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Cutting use of laboratory solvents.

Supercritical fluid extraction may never be a household word, but federal researchers are hearing good things about it.

This process, known by the acronym SFE, provides a cost-effective way to help obtain information on trace levels of toxicants in foods without the use of chemical solvents. It may be important in helping federal regulatory agencies comply with U.S. Environmental Protection Agency (EPA) rules.

Recently, as part of a pollution-prevention strategy, EPA mandated that all federal agencies cut back on solvents used in laboratory procedures. It has called for a 50-percent reduction in the use of 17 target chemicals in all federally owned and contract-oroperated laboratories by 1995. All other federal facilities must reduce by one-third the use of these chemicals by 1995.

ARS' NCAUR (National Center for Agricultural Utilization Research) in Peoria has become a leader in SFE technology. Companies from all over the world have visited the center to learn about the process.

NCAUR chemist Jerry W. King has enabled many federal agencies to gain access to SFE, including USDA's Food Safety and Inspection Service (FSIS) and Federal Grain Inspection Service (FGIS), and the Food and Drug Administration FDA).

SFE isn't new. Food processors have been using it to decaffeinate coffee, extract hops for flavoring beer, and perform other food-processing tasks.

The SFE technique uses gases, such as carbon dioxide ([CO.sub.2]) or nitrous oxide, heated and compressed to high densities to the point that they resemble liquids. Carbon dioxide has been the gas preferred by most researchers engaged in supercritical extraction, says King.

SFE uses [CO.sub.2] kept at an intermediate state between gas and liquid, at selected pressures and temperatures, to extract target substances from food samples - with no harmful effects to the food.

And NCAUR researchers have proven that SFE can be used to replace specific steps in the soybean oil refining process, thus eliminating the need for processing chemicals that the industry finds difficult to dispose of.

King and co-researchers at the Peoria center have adapted and refined equipment to make SFE safer and less expensive than standard tests for monitoring pesticide residues in fatty foods, like meats, and in nonfat foods, such as produce.

"In low-fat foods, the use of chemical solvents hasn't been very effective," says Richard Ellis, Director of the FSIS Chemistry Division in Washington, D.C. FSIS is responsible for checking fresh and processed meat and poultry products to ensure that they are safe and wholesome.

Although the United States has banned the use of DDT, for example, other countries may not have restricted the use of chlorinated pesticides, which don't easily degrade and may persist in the environment.

In several collaborative studies with other agencies, King has used SFE to analyze the pesticide content of a variety of foods. With FDA and FGIS, he bas examined nonfat foods such as carrots, wheat, lettuce, and spinach. For FSIS, he has extracted fat from meat products, such as frankfurters and hamburger. The fat-removal process is important in meats because pesticides tend to concentrate in the fatty tissue.

Based on these tests, King says SFE yields accurate analyses comparable to those obtained by standard analytical methods using chemical solvents.

Several other factors make SFE worth considering as an alternative to standard analytical methods currently used by these regulatory agencies. It's safer for laboratory workers, and [CO.sub.2] won't harm the environment.

SFE is also potentially less expensive than standard analytical methods that rely on chemical solvents to extract pesticides and drugs from food products.

Marvin Hopper of FDA's Total Diet Research Center in Kansas City, Missouri, says, SFE reduces the cost of both purchasing chemical solvents and disposing of them. It costs about $3 per sample to analyze nonfatty foods, such as vegetables, with chemical solvents. SFE can do the job for 75 cents per sample.

"The cost of analyzing a fatty food with chemical solvents is about $1.50 - double an SFE - processed sample," adds Hopper.

It also saves time. Chemical extractions using ether or hexane as solvents can take from 3 to 5 hours. With SFE, lab technicians obtain similar results in about 60 minutes.

ARS engineeling technician Jim Johnson has built a multisample instrument that can process six samples simultaneously. His version is based on earlier units developed by King and Hopper.

Johnson installed the six-sample unit at the FSIS laboratory in Alameda, California, in September 1992 and showed FSIS personnel how to prepare samples and operate the unit.

An SFE device is also used in FDA's Total Diet Study, which is regarded as a reference in setting regulatory tolerances and in monitoring pesticides in the food supply. The FDA laboratory in Kansas City periodically measures levels of pesticide residues in 234 common table-ready foods.

"In the future, SFE may also be able to provide further detailed analytical studies on food samples. That would be helpful in determining the precise nutritional composition of foods, to comply with new FDA food-labeling requirements," says King.

King's original multisample SFE unit was studied and improved on in 1989 by Lee Scientific, a division of Dionex Corporation, located in Salt Lake City, Utah. The firm has since marketed a miniaturized model.

Meanwhile, FSIS plans to use an SFE multisampler to check low-fat imported meat products for pesticides.

Ellis of FSIS' chemistry division says, "We've targeted for elimination five chemicals - chloroform, dichloromethane, mercury, toluene, and xylene - that we routinely use in our laboratories for food composition, residue analysis, and the study of diseased tissue."

He says that FDA tolerances for many chlorinated hydrocarbon pesticides are between 100 to 300 parts per billion. Analytical methods used by FSIS now detect residues as low as 10 to 20 parts per billion.

Although FSIS currently recycles solvents to reduce the cost of purchasing new reagents, they hope to convert to supercritical fluid extraction to help alleviate the impact of their current testing protocols on the environment.
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Author:Cooke, Linda
Publication:Agricultural Research
Date:Mar 1, 1993
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