Submitted to: Journal of American Chemists Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 13, 1999
Publication Date: N/A
Interpretive Summary: The accurate determination of the free fatty acids in cottonseed and cottonseed oils is a difficult problem because the method of oil extraction affects the free fatty acid content and the chemical methods used to measure the acids are not specific for only fatty acids. To increase our understanding of these issues, cottonseed free fatty acids were measured for oil samples extracted by several methods, and the measurement of the acids was conducted by chemical and chromatographic methods. The results show that the fatty acids are extracted at a slower rate than the other oil components and hence complete extraction of the oil is required for an accurate free fatty acid determination. However, good correlations were obtained between extraction methods, which facilitates the use of a quick and simple extraction process for estimating the inherent free fatty acid content. The measured free fatty acid concentrations were about 5% lower from the chromatographic determination than from the chemical approach. The results will be of interest to the cottonseed industry and to researchers studying field, harvest, and storage conditions that result in elevated seed free fatty acid concentrations.
Technical Abstract: Crude oil was extracted from cottonseed by three different methods to study the influence of extraction technique on the measurement of free fatty acids (FFAs). The methods of extraction greatly affected the concentration of FFAs in the recovered oil. Extraction processes that recovered more oil had higher levels of FFAs. In addition, the highest levels of FFAs were found in oil recovered by Soxhlet re-extraction of the defatted meal initially extracted by a less effective extraction process. The FFA concentration of oils recovered by Soxhlet extraction correlated well (R2 less then 0.98) with the FFA concentration of oils recovered by the other extraction methods. FFAs were measured by titration with sodium hydroxide and by gas chromatography of silylated derivatives. The two methods correlated well (R2 equal 0.998) with the titration method giving 5% higher values for FFAs than the chromatography method. Half of this difference was due to the oleic acid approximation used in the titration approach. The other half of the difference appears to be due to the detection of other acidic components within the crude oil.