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From: Food Quality & Safety magazine, December/January 2007

Are What You Eat Really What They Are

Uncovering Hidden, Unwanted Contents in Food-Species ID Testing as the Industry’s and Consumer’s Ultimate Solution

by Terence L.T. Lau, PhD

BSE is old news. As early as the 17th century, scrapie disease was described in sheep.1 However, the agents causing its sponge-like brain symptoms were not reported until the 1980s, work for which Stanley Prusiner was later to be awarded the Nobel Prize in physiology or medicine. He named the infectious proteins “prions.” After the first recognized case, in 1986, of a prion disease in a British cow, “bovine spongiform encephalopathy” (BSE), bovine cases in the U.K. soared to a peak of 36,680 in 1992 alone.2

A smaller number of BSE infected cows have since been detected in other countries including Ireland, Poland, Spain, Portugal, France, Germany and Switzerland, and also the United States, Canada and Japan. Proposed to have arisen due to the addition of animal protein to feed (presumably including that from scrapie infected sheep), it also resulted in unusual occurrences of a rare, normally hereditary and old-age-related human disease, Creutzfeldt-Jakob disease (CJD), in young people, thus the human form was labeled “variant” CJD (vCJD). These confirmed human cases, which up until the present, number around 160 in the U.K., some of which are presumed to have contracted the prions through consumption of infected meat products.

What if processed foods, which often contain additives produced from animals we do not realize and may not want to consume, are contaminated by, for example, these prions and other pathogens? This worries consumers and brings to the industry many uncertainties; producers and suppliers themselves might not even know whether the food they produce or sell is free from these contents. How then, would the industry be able to provide foods free from targeted organisms or contaminants to better protect itself and boost consumers’ confidence?

Can Government Regulations and Policies Alleviate Such Worries?

Consider again the BSE example. Beef producing and exporting nations were hit very hard by the BSE crisis. During the BSE outbreaks of the 80s and 90s, the U.K. government implemented a mass slaughtering of cow herds in the U.K. and at present, most European countries, including the U.K., state that they test all slaughter cattle over 30 months of age (Japan states that it tests all slaughtered cattle). This is intended to identify infected but asymptomatic animals, and to remove the risk of contaminated meat entering the food chain.3 This testing is approximately $50 per cow. In addition, EU countries have implemented BSE-related control measures on animal feed. In the U.K., there is a comprehensive ban on processed animal proteins in all feed for farmed ruminants, excluding milk powder, processed eggs and egg products.4 Certain blood products may be fed to farmed fish, pigs and poultry. EU regulations meanwhile state that no animal by-products not intended for human consumption may be used in animal feed.5

Despite all the measures put in place to reassure consumers, dangers apparently persist and over the past few years, various scandals have come to light regarding the quality of our food and the constant need for strict controls and more stringent testing procedures. For instance, the common practice of adding water to chicken carcasses, ostensibly to prevent drying out, led in the 1990s to the practice of injecting the carcasses with additive powders and proteins from other animals to enable the carcass to absorb as much water as possible, even up to 50 percent. The proteins were from the cheap waste parts of other animals, often from cows, and were undetectable by the protein detection tests usually used. This practice was first made public in the U.K. by a team from the BBC documentary series, Panorama in 2000.6 They found factories in certain European countries including Germany, Spain and Holland, which imported cheap chicken carcasses from Thailand and Brazil and after treatment, exported the chickens across the EU.

The Need for Species Identification

Apart from cow contents, we could find plenty of examples in our everyday life that tells us how important it is for species identification. For instance, in processed food the characteristics of the product, such as color, odor, taste and texture may all be very different from the original material.

Thailand exports 4 to 5 metric tons of rice every year, more than half of which is jasmine rice, which could be twice as expensive as its counterparts. One would have concerns about the identity of the jasmine rice available on market – whether they contain pure jasmine rice, or are adulterated with other rice types that are much less expensive. Here we could easily understand how species ID could act as a reliable tool in determining the real identity of a rice sample. By the same reasoning, red wines from merlot grapes or cabernet sauvignon could be easily identified from each other.

The colorless, odorless and tasteless solid gelatin is prepared by prolonged boiling of animal skin, connective tissues or bones. Commonly used in the food industry as a stabilizer, thickener and texturizer, gelatin is added into foods such as jams, ice cream, yogurt and margarine. If not clearly labeled, consumers would be unable to tell if they are eating gelatin, which is derived from animal sources. To test for the presence of these contents, we would perform a type of species identification called “animal specific testing” (AS), which we could find widely applicable in the confirmation of animal species present in food to avoid fake products, confirmation of animal species absent in food, for example, to avoid animal diseases like BSE and AIV, to avoid food allergy, or due to religious concerns. It could of course be used also to confirm targeted animal species such as endangered species. Currently the most sensitive and specific testing available for performing AS are molecular methods such as DNA testing, or more specifically, PCR. To understand how powerful this molecular testing tool is, we would need to know what DNA is and the rationale behind DNA testing.

DNA and the Role of DNA Testing in Food

The words “DNA testing” might bring to mind Discovery Channel stories, but these molecular biology technologies are in fact routinely used in medical science and more recently by food inspection agencies. As a general background, DNA is the hereditary material found in all living things, including animals, plants and bacteria, and in some non-living things, such as viruses, and is different for every species of organism. For food testing, a DNA copying technique known as the “polymerase chain reaction” (PCR) is used. In this method, a stretch of DNA of known sequence for a particular species, e.g. sheep, is chosen. Very short stretches of DNA sequence, “primers,” which can match part of this sequence on the sheep DNA to be copied are made synthetically. These primers are only half a DNA ladder, as if the ladder has been cut longitudinally down the center of the rungs.

DNA is then extracted from the foodstuff and put into a reaction mix. This mix contains the sheep-specific primers and also molecules normally found inside a cell, capable of copying the DNA. Under highly specific reaction conditions, the DNA from the foodstuff also divides into two longitudinal halves and the primers can bind to the region they match.

Then the DNA is copied. This reaction is repeated many times until the stretch of chosen DNA is present in millions of copies. This DNA can then be detected visually after the addition of a dye. If the result of a PCR reaction turns out to be negative (but the DNA extraction reaction has worked as shown by the successful PCR of DNA known to be present), it usually means that the DNA of that organism is not present in the foodstuff. Using our example, if there is no sheep DNA present, but only that of the cow, then the sheep primers won’t match the cow DNA, therefore they can’t bind, and no copies will be made. Thus, the primers are the crucial element of this reaction, being designed according to the DNA sequence of the organism being tested for. They have to be extremely specific and highly sensitive.

As its name indicates, “DNA testing” cannot determine if the disease causing agents present in food are proteinous. However, by determining the presence of their animal carriers, consumers could, by their choice, avoid consuming food that contains these carrier animals. DNA testing of animal feed could also ensure that only permitted substances are included in the feed product.

Testing for Endangered Species

One notable use of AS in food has come from environmental protection groups. In September 1994, an article published in the scientific journal, Science brought to light a survey on processed whale meat on sale in Japan.7 The group responsible for the research, Earthtrust, had sent a researcher to carry out DNA testing to determine whether processed whale meat, as found in tins on the supermarket shelves, was from endangered species such as humpback and fin whales and so prohibited under the International Whaling Commission rules, or from species which could be legitimately hunted. This study showed that not only endangered whales, but also small cetaceans such as dolphins, were being sold as legitimate whale meat in the supermarkets of Japan. The study moreover demonstrated that wildlife products could be traced not just back to the species, but also to the area of origin, subspecies, sex and lineage. Thus, the animals could be relatively precisely “identified” and were not considered to be of endangered species legitimately captured for research purposes (which are permitted to be later put on the market as meat). Later Japanese studies had less incriminating results, however the danger that some consumers have raised as concerns include the fact that many small cetaceans are highly toxic due to contamination of their meat with heavy metals from pollution of the sea. Since this time, DNA testing has become more widespread in endangered species surveillance, and is now also used by U.S. agencies along the coast of Florida, checking the species of origin of sharks’ fins intended for soup bowls in Asia.8

Testing for Unwanted Animal or Plant Species in Religious Foods Organized DNA testing and surveillance may assist those of certain religions, especially those living in multifaith communities, to adhere to the dietary rules or guidelines of their faith.

Muslims make up around a fifth of the world’s population and can only eat meat designated, “Halal.” This means that meat is from animals, raised on a vegetarian diet, which have been slaughtered in a particular way by a Muslim in the name of Allah. DNA testing conducted would show if a (protein-enriched) vegetarian animal feed was really what it said on the packet. Used for a whole range of human consumables, this type of AS testing could encourage safer farming and food production, and deter rogue, unsafe or casual practices. Hindu (no beef, and in some upper castes, no mushrooms, leeks, onions or garlic), Judaism (no pork, no mixing of dairy and meat products), Islam (no pork), and those on strict vegetarian or vegan diets may be aided by AS as well.

Of course DNA testing has no role in the verification of slaughter methods so crucial to Jewish and Muslim communities; however it can aid in the detection of bogus Halal or Kosher certification through the detection of prohibited animal products, including in apparently vegetarian articles such as ice cream, (which may contain mono- and di-glycerides as emulsifiers), bread, cookies and toothpaste. The source of the enzyme rennet used in cheese-making, and gelatin found in marshmallows and in many other products such as yogurt, might also be detected this way. This is because the purification techniques used when obtaining these additives will rarely exclude the DNA of the organism from which the protein or fatty acid was taken, so that a small amount of DNA will be present in the finished foodstuff. Fifty-four countries of the world are Muslim and many of these accept Halal food imports from other non-Muslim countries. DNA testing can hence aid in the verification of these products.

DNA Testing as the Ultimate Solution to Uncovering Hidden Contents

From the surveillance of meat products, processed foods to wildlife protection, we could see that the potential uses of species ID is wide and yet to be explored. The issue here remains that most consumers want to know that what he or she has purchased is actually what it purports to be, and that manufacturers, importers and exporters would also like to ensure what they sell is safe for consumers and that the products could go through the customs smoothly to be delivered on time. Food testing agencies will continue to ensure that the food products sold are free from adulteration with other meats of unspecified species and place of origin unless clearly stated on the label. Therefore, food manufacturers should consider utilizing the most sensitive and reliable tool to ensure the quality of their products from sourcing to marketing.

References:

  1. Brown P, Bradley R. 1755 and all that: a historical primer of transmissible spongiform encephalopathy. BMJ, 1998: 317 (7174); 1688-92.
  2. http://www.defra.gov.org.uk/animalh/bse/ index.html
  3. http://www.fao.org/ag/againfo/subjects/en/ health/bse/he_slaughter.html
  4. http://www.defra.gov.org/animalh/bse/animal-health/feedbanguide.pdf
  5. http://ec.europa.eu/food/food/controls/feedfood/bse_feed_en.htm
  6. http://news.bbc.co.uk/1/hi/programmes/ panorama/3035139.stm
  7. Baker CS and Palumbi SR, Which Whales Are Hunted? A Molecular Genetic Approach to Monitoring Whaling. Science, 1994: 265; 1538-39.
  8. Clarke SC, Magnussen JE, Abercrombie DL, McAllister MK, Shivji MS. Identification of shark species composition and proportion in the Hong Kong shark fin market based on molecular genetics and trade records. Conserv. Biol. 2006: 20; 201-11.

Terence L.T. LAU, Ph.D. is the chief scientific officer and general manager at HKDNA Chips Limited (Hong Kong). Reach him at terence.lau@hkdnachips.com or (852) 2111-2123.

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