Which types of esters can be formed? How are methyl esters produced and collected? Does the quantitative profile of fatty acids remain the same after converting into methyl esters??
Hello Deepshikha
You can convert fatty acids in seed extract by esterification & trans esterification reaction using methanol. With this you will get methyl ester of fatty acids which can be after dilution with suitable solvent directly injected to GC-MS. The fatty acid profile will remain same after esterification.
Best Wishes
Shripad Joshi
study the website http://lipidlibrary.aocs.org/topics/ester_93/index.htm
it is absolutely useful.
Conversion of fatty acids present in the oil extracted from seeds, into their methyl esters, is the basis of bio-diesel production. Methyl esters are made from the oils by transesterification with methanol and, in general, a strong alkali like NaOH/KOH /Ba(OH)2/etc. is used as a catalyst.
Whether the fatty acid profile will remain the same after transesterification process, will depend on the kinetics of the reaction with individual fatty acids, to be exact. As these acids are normally long-chain fatty acids, differing mainly in their chain-lengths, the reaction kinetics are expected to be comparable. Some of these fatty acids also contain unsaturation. Assuming that you are achieving complete/quantitative conversion of all acids present in the oil into the corresponding methyl esters, then the quantification of these esters will give you the original fatty acid profile,as it was in the oil.
For maximum recovery, you should probably begin with alkaline hydrolysis to break down the seed matrix and release the fatty acids from complex lipids. Acidification then permits near quantitative partitioning of the protonated fatty acids into petroleum ether or like solvent (3 extractions). Evaporate to dryness and use one of several commercially available reagents to prepare methyl esters (e.g., sodium methoxide or methanolic HCl).
Derivatization of fatty acids is a complex and one of the more fascinating topics in lipids chemistry. There are two reactions:
A. Transesterification: Your fatty acids are already esterified (e.g to glycerol in triacylglycerides) and then you change that alcohol by a smaller one. It is usually methanol. As catalyst you will use a base as sodium hydroxide or sodium methoxide. But be careful an excessive reaction time will release your fatty acids as free fatty acids. So your results will be inaccurate.
2. Esterification: Your fatty acids are in free form so you want to esterfied them to an alcohol, again methanol. You catalyze the reaction using sulfuric acid/mehtanol, hydrochloric methanol, boron trifluoride. But again the problem is that although this reaction can be carried out at room temperature some alterations can happens so you need to add a solvent to avoid alterations.
I suggest you the attached works.
Article A high-performance direct transmethylation method for total ...
Check this paper
Article Analytical Characterization of Fatty Acids Composition of Da...
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