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Procedure for QuickTox™ Kit for Aflatoxin Bulk GrainHands-on module for detecting the presence of aflatoxin in a corn sample. Food Safety Scientist Curriculum © 2014 Board of Regents, South Dakota State University iGrow.org This project was supported by the USDA NIFA grant number
Lab Safety Protocol Wear lab safety glasses, gloves (non latex)Use caution when handling methanol and/or ethanol, they are both highly flammable and toxic. Keep away from heat, sparks and flames. Lab coat and exhaust hood is also advised for those preparing solvents. © 2014 Board of Regents, South Dakota State University iGrow.org
Aflatoxin in Corn Problem/IssueCertain molds that can grow on corn may produce aflatoxins. Aflatoxins are harmful or fatal to livestock, and are considered carcinogenic to animals and humans. Agricultural producers, elevators (storage), and food processing facilities continually monitor for the presence of molds and test for the presence of food toxins. The FDA has acceptable aflatoxin levels in corn based on intended use: i.e., feed for dairy cattle – is zero © 2014 Board of Regents, South Dakota State University iGrow.org
Aspergillus mold Aspergillus on corn Microscopic picture© 2014 Board of Regents, South Dakota State University iGrow.org
How do you test for the presence of aflatoxin?Three levels of testing Black Light test (also called the Ultraviolet light test) Mold emits a greenish gold fluorescence under a black light. ELISA – immunoassay test kit Detection of specific proteins found in aflatoxin Uses antibodies to identify these proteins. Analytical Laboratories – use highly accurate tests to quantify the actual levels of aflatoxin. © 2014 Board of Regents, South Dakota State University iGrow.org
ELISA TEST – Enzyme-linked immunosorbent assayFour Steps: 1. Prepare sample 2. Extract 3. Dilute 4. Run test SUPPLIES AND EQUIPMENT per test: 1 or 2 test strips Fixed volume transfer pipette (one for each test strip) Reaction vial (one for each test strip) corn sample – ground (20 mesh) 70% methanol or 50% ethanol solution plastic (or glass) sample container with tight fitting lid. Graduated cylinder (10 or 25 ml) Tap water Timer *items can change based on source of testing kit. © 2014 Board of Regents, South Dakota State University iGrow.org
Interpret Results Negative Sample containing <20 ppb will develop 2 distinct lines in the test area (Control line and test line) Positive Sample contains > 20 ppb will develop 1 distinct line in the test area (Control line) Failed Test No lines form in the testing area. Is this a quantitative or qualitative test? Is this a quantitative or qualitative test? This is a qualitative test – it tells us yes that aflatoxin is present above 20 ppb. It does not tell us the actually level. Quantitative tests are used for these purposes: thin layer chromotography, mass spectrometery, Diagram: QuickTox Kit Product Insert. Envirologix © 2014 Board of Regents, South Dakota State University iGrow.org
Reference: This procedure was adapted from the QuickTox™ Kit for Aflatoxin Bulk Grain product insert, This procedure is specific to this test kit. This is also available at the EviroLogix™ Company website: A step-by-step visual for using the QuickTox Kit for Aflatoxin can be viewed at © 2014 Board of Regents, South Dakota State University iGrow.org
Obtaining Corn Sample Ground Corn Sample – grind using food mill, Romer mill or coffee grinder (thoroughly cleaned and disinfect with 70% ethanol) Measure out 10 grams of ground corn. Place the 10 grams ground corn into the plastic sample cup with lid. Do you think it matters how finely the corn is ground? Do you think it matters how finely the corn is ground? Yes it does. If you were doing this test for diagnostic purposes you would have all the equipment required to mill the corn to the size of a 20 mesh sieve. This ELISA kit has been developed for diagnostic purposes and it is important that good lab techniques are used so the results are reliable. If testing is not conducted with precision and accuracy, what could be the ramifications? 1) there could be a false positive and the corn would not be allowed to be used for food for humans or animal feed – this would be very costly, or there could be a lot of time and expense into further testing when it wasn’t necessary. 2) A false negative would also be very serious – corn that is contaminated with aflatoxin would get into the food supply and put animals and humans at risk for serious health problems. © 2014 Board of Regents, South Dakota State University iGrow.org
Extract aflatoxin from corn sampleSolubilizing aflatoxin, if present. Add two volumes of solvent (either 70% methanol or 50% ethanol) to the 10 grams of corn in the sample cup. Calculate the amount solvent needed _____ grams ground corn X 2 = _____ ml of solvent Cap the sample cup tightly. Shake for 1 ½ to 2 minutes. The sample will separate into two layers, the top (yellowish) layer contains aflatoxin residues, if present. Why do we use ethanol or methanol as a solvent? Photo: QuickTox Kit Product Insert. Envirologix. Why do we use ethanol or methanol as a solvent? Aflatoxins are soluble in these solutions, and many of the other components of the corn are not. So, this will remove the aflatoxin from the corn into the liquid portion of the solution if it is present. © 2014 Board of Regents, South Dakota State University iGrow.org
Dilute extract with waterTap water (small amount in a very small sample cup) Using the fixed volume pipette -150 microliters (μl), transfer tap water into the small reaction vial. Use the same fixed volume pipette, transfer 150 μl from the top (yellowish) layer of sample. Mix water and sample extract thoroughly by stirring with the tip of the fixed volume pipette © 2014 Board of Regents, South Dakota State University iGrow.org
Run the QuickTox™ Strip TestCarefully handle the strip - no bending or getting it wet WITH ARROWS POINTING INTO THE REACTION VIAL – place the strip into the reaction vial. Allow test strip to set in the reaction vial for five minutes so the sample can flow up the strip, and it can develop. How does the sample move onto the testing area of the strip? Capillary action © 2014 Board of Regents, South Dakota State University iGrow.org
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