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United States Department of Agriculture

Agricultural Research Service

Title: Supercritical Fluid Extraction of Fat from Ground Beef: Effects of Water on Gravimetric Amd Gc-Fame Fat Determinations

Authors
item Eller, Fred
item King, Jerry

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 2, 2001
Publication Date: N/A

Interpretive Summary: Current Federal regulations require that for foods such as ground beef the total fat content of foods be reported but not the specific types of fat present. Because of this, the fat can be extracted from ground beef and then can merely be weighed and the total fat determined. However, if water is present in the fat extract, the percent fat found in the food will be too high. This research studied ways to prevent water from interfering with the accurate determination of fat in ground beef. It was found that if alcohol was added to carbon dioxide (a gas in the air we breath) to extract fat, more water was present in the extract than if carbon dioxide was used alone. We can pressurize an environmentally friendly part of air, add alcohol to it and determine fat in ground beef. Microwave drying of the fat after it was extracted from the meat gave an accurate percent fat for the food label. These results will assist food processors as well as government agencies such as the Food Safety and Inspection Service in accurately determining fat levels in their analyses of ground beef and other food products.

Technical Abstract: This study investigated the supercritical carbon dioxide (SC-CO2) extraction of fat from ground beef and the effects of several factors on the gravimetric determination of fat. The co-extraction of water was found to cause a significant overestimation of gravimetric fat. The use of ethanol modifier with the SC-CO2 was not necessary for efficient fat extraction but the ethanol did increase the co-extraction of water. Oven-drying ground beef samples prior to extraction inhibited subsequent fat extraction and oven drying after collection decreases the subsequent gas chromatographic fatty acid methyl ester (GC-FAME) fat determination as well. None of the drying agents tested were able to completely prevent the co-extraction of water, and silica gel and molecular sieves inhibited the complete extraction of fat. Measurements of collection vial mass indicated that CO2 extraction/collection causes an initial increase in mass due to the density of CO2 followed by a decrease in vial mass due to the removal of adsorbed water from the collection vial. Microwave drying of the empty collection vials removes ca. 3 mg of adsorbed water and 15-20 minutes is required to re-equilibrate to the original mass. For collection vials with collected fat, microwave drying effectively removed co-extracted water and the collection vials were essentially re-equilibrated after ca. 10-15 minutes. Silanizing collection vials did not significantly affect weight lost during microwave drying. SC-CO2 can be used to accurately determine gravimetric fat for ground beef, and this method can also be followed by a GC-FAME method to provide specific fatty acid information as well.

Last Modified: 7/28/2014
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