This method provides a procedure for the determination of the composition of fatty acids which are esterified at the sn-2 position (ß (beta) or internal position) of the triacylglycerol molecules in animal and vegetable fats and oils. The method is comprised of the 1(3)-position selective...
This method provides a procedure for the determination of the composition of fatty acids which are esterified at the sn-2 position (ß (beta) or internal position) of the triacylglycerol molecules in animal and vegetable fats and oils. The method is comprised of the 1(3)-position selective transesterification of the triacylglycerols with ethanol by Candida antarctica lipase to yield 2-monoacylglycerols, followed by the separation of the 2-monoacylglycerols by silica-gel chromatography, and determination of their fatty acid composition by gas chromatography. This JOCS/AOCS Joint Method was adopted from the Japan Oil Chemists’ Society “JOCS Standard Methods for the Analysis of Fats, Oils and Related Materials (JOCS eds.)” and is adapted from JOCS Standard Method 2.4.5-2016, Fatty Acid Composition at sn-2 Position of Triacylglycerols (Enzymatic Transesterification Method) and JOCS Methods for Reference, S 22.214.171.124-2016 Fatty Acid Composition of Triacylglycerols with Short Chain Fatty Acids (Capillary Gas Chromatography).
The method is applicable to fats and oils containing C4-C22 saturated and unsaturated fatty acids with a melting point below 50 °C, but not those containing hydroxy fatty acids such as ricinoleic acid. This method is applicable to oils containing polyunsaturated and short chain fatty acids, as it uses a Candida antarctica lipase that catalyzes reactions with these fatty acids to an extent similar to catalysis with triglycerides containing common saturated and unsaturated fatty acids. This lipase replaces lipases from porcine pancreas or Rhizopus oryzae (delemar), which are more limited in scope because these lipases do not react dependably with short chain fatty acids and polyunsaturated fatty acids. The transesterification reaction of triacylglycerols with ethanol by immobilized Candida antarctica lipase (fraction B) becomes more selective to the sn-1(3) position of triacylglycerols as the amount of ethanol used in the transesterification reaction is increased. 2-Monoacylglycerols and fatty acid ethyl esters from the sn-1(3) position of triacylglycerols are preferentially produced in the presence of 10 parts of ethanol by weight per part of oil. The composition of fatty acids located at the sn-2 position of the test oils is determined by isolating the 2-monoacylglycerols by silica gel chromatography, followed by their transesterification and analysis by gas chromatography.