After sampling, the next phase of mycotoxin detection involves extraction of the toxin from the food matrix. Officially recognized extraction methods for foods are prescribed by the AOAC INTERNATIONAL Official Methods of Analysis (32) and for feeds by the International Standards of Organization (ISO) publication or the European Economic Community (EEC) directives (5,33-35). The main purposes of extraction are to transfer toxin from the sample to a solvent and to remove unwanted contaminants and interferences (2). The efficiency of extraction of mycotoxins depends on the physiochemical properties of the food matrix as well as those of the toxin.

Mycotoxins are often extracted from food or agricultural products by blending or shaking the sample with appropriate amounts of solvent (6). High-speed blending has the advantage of reducing the sample particle size, which may lead to better extraction (5). The selection of solvent type and ratio of sample to solvent volume depends on the mycotoxin of interest and the source material. The solvent-to-sample ratio is usually 2-5 mL:l g sample. Most mycotoxins are readily soluble in organic solvents but sparingly soluble in water (5). Typical extraction solvents include chloroform, ethyl acetate, methanol, acetone, acetonitrile, and mixtures of these organic solvents and water. The water wets the substrate and increases penetration of the solvent mixture into the hydrophilic matrix (16). The aqueous phase can be acidified to release the toxin from interactions with proteins in the food. Sodium chloride or other inorganic salts are often added to the aqueous phase to reduce emulsion formation. In addition to liquid solvents, supercritical fluids (eg, C02 with methanol or acetonitrile as modifiers) have been successfully used to extract aflatoxin (36) and trichothecenes (37,38) from grain and feed. Nonpolar solvents such as hexane or 2,2,4-trimethylpentane can be used to defat samples of high-lipid content before extraction.

After extraction, filtration is often necessary to remove unwanted solids. When using highly nonpolar solvents, a common practice is to add a diatomaceous earth filter aid to assist in filtration. Centrifuging extracts prior to cleanup is a common practice when filtration difficulties arise (5).

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