for the deter mination of sterol esters in the waste residue of soybean oil deodorizer distillate showed that there was a large deviation in the direct quantification of sterol esters.Therefore,the precise quantification of sterol esters in the waste residue of soybean oil deodorizer distillate was analyzed by Reversed-Phase High Performance Liquid Chromatography(RP-HPLC)after saponification to free sterols.(2)Sterol esters from the waste residue of soybean oil deodorizer distillate were purified by column chromatography.The purification process of sterol esters was optimized with the purity and recovery rate of sterol esters as evaluation index.The single factor test was carried out to obtain the optimum purification conditions,which were as follows: the absorbent type of silica gel powder(200-300 mesh),sample volume of 0.5 g,the eluent solvent of a mixture of n-hexane,diethyl ether and glacial acetic acid(95:5:1(v/v/v)),and the ratio of column length to column diameter of 16:1.Under the optimal reaction conditions,the purity and recovery rate of phytosterol esters were(89.90±0.94)% and(96.15±1.49)%.The contents of β-sitosterol ester,stigmasterol ester and campesterol ester were(49.69±0.19)%、(23.19±0.04)% and(16.51±0.28)%,respectively.(3)The transesterification process of sterol esters in the waste residue of soybean oil deodorizer distillate was optimized with the transesterification rate of sterol esters as evaluation index.The single factor and orthogonal test were carried out to obtain the optimum transesterification conditions,which were as follows: The sodium ethanol was selected as catalyst,the ethanol was selected as reaction solvent,the solid-liquid ratio(w/w)was 1:2,the content of catalyst was 7%,reaction temperature of 70 ℃ and reaction time of 60 min.Under the optimal reaction conditions,the transesterification rate of sterol ester was(94.19±0.36)%,the content of free sterols were(54.67±0.18)%,and the content of β-sitosterol,stigmasterol and campesterol in transesterification products were(31.57±0.41)%,(13.26±0.07)% and(11.34±0.66)%,respectively.(4)The free sterols in the waste residue of soybean oil deodorizer distillate transesterification products were refined by two-step crystallization method.The crystallization process of free sterols was optimized with the purity and recovery rate of free sterols as evaluation index.The single factor and orthogonal test were carried out to obtain the optimum crystallization conditions.The first optimal crystallization conditions were as follows: n-hexane was selected as crystallization solution,the ratio of solid-liquid(g/m L)was1:3,crystallization temperature of 8 ℃ and crystallization time of 8 h.Under the optimal reaction conditions,the purity and recovery rate of phytosterol were(72.51±0.51)% and(89.54±0.49)%,the content of β-sitosterol,stigmasterol and campesterol were(42.06±0.61)%,(19.17±0.35)% and(11.29±0.34)%.The secondary crystallization conditions were as follows:anhydrous ethanol was selected as crystallization solution,the ratio of solid-liquid(g/m L)was1:7,crystallization temperature of 8 ℃,crystallization time of 30 min.Under the optimal conditions,the purity and recovery rate of phytosterol were(96.23±0.92)% and(91.95±0.79)%,respectively.The content of β-sitosterol,stigmasterol and campesterol were(56.86±0.50)%,(26.37±0.46)% and(13.00±0.31)%,respectively.(5)The sterol esters purified products and the free sterols purified products were characterized.The results demonstrated that the fatty acids on sterol esters were linoleic acid,oleic acid,palmitic acid,stearic acid and linolenic acid,with the contents of(48.85±0.14)%,(22.25±0.06)%,(19.09±0.05)%,(4.78±0.01)%,(4.72±0.01)%,respectively.The melting temperatures of sterol esters were-57.0 ℃ to-48.8 ℃ and 32.6 ℃ to 66.3 ℃.The thermal decomposition temperature of sterol esters products ranged from 257.5 ℃ to 440.0 ℃.The refined product of secondary crystallization is white powdery solid,while the free sterol crystals are flake.The melting temperature of the purified product of secondary crystallization is-38.6 ℃ to-25.8 ℃,53.2 ℃ to 75.0 ℃ and 134.6 ℃ to 139.8 ℃.The thermal decomposition temperature is 247.3 ℃ to 440.1 ℃.