Reinforcing the Links
in the Food Safety Chain
March 1996 -- Food Safety

By: Scott Hegenbart
Editor*

*April 1991-July 1996

  When the safety of food is compromised, the effects -- in addition to the potential loss of human life -- can be staggering. In 1992 alone, the medical costs and productivity losses due to foodborne pathogens were estimated to be somewhere between $5 billion and $6 billion ("Food Safety Issues: Modernizing Meat Inspection," Agricultural Outlook, 197, 1993).  In 1989, the Council for Agricultural Science and Technology (CAST), Ames, IA, created a task force to determine the state of knowledge about U.S. foodborne disease risks. The task force's findings were released in a 1994 report entitled, "Foodborne Pathogens: Risks and Consequences."  Among the report findings are that the "Application of hazard analysis critical control point (HACCP) systems can reduce the likelihood of foodborne illness." The report further states that "pathogens and their toxins can enter the food chain at any point from the farm to the kitchen."  By designing hurdles along the entire length of this chain, the reduction of incidence and prevention of contamination, etc. would contribute to the overall safety.  This series of articles has been developed to demonstrate how food safety is affected at various points along the entire food production chain and to offer examples of how it is/might be controlled. Although proper testing and monitoring certainly would be an important part of such a comprehensive HACCP plan, the emphasis has been given to identifying ways to reduce the incidence of potential hazards.  The 1993 outbreak of E. coli 0157:H7 in ground beef brought widespread public attention to food safety issues and served as a catalyst for proposed changes in the way the United States Dept. of Agriculture's Food Safety and Inspection Service makes certain that meat, poultry and egg products are safe. The proposed program, referred to as the "Mega Regs," includes provisions for mandatory HACCP programs to ensure safe processing of meat and poultry.  The USDA recognizes, however, that critical points affecting food safety occur before and after the processing plant and has suggested as a future goal a federal food safety system that regulates the entire food production and distribution chain. This article explores food safety issues that relate to the first links in this chain.  "It'd be nice to have HACCP on the farm, but no one knows what to do," says Steve Taylor, Ph.D., head of the department of food science and technology, University of Nebraska, Lincoln. "To put it into practice is going to take more research."  We do know that the safety of a food may be compromised by the presence of any one or a combination of microorganisms, toxins, carcinogens, etc. In many cases, the presence of these substances is inherent from the time the food is produced on the farm or harvested from the sea.  Bacteria are usually the first targets of any food safety discussion because they're behind 90% of all food safety outbreaks ("Foodborne Disease Outbreaks, Five-Year Summary, 1983-1987," Journal of Food Protection, 53, 1990). Specifically, the most common culprits are pathogenic bacteria, which are found in many places on a farm. Salmonella and E. Coli 0157:H7, for example, are found in the intestinal tracts of animals. Listeria monocytogenes and Clostridium botulinum are present in animals and are widely found in soil. Consequently, microorganisms can be found not only on meat and poultry, but on fruits and vegetables, too.  This ubiquitous nature of microorganisms in animals and soil presents a challenge for safety control in the early stages of the food chain. Nevertheless, while producing a sterile food is impractical, the farm still may serve as a control point for bacteria.  Dairy farming is one example. Here, the sanitation of the milking facility, cleaning of the cows' udders prior to milking, and careful thermostatic control of milk holding tanks are among the contributors to microbial control.  Keeping Salmonella in check in poultry involves controls such as more frequent changing of the bedding materials in holding pens. Such steps are considered by sources in the U.S. poultry industry not to be cost effective. In fact, while obviously sick animals are destroyed in the United States, eliminating Salmonella would require entire flocks to be eradicated because the incidence is so high and many animals that carry the organism are not actually ill; the bacteria is among the indigenous intestinal flora.  Europe -- Sweden, in particular has a more comprehensive program for eliminating Salmonella in poultry. There, feed is tested for the organism to avoid introducing it to the animals, and the antibodies in birds are monitored to see if the birds are infected. Although none of this sort of testing is done in the United States, we must remember that the European poultry business is much smaller, making it more practical to put such measures into practice.  A possibility that may be more practical for application in the United States is "competitive exclusion." This technique starts by isolating beneficial bacteria present indigenously in birds. These are then fed to day-old chicks before they develop their own intestinal flora. Once these beneficial bacteria become established, they can greatly reduce (but not eliminate) the incidence of Salmonella and even Campylobacter jejuni. The technique also is being studied for application in other animals.  Due to the severity of E. coli 0157:H7 infection and its extremely low toxicity level, any reduction along the food chain -- including control on the farm -- may be desirable. In addition to causing such a severe illness, 0157:H7 has been found to be much more prevalent than previously thought. Early data showed that 0157:H7 had a very low incidence rate -- about 0.2% to 0.5% of the bovine population. New data reveal this rate to be as high as 5%, according to Michael Doyle, Ph.D., professor and department head, department of food science and technology, center for food safety and quality enhancement, University of Georgia, Griffin.  At present, research into pre-harvest infections to control 0157 is still preliminary. Early results suggest that measures may be taken to reduce its incidence. These might include how the animals are fed and housed. One researcher is even examining how standing water in open troughs might contribute.  "The research on housing and feed are, at best, preliminary, and the statistical association has not always been able to be made," says Doyle. "I think there are possibilities in terms of competitive exclusion and vaccines that might be able to reduce carriage, but these aren't going to be immediate answers."  Toxins and carcinogens. All foods are combinations of various chemical components. In fruits and vegetables, these components include toxic substances that serve, in many cases, as natural pesticides. For the most part, natural toxins are consumed at levels low enough to prevent human illness -- unless abnormal amounts of a single food are consumed. In some cases, though, growth conditions can affect the incidence of toxins.  Potatoes and tomatoes, for example, contain toxic alkaloids. In potatoes, solanine appears in levels ranging from 1 to 5 mg per 100 grams of potato. The greenish potatoes that result from "sunburn" have solanine levels as high as 35 mg per 100 grams. Such levels may cause illness, and FDA regulations specify that potatoes are unfit for human consumption at 20 mg per 100 grams.  Fortunately, many natural toxins are destroyed or inactivated by processing and cooking. But consumers are eating more fresh vegetables raw. Can they be better protected? One way farmers help control solanine in potatoes is by keeping them out of the sun as much as possible once they are dug up. They do this by covering open transport vehicles with burlap and/or packing the potatoes in brown, light-blocking bags.  Scientists also have bred varieties of potato that have naturally lower solanine levels. While this approach has worked well for potatoes, it must be applied carefully. For example, the natural toxins in a vegetable may serve as natural pesticides, so reducing the levels would reduce the plant's natural defenses.  The presence of stress -- in the form of weeds, bacteria insects and so on -- can cause a plant to produce higher levels of toxin to fight the stress. Eliminating the stress through the use of herbicides, pesticides, etc., can help reduce the natural toxins a plant produces. Controlling weeds also is critical because they may contain toxins and they could be harvested along with the crop. In the Pacific Northwest, for example, nightshade in field peas is a concern because the fruit of both plants are about the same size and are a challenge to separate.  "Most of the more potent toxicants occur in weeds," says Taylor. "Controlling weeds and iminating them from fields is pretty important on this basis."  In addition to toxins, the natural makeup of foods includes a certain number of carcinogens. Anti-carcinogens also are common food components. Many sources indicate that a varied diet allows the naturally occurring carcinogens and anti-carcinogens to "cancel out" each other. Were this not the case, controlling the levels of naturally occurring carcinogens would be similar to controlling natural toxin levels.  From a consumer perspective, concern over natural carcinogens doesn't hold a candle to the concern over added carcinogens. In the early food-chain links, this refers specifically to pesticide residues. Because the type of pesticide and how it's applied directly affect residue levels, the government regulates which pesticides may be used for specific applications and sets maximum tolerance levels for residues.  The issue of tolerance levels was challenged in 1989 when the state of California and the Natural Resources Defense Council filed suit to have the Environmental Protection Agency strictly enforce the zero-tolerance restrictions of the Delaney Clause and ban certain applications for 36 pesticides. When the dust settled, the EPA agreed in a settlement to revoke both raw and processed tolerances for most of the pesticides in question.  Congress has been working to replace Delaney with a negligible risk standard defined in the Food Quality Protection Act of 1995. The reason for this is that residue testing has become much more sensitive since Delaney was written. In some cases, the levels of naturally occurring carcinogens may be higher than the carcinogenic residues of certain pesticides. As this article goes to press, the Act is still on the table. If and when it passes, it will legitimize the existing government practice of setting tolerance levels for residues.  Mycotoxins are often overlooked as a threat to the safety of food. They are produced by certain types of mold (not all types) and can occur in many types of food that are susceptible to growth of the fungi in question, particularly grains and nuts. Mycotoxins cause a variety of symptoms with a degree of severity ranging from a mild, acute illness to death. As if this weren't serious enough, many mycotoxins -- such as aflatoxin -- also are potent carcinogens.  Controlling mold growth early in the food chain is critical since many mycotoxins are stable to the heat of subsequent processing. Because molds are carried in air and soil, complete elimination isn't possible. Still, how food is handled on the farm directly can minimize the growth of molds and, subsequently, the occurrence of mycotoxins. For example, fields must be given adequate moisture (through irrigations) and pest protection because drought and blight leave plants more susceptible to mold. Preliminary research is further revealing that specific soil conditions may reduce the plant's tendency toward mold growth.  Parasites and viruses. Possibly the most familiar parasitic food safety threat is Trichinella spiralis in pork. The incidence of parasites such as Trichina may be enhanced by high-intensity animal agriculture if waste allowed to concentrate in the same areas where animals live and eat. Using formulated mixtures instead of garbage to feed hogs has dramatically reduced the incidence of Trichina in the United States. Domestic agriculture and veterinary practices for feeding and cleanliness also have made the incidence of parasites in other meats and poultry very low.  Fish and seafood commonly contain parasites. Because these foods are still primarily harvested rather than farmed, less control over the source is possible. Instead, more attention is given to post-harvest seafood handling because most parasites can be destroyed by processing/cooking heat and by freezing.  Viruses also are readily destroyed by heat. The ones of greatest concern are hepatitis A and Norwalk virus, which don't enter the food chain at this early stage and are usually the result of contamination by handlers. In the early links of food chain, most viral food safety risks come from seafood.  Some fish and seafood is raised through aquaculture, which offers some degree of control. But, as is the case with parasites, controlling viruses in the open isn't practical. A certain degree of protection is afforded by monitoring known fishing waters for contamination and quarantining them if necessary.  Although not presently occurring in the United States, a problem those in England, Spain and Portugal have been dealing with is Mad Cow Disease, or Bovine Spongiform Encephalopathy (BSE). This infectious disease causes degenerative changes in the brains of cattle, ultimately leading to their death. It is thought to be caused not by a virus, but a prion -- a sort of "pre-virus" consisting of a small piece of protein that isn't destroyed by heat. Scientists don't yet know enough about BSE to determine what makes the prion virulent or the potential effect on humans who eat meat from a BSE-infected animal. The disease is, however, believed to be linked to processing the non-edible portions of sheep into cattle feed. The FDA Center for Veterinary Medicine's current policy does not allow rendered products from sheep and goats over one year of age to be fed to cattle. Import embargoes also are in place to prevent live animals from being imported from countries in which BSE has been found.  Although the government currently has no specific HACCP requirements at the agricultural stage, it is aware of how safety is affected by farming practices and has, in many cases, set up guidelines. In other situations, it is more feasible to establish a control point at a later link in the food safety chain. This would include the next step: from the farm to suppliers. We'll discuss this in Part Two, next month.Back to top<