Synthesis,Characterization And The Application Of High Purity Lauric Acid Series Diacylglycerols

Diacylglycerols(DAG)is a product after the esterification of two hydroxyl groups on glycerol with fatty acids.DAG has a good industrial prospect and a wide range of applications in food,medical,and chemical industries,attributed to its emulsification,lubrication,and nutritional safety features.In this paper,DAGs with different carbon chain lengths were prepared through enzymatic and chemical esterification,and the effects of different purification processes on their physical and chemical properties,thermodynamic properties,crystallization properties and kinetics were studied.DAG was then used as a gelator to prepare oleogel and oleofoam,and the foaming ability of DAG and the effect of DAG on the stability of the oleofoam were systematically investigated.The main findings are as follows:(1)Enzymatic and chemical esterification techniques were used to synthesize Medium chain diacylglycerol(MCD),Medium and long chain diacylglycerol(MLCD)and Long chain diacylglycerol(LCD).The crude products obtained were then purified via three separation and purification methods:Deodorization(DO),Molecular distillation(MD)and Silica gel column chromatography(SGCC)to increase the purity of DAG.Analyzing the content of DAG by gas chromatography,it was found that the DAG content in MCD and LCD and also the product yield were higher in the enzymatically synthesized sample comparing to that of the chemical esterification.After purification,the DAG content in all the samples increased significantly.The DAG purified by SGCC had the highest purity(96–99%),followed by the samples obtained by MD purification(58–79%)and lastly,the samples obtained by DO purification(39–59%).By integrating the peaks in the ~1H–NMR spectrum,it was found that the ratio of 1,3–DAG in all samples was higher than that of 1,2–DAG.(2)To study the physical and chemical properties,thermodynamic properties,crystal polymorphism and crystallization kinetics of MCD,MLCD and LCD before and after purification by different purification methods.The crystallization kinetics of DAG was investigated by using the Avrami equation,and it was found that the Avrami constants and coefficients were different for the various DAG of different purities.The thermodynamic properties of DAG were investigated by using the differential scanning calorimeter,and it was found that the melting and crystallization temperature of purified DAGs increased compared to the corresponding crude products.The PLM and XRD results showed that the DAG microstructures and crystal form were different for the DAG of different purities.different purification methods have a modification effect on the crystal structure,and the unstable?and?'crystal forms are transformed into the stable?crystal form.(3)Preparation of soybean oil oleogel using lauric acid and its glycerides as gelling agent followed by the evaluation of the oleogel's solubility,thermodynamic properties,crystal polymorphism,microstructure,crystalline properties and rheological properties.The results show that at 22°C,the critical gel concentrations of Lauric acid(LA),Monoacylglycerol(MAG),DAG and Triacylglycerol(TAG)are:15,6,8,8 wt.%.The XRD spectra showed that all four glycerides have homogeneous polymorphism,and they all transform into a stable?crystal form after forming an oleogel.The results of contact angle analysis show that glycerides and their oleogel have good lipophilicity.DSC results show that the faster the temperature rate,the lower the crystallization temperature and the higher the melting temperature.The effect of cooling rates on the microstructures were significantly different:the crystal sizes of the oleogels prepared by LA,MAG and TAG under slow cooling were larger than that of under rapid cooling.(4)The foaming ability and foam stability of the oleogel systems preapared using lauric acid and its glycerides under different whipping temperatures(4°C and22°C)was explored,and the differences in storage stability and stabilization mechanism of different foam systems were compared.It was found that DAG showed higher foaming ability and foam stability than that of LA,MAG and TAG oleogel systems after whipping.PLM images showed the formation of interfacial crystals in LA and MAG samples while network of crystals were observed in the TAG foams.The oil foams formed by the four glycerides were all thermo–sensitive and defoaming can occur at a certain temperature.In MAG and DAG oleofoams with interfacial crystallization,interfacial crystallization occurred whereas for the TAG oleofoam,the melting of network crystallization occurred.This indicated that the foam stabilization mechanism were different for the different oleofoam systems.