April 2001
Residue Testing
By Bruce Floyd
Contributing Editor
Chemical residues can occur in foods from different sources. Mycotoxins from natural sources — molds — are an ongoing problem. Other residues are from accidental environmental contamination or misapplication of animal drugs or pesticides.
When used correctly, FDA-approved pesticides and drugs should not cause public health or regulatory problems. Unfortunately, each year many cases of contamination occur due to improper use or application. With a HACCP (Hazard Analysis Critical Control Point) plan in place, residues of public-health importance should have been identified as part of the plan development.
Take the testing
First, define which contaminants have a chance of occurring and then find a reliable detection method. Whether a company uses third-party laboratories or performs the analysis in-house is a business decision. If the residue in question has public-health as well as economic significance, using a qualified, independent, third party laboratory may help avoid the appearance of a conflict of interest.
Sampling is the primary concern when trying to detect small quantities of a substance. Setting up a sampling program requires knowing the distribution of the substance in the target population. No matter how well-equipped the laboratory and how qualified the chemist, without a valid sampling plan — one developed around the distribution of the substance — chances of finding the substance, when present, is severely diminished.
Most of the chemicals of public-health significance are not uniformly distributed in a given population. One problem is the grouping, or compositing, of samples prior to analysis. Compositing can dilute “hot” samples to non-detectable levels, and if it does not reflect how production uses a raw material, it can hide problems. What’s more, unscrupulous suppliers can use your sampling methods against you. For example, the salting-in of product that falls outside of specification limits is still common. How often this occurs depends upon the raw materials’ source and the quality of the vendor-certification program.
Any residue of public-health significance that is likely to occur in a raw material must be addressed in the company HACCP plan. Depending upon the material and the governing agency, this can be easily determined or remain a mystery. This is an area where qualified experts are invaluable — industry associations are one source of good information.
A company that doesn’t process raw agricultural materials must determine that its suppliers have addressed possible residues and are actively minimizing the risk of passing on contaminated raw materials. When importing raw materials, do not assume that any control measures exist in the originating country.The level of oversight of the food chain in many exporting countries ranges from inconsistent to non-existent. Even countries that attempt to control food safety for their own citizens may not apply these controls to exports. Also, many U.S.-prohibited substances are still widely used in countries that produce many of the raw agricultural materials used in the United States.
Antibiotic problem
All raw milk in the United States is tested for antibiotic residues before it is unloaded at the processing plant. Many approved rapid-test methods exist for raw milk; these are listed in the Pasteurized Milk Ordinance (http://vm.cfsan.fda.gov/~ear/MI961. html). According to the directive, all positive results must be confirmed by conventional methods. For processed dairy products — liquid or dehydrated — the approved conventional method is the Bacillus Stearothermophilus Disc Assay (BSDA). This not only detects drugs, but also other inhibitory substances found in milk, including formalin or formaldehyde used at the farm in many developing countries. Many rapid methods are not approved for processed products and will not detect chemical contaminates. The BSDA test only takes four hours to run. However, it is empirical and must be run exactly as directed. Little things, like a plate diameter different from the one specified, can affect the results significantly. The Charm. B. stearothermophilus Tablet Disk Assay, Charm Sciences, Inc., Boston, can simplify positive-test-result confirmation.
The May 2000 “Food Safety and Inspection Service (FSIS) Backgrounder” states: “The FSIS oversees industry’s responsibility to ensure that meat, poultry, and egg products are safe, wholesome, free of adulterating residues, and accurately labeled. As part of FSIS regulatory oversight of industry, the Agency conducts annually the National Residue Program (NRP). This program tests meat, poultry, and egg products for unacceptable (violative) residues from pesticides, animal drugs, or potentially hazardous chemicals. Under the 1996 Hazard Analysis and Critical Control Point (HACCP) regulation, industry is responsible for preventing violative residues in its products. When residue violations are determined to be reasonably likely to occur, industry must address it in their HACCP plan. Violative levels of animal drugs and pesticides can have adverse health effects. A vigilant chemical-residue prevention program is essential in preventing illnesses and fostering the prudent use of drugs and pesticides in animals that enter the human food supply.
“Residue violations are followed-up in multiple ways. When violative residues are detected in food-producing animals, by any component of the NRP, FSIS currently notifies the producer whose animals are then subject to repeated follow-up enforcement testing when presented for slaughter until compliance is demonstrated. Slaughter plants are notified of violations so that plants better prevent them in their HACCP plans. FSIS also shares violations with the Food and Drug Administration (FDA) officials who conduct investigations as part of their regulatory responsibility under the Food, Drug and Cosmetic Act.” A summary of the 2000 survey can be found at www.fsis. usda.gov/OPHS/nrp2000/index.htm.
To help industry identify problem livestock producers, the names of repeat violators will be published in the future on the FSIS website along with the specific violation.
U.S. feed-industry regulation has created problems. USDA regulates the animals and FDA regulates the feed industry and the veterinarians. (For milk production, this all is within the jurisdiction of FDA.) Drug residues can come from direct treatment or through medicated feed. Medicated feed has been fed illegally to animals due to errors at the feed manufacturer.
A validated method to test for the drug must be submitted along with the new drug application; the official methods for analyzing drug residues are approved when a drug is approved for use. Although the FSIS uses many rapid-screening methods in the NRP, according to Karen Huelbak, Sc.D., chief scientist, USDA/FSIS requires that a firm use USDA, AOAC or NADA (New Animal Drug Application) methods when testing for drug residues. A firm must contact FSIS when evaluating rapid methods to determine when they can be used and which ones are approved.
Sounding out heavy metals
Atomic absorption spectrophotometry (AA) is the technique generally used to analyze heavy metals. Several different methodologies are typically specified for the metal and matrix in question and can be found in the AOAC manual and on the different government agency websites.
Many commercial testing labs have AA equipment. Again, whether or not to test depends upon the likelihood that a problem will occur at the plant. This requires staying current with potential problems that may arise due to environmental contamination, accidental spills or natural disasters in the production area of the raw materials. Under the seafood HACCP website, the FDA lists specific substances that may crop up in different species of seafood. Remember: with heavy metals, if you are not looking for the right one, you will not find it.
The problem with mold
According to Bruce Malone, vice president technical services, Trilogy Analytical Laboratory, Washington, MO, there are three mycotoxins of public-health significance: aflatoxin, deoxynivalenol (DON or vomitoxin) and fumonisin. These toxins are most often associated with grains, soybeans and peanuts, but can occur in other materials susceptible to fungal growth. Aflatoxin and fumonisin are considered to be potent carcinogens. The FDA has not established safe tolerance levels for any of the mycotoxins, but has set practical limits for aflatoxin in food and feeds. The action level is 20 ppb in susceptible commodities, and in whole milk, skim milk and lowfat milk the level is 0.5 ppb. In certain situations, even lower levels may be subject to recall.
A black-light screening test is typically used to indicate possible aflatoxin contamination of grains; however, this method can pick up false negatives and the level of aflatoxin needs to be relatively high for it to show up. Laboratory analyses must be used to confirm the presence and level of contamination.
Mycotoxin testing offers an array of analytical methods. For example, for agricultural commodities, rapid Enzyme Linked Immunosorbant Assay (ELISA) test kits can be used. The USDA Grain Inspection, Packers and Stockyard Administration (GIPSA) has a list of approved test kits. A word of caution: these test kits are to be used for the commodity listed and their use on complex matrices or processed foods is questionable. The test-kit package will indicate the products for which they are approved and the accuracy of each one when used as directed.
Products that do not lend themselves to rapid methods should be analyzed by conventional methods. It is possible to equip a lab to analyze for aflatoxin or the other mycotoxins of public-health concern, but the cost can be quite high as can the cost of a qualified chemist to perform the analyses. For a large, continuing number of samples, the solution would be to equip one’s own lab. One source of laboratory equipment is LabAlliance, State College, PA, which sells HPLC Post-Column Derivatization (PCD) systems for the analysis of aflatoxins.
Alternatively, an outside testing lab may be used. USDA/GIPSA offers analytical services as well as sampling programs. Another lab that offers mycotoxin-testing services is Trilogy Analytical Laboratories (TAL), Washington, MO, which will help a company set up a mycotoxin-sampling program and also serve as a reference lab. TAL produces and sells primary aflatoxin standards to other laboratories.
Due to the nature of mycotoxins, the sampling plan and sample preparation are as important as the analysis itself. An additional problem is the tendency of test kits to give false positive readings. It is not permissible to resample the lot in question. It is necessary to have a sample preparation protocol that shows that another portion of the original ground sample will have the same probability of containing the residue in question at the same levels. This is not easy. Seek advice from someone qualified to develop sample plans and review laboratory protocol. No one wants to have a regulatory agency discover a violative level of a residue in a product on the market and then have to defend its release to the consuming public based on a re-test.
Pesticide problems
According to David Elliott, Ph.D., president, Environmental Micro Analysis, Inc. (E.M.A.), Woodland, CA (www.emalab.com), the sophistication now required to do pesticide testing along with the expense of equipping and staffing a lab and the seasonal nature of the testing can be prohibitively expensive to any one company. E.M.A. offers extensive testing of pesticide residues and performs multiple screens as well as individual analysis. The company also has a program to analyze FDA-detention samples with complete documentation. Two other laboratories performing pesticide testing are Medallion Labs, Golden Valley, MN and TPC Laboratories, Minneapolis.
Again sampling is a major issue. Some groups will set up a sampling program and arrange for the analysis, such as Scientific Certification Systems (SCS), Oakland, CA. According to Eric Engbeck, director, agriculture program, the key to sampling is knowing the type of pesticides being used and how they are being applied. Its “NutriClean” program — offered to growers and retailers — will certify that raw agricultural products have no detectable pesticide residues. The SCS standard is less than 0.05 ppm., which is at or below the U.S. tolerance limits. One caution with pesticide sampling, according to Engbeck, is that field crop results do not necessarily represent the final residue level in a given crop; washing, peeling and cooking can reduce the levels of some pesticides.
Meat speciation
With the growing concern over Bovine Spongiform Encephalopathy (BSE), some manufacturers who import raw meat, meat byproducts or feed concentrates might want to know if they contain any beef. It is possible to detect beef — raw and cooked — down to 1% using ELISA Technologies, Inc, Gainesville, FL test kits. The company offers two USDA/FSIS-approved tests: DTEK™ Immunosticks Test Kits, for raw meat and ELISA-TEK™, for cooked meat. The ELISA-TEK™ Cooked Meat Kit is especially useful for detecting dried blood and rendered meat protein in feed concentrates. These will not determine the specific tissue type, but will detect if any part of a particular specie is present. Test kits exist for cooked beef, pork, sheep, horse and deer, and for raw beef, pork, poultry, sheep, goat, horse, rabbit, kangaroo and water buffalo.
Companies that have HACCP plans must review them to make sure they have considered the possibility that residue contamination will occur. Of course, if one does not have a HACCP plan, now is a good time to start. Knowledge of the raw materials being used and the quality of the supplier is basic to a residue-testing program. The sampling plan developed and the analytical methods used depend on knowledge of the raw material. This knowledge will lead one to design an adequate sampling program and select analytical methods suitable to the material being tested.
Bruce Floyd established Process Systems Consulting, Iowa City, IA, after working more than 30 years in the food processing industry. He has had extensive experience in sanitation, quality control, regulatory relations, and product and process development (both domestic and international), and specializes in integrating ingredient and manufacturing specifications into total process systems. A graduate of Georgia State University, he has successfully completed all areas of the Better Process Control School at the University of Minnesota, and has been qualified by the International HACCP Alliance as an instructor. He can be reached via e-mail at [email protected].
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