Research On Synthesis And Properties Of Glycerol Monolaurin Derivatives

Glycerol monolaurin(GML) is not only a new, safe and efficient antibacterial agent, but also an excellent emulsifier. It has already been used in so many fields such as food, cosmetics and pharmaceuticals industries. It is so valuable to research on GML because it has advantages of relatively stable antibacterial effect, broad spectrum antibiotic and that it can be synthesized by a variety of methods and with different catalysts. However, in China most GML produced by manufactures has a low purity. Studies about GML are sporadic by scholars. Studies about Polyglycerol Monolaurin(PGML) and other Lauric acid derivatives are less. Therefore, this research systematically studied the synthesis of Lauric acid derivatives and their characteristics, hoping to get some products of Lauric acid derivatives with better application feature.Lauric acid derivatives including Glycerol Monolaurin(GML), mixture of Glycerol Dilaurin and Glycerol Trilaurin(GDL+GTL) and Polyglycerol Monolaurin(PGML) were synthesized in this research. A new solid acid salt——sodium hydrogen sulfate(Na HSO4) was used as a catalyst in the esterification reaction, and the method of synthesis in vacuum was used to replace the N2 or CO2 to protect the product from oxidation. By single factor experiment, the optimal reaction conditions were obtain as bellow: 0.3% Na HSO4 by weight of lauric acid, molar ratio 1:2 of substrates, 200℃ and 5h in vacuum. Under this condition, the original content of GML was 62.98%. After molecular distillation, the purity of GML could reach more than 90%. At the same time, content of the reactant and products and their changes during the reaction were tested by HPLC. By comparing the consumption of Lauric acid in the reaction using methods of HPLC and titration, the feasibility of using the acidity to preliminary judge the progress of the reaction was analyzedMethods of HPLC, infrared spectroscopy, mass spectrometry and 1HNMR were used to test the product and confirm their molecular structure. GML was eluted by N-hexane: isopropanol=10:1 on silica gel column, and its characteristic absorption peak occurred between 12 to 16 min. In the infrared spectrum, hydroxyl, carbonyl of the ester bond, and ether bond of PGML were tested. In mass spectrum, corresponding molecular mass peak were tested. Characteristics hydrogen were both tested in spectrum of 1HNMR of GML and PGML, which the spectrum of lauric acid didn’t have.The minimum inhibitory concentration(MIC) of Lauric acid derivatives to Staphylococcus. aureus, Bacillus subtilis, Lactobacillus, Salmonella. sp and Escherichia. coli were tested by Dull Colony Notation. The effects of different p H plate medium to antibacterial activity were compared. The results showed that lauric acid, GML and PGML all had high antibacterial activity to both gram-positive bacterium and gram-negative bacterium, but the activity of lauric acid and GML were better than PGML. GDL+GTL had no antibacterial activity. At the same time, GML and PGML had good antibacterial activity at the plates of p H=5, 7 and 9, so the p H of the plates had little effect to the antibacterial activity of the product. Method of turbidity comparison was used to test the inhibitory curves in liquid medium of GML and PGML. The result showed that Lauric acid derivatives had the best antibacterial effect at acidic p H, the second at neutral p H, and the worst at alkaline p H. However, the antibacterial activity of GML and PGML were better than sorbic acid at the same concentration in liquid medium.Foaming ability was compared between GML, PGML, Tween-20 and stearic acid glycerol monoglycerides. Their order was below: PGML≈Tween 20>stearic acid glycerol monoglycerides >GML. Through testing the conductivity, the impact of different initial oil/water ratio to emulsion type and the thickness of emulsion layer was studied when using GML and PGML as an emulsifier. It was confirmed that the optimum emulsion formatting condition was oil/water=7/3. By stability experiment, it was known when the emulsion was formed with PGML as an emulsifier, it was more stable than formed with GML. So PGML might be more suitable for being an emulsifier.The inhibition rate to the hepatocytes was tested by MTT method. The experiments showed that in a low concentration, the inhibition rate increased rapidly as the concentration of the compounds did. But after a certain value, the inhibition rate was relatively stable though the concentration rose. The inhibition to hepatocytes of lauric acid, GML and PGML were all below 50% in a high concentration. So they showed low cytotoxicity.