TOTAL FATTY ACID ANALYSIS OF VEGETABLE OIL SOAPSTOCKS BY SUPERCRITICAL FLUID EXTRACTION/REACTION (SFE/SFR)

Authors: KING, JERRY; TAYLOR, SCOTT; Snyder, Janet; Holliday, Russell

Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/3/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Soapstock is a by-product of the vegetable oil industry that has commercial value due to the presence of fatty acids in its composition. These fatty acids are chemicals that can be purified or reacted to make other useful chemical derivatives. Soapstock can also be used as a feed additive and fertilizer. Regardless of its end use, soapstock is purchased based on its sfatty acid content, therefore, a rapid analysis method must be employed to certify its chemical content. Current methodology involves a labor intensive, time consuming technique that also uses considerable solvent to complete the assay. In this study, we have developed an alternative technique that takes advantage of the solvent properties of compressed gases, namely carbon dioxide, to simultaneously extract and react the fatty acid components from the feedstock prior to chemical analysis. The technique utilizes less than 2 milliliters of solvent compared to 575 ml of solvent used in the conventional method. In addition, the new method takes approximately one half the time of the older solvent intensive method. The results obtained from the new method are more precise than those from the traditional method and provide more information about the chemical components present in various lots of soapstock. With these advantages, the newly developed method should aid industrial purchasers of raw soapstock in assessing the quality of shipments they are receiving and also avoid detention charges on tanker trucks delivering the product to a plant site.

Technical Abstract: Soapstock from vegetable oil refining operations is a value added by- product which 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, we have applied supercritical fluid extraction (SFE) with an enzymatic based reaction (SFR), in the presence of supercritical carbon dioxide (SCCO2), 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 FAMES, 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 content 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 half the time of Official Method G3-53 and reduces organic solvent use from 575 ml to under 2 ml of solvent by using SCCO2.