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Several methods of aflatoxin analysis of grain exist, each with different levels of precision, relative costs, and ease of application. These include the black light, mini-column, ELISA (serological), and chromatography techniques.
1. Black light: Grain infected with Aspergillus flavus produces a compound called kojic acid, which characteristically produces a greenish-yellow fluorescence when examined in a dark room under long-wave ultraviolet light (black light). Best results are obtained on cracked or ground kernels. The aflatoxin does not fluoresce; it is the indirectly related kojic acid that fluoresces. Thus the black light test is an indirect, presumptive test that does not directly detect aflatoxin. Black light positive samples usually contain some aflatoxin, but this method cannot quantify the aflatoxin levels and can give false positive responses. Due to these deficiencies, the black light test is not recommended for aflatoxin screening. However, if it is used and a grain sample is found positive with the black light test, it is recommended that a representative sample of this lot be tested using a more determinative test such as a commercial antibody test (ELISA) or the mini-column test.
2. Mini-column Test: The mini-column is a small tube containing silica gel and alumina (or other absorbents) through which sample extracts are washed for detection of aflatoxin. Differential migration rates through the column and UV light are used for detection. It is a rapid, relatively inexpensive, non-quantitative test that can be used at the buying point. The test often has been used to determine if the grain sample exceeds the FDA Guideline of 20 ppb aflatoxin. The mini-column test is being replaced largely by rapid antibody tests.
3. Antibody Test Kits: Recently, several commercial firms have marketed test kits based on serological tests including enzyme-linked immunosorbent assay (ELISA) and immunoaffinity chromatography techniques for detection of aflatoxin in grain samples. These test kits are self-contained and provide all the necessary instructions for analysis on-farm, at the elevator, or at the buying point. The various test kits available vary in their level of precision and limits in quantitative readings, and prospective users should inquire of the companies as to the specific characteristics of their test kits. The antibody rapid test kits are gaining popularity in use at buying points. Table 1 lists several sources of antibody aflatoxin test kits which have been tested and found to perform in a wide variety of laboratories.
4. Precision Chromatography: For more precise laboratory determination of aflatoxin analysis, several chromatography techniques are used. In order of increasing precision, these include thin-layer chromatography (TLC), gas-liquid chromatography (GLC), and high-pressure liquid chromatography (HPLC). These tests are primarily used in laboratories and are too time consuming and costly to be readily used at grain buying points. If these methods are desired, contact the Office of the Texas State Chemist at 979-845-1121.
Table 1: Commercial Firms with
Antibody Aflatoxin Testing Kits
| Manufacturer |
Product |
Editek
P.O. Box 908
1238 Anthony Rd.
Burlington, NC 27215
(Tel. 910-226-6311)
(Fax. 910-229-4471)
|
EZ-Screen
|
Intl. Diagnostic System Corp.
Suite 100
2620 S. Cleveland Ave.
St. Joseph, MI 49085
(Tel. 616-428-8400)
(Fax. 616-428-0093)
|
Several kits
|
Neogen Corporation
620 Lesher Place
Lansing, MI 48912
(Tel. 517-372-9200)
(Tel. 800-234-5333)
(Fax. 517-372-2006)
|
AgriScreen
|
VICAM
313 Pleasant St.
Watertown, MA 02172
(Tel. 617-926-7045)
(Tel. 800-338-4381)
(Fax. 617-923-8055)
|
Aflatest
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