TOTAL FATTY-ACID ANALYSIS OF VEGETABLE OIL SOAPSTOCKS BY SUPERCRITICAL-FLUID EXTRACTION REACTION/

Soapstock from vegetable oil refining operations is a value-added by-p roduct that finds further industrial use based on its fatty acid conte nt. Since the fatty acid content of soapstock can vary according to it s vegetable oil source or method of refining, determination of its tot al fatty acid (TFA) by an accurate analytical method is of key importa nce to purchasers of this refinery by-product. Traditionally, the TFA content of soapstock has been determined by the AOCS Official Method G 3-53 based on a gravimetric assay. Unfortunately, this gravimetric-bas ed assay requires considerable time and incorporates a considerable qu antity of organic solvent per assay. In this study, the authors have a pplied supercritical fluid extraction (SFE) with an enzymatic-based re action (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 sit u supported lipase in the extraction cell to form fatty acid methyl es ters (FAME). Gas chromatographic (GC) determination of the individual FAME, followed by quantitation based on the calculated sum of all the fatty acids from the CC analysis, allowed a precise determination to b e made of the soapstock's TFA content. The TFA contents of three diffe rent soapstocks determined by this method were slightly higher than th e 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 o rganic solvent use from 575 mt to under 2 mt of solvent by using SC-CO 2.