Green Preparation And Characterization Of Oligoglycerol Esters Of Fatty Acids

Oligoglycerol esters of fatty acids(OGE) are an important kind of polyglycerol esters of fatty acids(PGE) which have been widely used as emulsifiers in food, medicine and cosmetic industry. This paper presents the study of green preparation and characterization of OGE, provide theoretical reference for synthesis of high quality OGE products.Firstly, the synthesis of oligoglycerol was investigated using strongly acidic cationic exchange resin by ring opening reaction of glycidol with glycerol. The reaction conditions studied include reaction temperature, reaction time, type and amount of catalysis, and the molar ratio of glycerol to glycidol. Orthogonal test was applied to optimize the reaction parameters, and the average yield of oligoglycerol was 68.83% under the optimum conditions obtained. With a further purification by molecular distillation, the oligoglycerol product obtained achieved a purity of 93.07%.Then, OGE was prepared by the esterification of oligoglycerol with linoleic acid in a solvent free system using Lipozyme 435 as the catalyst. Single factor experiments and response surface methodology were employed to optimize the reaction parameters. The experimental efficiency of esterification was 95.82% under the optimum conditions obtained. The process was scaled up in a pilot bubble column reactor(BCR), and the catalytic stability of Lipozyme 435 was also studied in this reaction system. The results show that the BCR obtained higher reaction efficiency than that of the traditional mechanical stirring reaction kettle. And the enzyme maintained 98.2% of the relative activity after 10 batches of reaction in the BCR, which greatly reduce the cost of enzyme catalytic reaction. Therefore BCR is more suitable for high viscosity of heterogeneous enzymatic catalytic reaction system.Next, OGE was prepared by benzene sulfonic acid catalytic the reaction of glycidyl and monoacylglycerol, the effects of the substrate molar ratio, catalysis dosage, reaction temperature and reaction time on the yield of OGE were investigated. The reaction conditions were optimized by orthogonal test and the average yield of OGE was 62.59% under the optimum conditions obtained. Then the product was purified by molecular distillation, and the purity of OGE can reach 91.45% with the major ingredients were oligoglycerol monoesters. Compared with the monoacylglycerol, it has stronger hydrophilic and better emulsifying performance, which can be used as the hydrophilic emulsifier in food, cosmetic and medicine industry.Finally, diglycerol esters of fatty acids(DGE) synthesized by Lipozyme 435 were isolated and purified by the thin layer chromatography(TLC) and silica gel column chromatography. The composition of DGE was analyzed and identified by high performance liquid chromatography(HPLC) and ESI MS, and further structural analysis of the purified products was obtained by 1H and 13 C NMR. The high purity of tri, di and monoesters of diglycerol linoleic acid were recovered using gradient elution with different volume ratios of chloroform/acetone/methanol(96/4/0, 95/3/2, 96/4/5, respectively). In addition, the effect of DGEs with different degree of esterification on the crystallization behavior of diacylglycerol(DAG) has also been investigated by the analyses of solid fat content(SFC), differential scanning calorimetry(DSC), polarized light microscopy(PLM) and X ray diffraction(XRD). The results revealed that the addition of 0.5 wt% DGE can effectively retard the crystallization of high melting DAG by inhibiting the nucleation process and delaying the crystal growth, while no significant effect on the low melting DAG fractions. Moreover, the retardation effects enhanced as the esterification degree of DGE decreases.