Comparison of Methods to Measure the Oil Contents in Oilseeds

Abstract

Nutritional labeling legislation relies on several methods estimating the fat content in foods by measuring the amount of acyl lipids and giving the results as the sum of all fatty acids expressed as triacylglycerides (TAG). Many of these methods have not been evaluated using soft oilseeds such as flaxseed, which is of increasing interest for use in foods. Four oilseeds (solin, flax, mustard and canola) were analyzed for oil content using exhaustive extraction with petroleum ether (FOSFA method, AOCS Am 2-93), extraction with chloroform:methanol (Bligh and Dyer, Folch, AOAC 983.23), two combinations of acid hydrolysis, Soxhlet extraction with petroleum ether (AOAC 996.06 and modified AOAC 996.06), and saponification. Determination of the acyl lipid content by gas chromatography (GC) was performed on the extracts obtained by FOSFA, saponification, and the two acid hydrolysis-extraction combinations. The Folch modification of the Bligh and Dyer method resulted in the removal of only about 80% of the oil recovered by the FOSFA method for flax and canola. This underestimation was likely due to a non-exhaustive extraction, repeating the extraction would probably have resulted in an increase in the amount of oil recovered. A modification of the acid hydrolysis method (AOAC 996.06), called extraction-hydrolysis-extraction, gave gravimetric results that were statistically similar to those of the FOSFA method. The acyl lipid contents obtained by the saponification/GC method were less than 5% lower than the results obtained by the FOSFA method, however there was more than 10% error between triplicates. Results obtained using the hydrolysis-extraction procedure followed by determination of oil content by GC could not be used due to the enormous variation observed between triplicates. This variation was due to a poor recovery of the internal standard and losses that occurred during the hydrolysis and/or extraction steps. © 2002, Japan Oil Chemists' Society. All rights reserved.