Total fatty acid analysis of vegetable oil soapstocks by supercritical fluid extraction/reaction

Abstract

AbstractSoapstock from vegetable oil refining operations is a value‐added by‐product that finds further industrial use based on its fatty acid content. Since the fatty acid content of soapstock can vary according to its vegetable oil source or method of refining, determination of its total fatty acid (TFA) by an accurate analytical method is of key importance to purchasers of this refinery by‐product. Traditionally, the TFA content of soapstock has been determined by the AOCS Official Method G3‐53 based on a gravimetric assay. Unfortunately, this gravimetric‐based assay requires considerable time and incorporates a considerable quantity of organic solvent per assay. In this study, the authors have applied supercritical fluid extraction (SFE) with an enzymatic‐based reaction (SFR), in the presence of supercritical carbon dioxide (SC‐CO2), to determine the TFA content of soapstocks. The SFE/SFR sequence was conducted using two commercially available extractors using an in situ supported lipase in the extraction cell to form fatty acid methyl esters (FAME). Gas chromatographic (GC) determination of the individual FAME, followed by quantitation based on the calculated sum of all the fatty acids from the GC analysis, allowed a precise determination to be made of the soapstock’s TFA content. The TFA contents of three different soapstocks determined by this method were slightly higher than the values derived from Official Method G3‐53. The reported method takes less than one‐half of the time of Official Method G3‐53 and reduces organic solvent use from 575 mL to under 2 mL of solvent by using SC‐CO2.