Oil Content Analysis: Myths and Reality

Abstract

The FOSFA (Federation of Oils, Seeds and Fats Associations Limited) extraction method (harmonized as AOCS Am 2-93 or ISO 659) is considered to be the reference method to measure the oil content of oilseeds. The method is based on the extraction of neutral lipids with hexane or petroleum ether, and the extracted components are estimated gravimetrically and defined as crude fat or oil content. The method requires a triplicate grind/extraction, making it lengthy and very detailed for the analyst. Compared with other official methods (AOAC 996.06), the FOSFA extraction method gave the highest oil recoveries in all oilseeds tested. Accelerating the extraction through the use of new instrumentation, which combines solvent extraction with a physical disruption such as pressure or microwave heating, has not been able to give oil recovery equal to the FOSFA extraction. Although the FOSFA method remains the reference method, both ISO and AOCS have identified a need to develop new rapid methods for oil extraction that yield oil equivalent to that from the FOSFA method and that can be used for determination of other factors such as methyl esters or free fatty acids. This study examined the lipid components extracted by each stage of the FOSFA method: First Extraction (FOSFA1), Second Extraction (FOSFA2), and Third Extraction (FOSFA3). In a typical analysis, FOSFA1 accounted for ~86%, FOSFA2 for ~13.5%, and FOSFA3 for as much as 0.5% of the total oil extracted. Although mainly triacylglycerols (TAG) were found, the extracts contained small amounts of other lipid components including nonesterified fatty acids, partial glycerides, fat-soluble vitamins, long-chain alcohols or aldehydes, and sterol or cholesterol esters. More nonpolar material was extracted in the first early stage of the extraction, whereas the later stages contained more polar material. The oil in FOSFA1 and FOSFA2 contained close to 98% TAG based on methyl ester determination. The analyses of the phosphorus content by graphite furnace atomic absorption spectrophotometry showed that almost no phosphorus (below limit of detection) was found in FOSFA1 and FOSFA2 oils but small amounts of phosphorus were present in FOSFA3 oils. This indicates that only ~0.5% of phospholipids were present in the FOSFA3 oils, suggesting that only very small amounts (<0.005%) of phospholipids are extracted by the total method when the three extracts are comCopyright © 2004 AOCS Press bined. Moreover, during the extractions of canola by the FOSFA method, the proportion of triacylglycerol (TAG) with n-7 fatty acids increased with each step of the process. These fatty acids are associated with the seed coat in canola seeds, and the increase suggests that these structural lipids are the last lipids to be extracted.