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United States Department of Agriculture

Agricultural Research Service

Title: Supercritical Co2 Extraction of Fat: a Comparison of Gravimetric and Gc-Fame Methods

Authors
item Eller, Fred
item King, Jerry

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 8, 1998
Publication Date: N/A

Interpretive Summary: The determination of the fat content of various food and agricultural products has become increasingly important to the health conscious consumer in recent years. Traditionally, the fat content of foods was determined by extracting fat using a liquid solvent. Recent concerns about the use of solvents in the laboratory have required chemists to consider alternative methods for extracting fat from food. A technique utilizing predominately high pressure carbon dioxide was very effective in removing fat from the food. However, extraction with either liquid solvents or high pressure carbon dioxide can remove non-fat components from food, and the weight of the extracted may be incorrect compared to the true fat content of the food. Application of an analytical method that specifically identifies the components contributing to the total fat content of the food has proven more accurate. This method is important to regulatory agencies, such as the Food Safety and Inspection Service, and provides the American consumer with more accurate information about the fat content of the foods they consume.

Technical Abstract: Direct comparison of gravimetric and gas chromatographic (GC) fatty acid methyl ester (FAME) fat based determinations of supercritical fluid extracts (SFE) was made for several food matrices. Five oilseeds (soybean, sunflower, canola, safflower, and cottonseed), three ground beef samples (ca. 10, 20, and 30% fat), five bakery samples (bread with emulsifier, cake with emulsifier, cake with shortening, cookies with emulsifier/shortening, and crackers with shortening), and NIST Standard Reference Material 1544 (SRM-1544) were extracted with supercritical CO2 and ethanol. The collected material was weighed and total fat determined gravimetrically (SFE-GRAV). Subsequently, an internal standard was added to the extract, the material converted to FAMEs and analyzed by GC to determine total fat (SFE-GC-FAME). With the exception of the oilseeds, these matrices were also digested using acid hydrolysis, the fat extracted with ether/hexane, transesterified and analyzed by GC to determine total fat (AH-GC-FAME). For sunflower and cottonseed, the SFE-GRAV results were higher than the SFE-GC-FAME results, whereas the two methods gave equivalent results for soybeans, canola, and safflower. For the ground beef samples and SRM-1544, the SFE-GRAV results were significantly higher than both GC-FAME results (i.e, SFE and AH), whereas the latter methods were equivalent. For the high-fat bakery samples containing shortening, the SFE-GRAV, and GC-FAME results (i.e, SFE and AH) were in good agreement. For the emulsified low-fat bakery products, however, the SFE-GRAV results were higher than the SFE-GC-FAME results.

Last Modified: 4/24/2014
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