Preparation And Purification Of Medium-and-Longchain Triacylglycerols Rich In α-Linolenic Acid

Medium and long carbon chain triglyceride(MLCT)is a kind of functional lipid with special nutritional properties and extraordinary physical and chemical properties.Commercial MLCT products have been widely used in food and medicine industry.However,they are all produced by foreign companies.What’s more,almost every MLCT is made from soybean oil which contains a large amount of n-6 polyunsaturated fatty acids.There is little MLCTs rich in n-3 fatty acids.Alpha-linolenic acid(ALA)is one kind of n-3 polyunsaturated fatty acids,which is abundance in vegetable oils such as linseed oil and much cheaper.Moreover,its oxidative stability is better than other n-3 fatty acids,which benefits the preparation of MLCT rich in n-3 polyunsaturated fatty acid.This study is dedicated to explore a simple and convenient process for the preparation and purification of MLCT rich in ALA which can meet the actual production requirements.The main research contents are as follows:1.Medium and long chain triglycerides were prepared from medium chain fatty acid triglycerides and flaxseed oil by sodium methoxide catalyzed chemical transesterification.Quality indexes of the raw materials were determined in order to ensure these raw materials meet the demands.After that,four factors,including substrate ratio,catalyst loading,reaction temperature and reaction time,were optimized.The optimal conditions were as follows:substrate ratio 60%,catalyst loading 0.3%,reaction temperature 50℃,reaction time 15 min.The content of MLCT and diacylglycerol(DAG)were 75.36% and 11.71% respectively.2.A multivariate regression model was established aimed at predicting the two main quality indexes of products under different parameters.After SPSS analysis,it was found that there were multivariate nonlinear relationships between MLCT and DAG content and substrate ratio,catalyst loading,reaction temperature and reaction time.The degrees of fitting and residual test were carried out.The results showed that the coefficient of association of MLCT content and DAG content were 0.914 and 0.933,respectively,and the F value was 676.954 and1119.7,respectively,which was higher than the critical value of F value at the level of p =0.01 and p =0.05.These all indicated that the general equation fitted well.Residuals of the multiple regression equation are normally distributed,which meets the requirements of homogeneity of variance test,meets the assumption of independence.3.The composition and physicochemical characters of these samples before and after transesterification were determined.After transesterification,the content of ALA in product was at a high level which up to 35.36%.There was no significant change in the content of sterol,but the content of tocopherol decreased significantly.The acid value increased to 0.87 mg KOH/g while the peroxide value did not change significantly.In particular,the oxidation induction time was increased from 9.91 h to 11.39 h after transesterification.Chemical transesterification reaction changed the physicochemical characters and composition,which leads to challenges in meeting the requirements of medicinal application.4.The transesterification crude products were refined by silica gel adsorption and silica gel chromatography respectively.adsorption.After silica gel adsorption,DAG content,acid value and peroxide value of the product were reduced to different degrees,but the DAG content was 9.01% and the acid value was 0.54 mg KOH/g,which could not reach the standard of medicinal products.The silica gel column chromatography removed more DAG.The optimaized silica gel chromatography conditions were as follows: 40 g silica gel(200-300mesh),n-hexane/anhydrous ether(5:1),using 500 m L eluant,elution rate at 2.0 m L/min and loading 4 g crude MLCT.Under these conditions,the by-product DAG in the crude product can be almost completely removed,and the DAG content of the product is reduced to 0.07%,reaching the standard of medicinal products,and the product recovery rate is more than 95%.The composition and physicochemical characters before and after purification were determined.Acid value and peroxide value dropped to a very low level after silica gel chromatography,which were 0.04 mg KOH/g and 0.00 g/100 g,respectively.The content of minor componentsdecreased after silica gel chromatography as sterol content was significantly decreased,tocopherol decreased silightly.The main quality indexes of the refined products have reached the standard requirements of medicinal products.To sum up,this study succeeded in preparation and refining medium and long carbon chain triacylglycerols rich in alpha-linolenic acid.The final product riched in MLCT and ALA,and has a low acid value,peroxide value and content of DAG,which basically meets the standard requirements.What’s more it provided a reference for the perapring a new typeof MLCT products.