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Artificial preservatives are a group of chemical substances added to food, sprayed on the outside of food, or added to certain medications to retard spoilage, discoloration, or contamination by bacteria and other disease organisms. Most preservatives are categorized by the federal government as food additives, which are defined by the Federal Food, Drug, and Cosmetic Act (FD&C) of 1938 as “any substance, the intended use of which results directly or indirectly, in its becoming a component or otherwise affecting the characteristics of food.” A subcategory of food preservatives are classified as generally recognized as safe (GRAS), which means that the government accepts the current scientific consensus on their safety, based on either their use prior to 1958 or to well-known scientific information.
The categorization of any artificial preservative is never permanent; it may change as new information about the preservative’s safety is reported and analyzed. Certain preservatives that were once considered safe—most notably sulfites and nitrites—have been banned in recent years or greatly restricted in their permissible uses. Information about the current status of more than three thousand substances (including coloring and flavoring agents as well as preservatives) that the FDA has either approved as food additives or listed or affirmed as GRAS may be obtained from EAFUS, an online database maintained by the FDA’s Center for Food Safety and Applied Nutrition.
The types of artificial preservatives, their role in food preservation, and foods containing preservatives. (Illustration by GGS Information Services/Thomson Gale.)
(CFSAN). EAFUS is an acronym for “Everything Added to Food in the United States.”
Artificial preservatives as used in the early 2000s are an extension of centuries-old methods of food preservation, some of which involved adding naturally occurring chemicals to food. To keep food from spoiling before it could be eaten, early humans found ways to dry it or (in colder climates) freeze it. Drying or dehydrating foods, a process known as desiccation, worked well with fruits, herbs, some meats, and some vegetables. Another method for preserving fruit was sugar preservation, which involved cooking the fruit in a high concentration of sugar that discouraged the growth of bacteria. In terms of natural chemicals, vinegar, ethanol (beverage alcohol), olive oil, and salt have been used for centuries to preserve foods by pickling, while meats and some types of fish have been preserved by smoking and curing, which draws moisture from the meat without cooking it. Smoking introduces antioxidants into meat or fish, while some spices used to flavor foods, such as curries and hot chilies, contain antimicrobial compounds.
The purpose of the major groups of artificial preservatives is to prevent food from spoiling or discoloring during the time it takes to transport the food from the producer to the consumer—including storage time in a restaurant or the individual consumer’s home. Spoilage usually involves one of two processes: contaminationby microorganisms (bacteria, molds, fungi, and yeasts are the primary offenders) or oxidation. Oxidation is the scientific name for the process that takes place in some foods when they combine with the oxygen in the atmosphere in the presence of heat, light, or certain metals. Oxidized foods typically turn brown, develop black spots, or acquire a bad or “off” smell. Cooking oils, oily foods like potato chips, sausage, or nuts, or buttery spreads that develop an unpleasant taste or smell are said to have gone rancid. Some minerals in food—particularly iron and copper—can also speed up the process of food spoilage through oxidation. Preservatives added to food to prevent oxidation related to theseminerals are called chelating agents.
Some antimicrobial preservatives are added to medications to prevent the growth of bacteria in them. Most of these preparations are topical, which means that they are intended for use on the outside of the body—the skin, the eyes, or the ears. Eye drops formulated to relieve dry eyes are the most common topical medications that may contain artificial preservatives, but some asthma drugs also contain benzoates or other antimicrobials. Sulfites (sometimes spelled sulphites) are added to asthma inhalers, injectable epinephrine, and some other medications to prevent browning of the solution.
Artificial food preservatives can be divided into three major groups, antimicrobial agents, antioxidants,and chelating agents.
Antimicrobial preservatives are added to food to destroy bacteria or to inhibit the growth of mold on foods.
BENZOATES. Benzoates are salts of benzoic acid, a weak acid that was at one time derived from benzoin resin, a gum obtained from the bark of trees native to Thailand and Indonesia. The benzoates used as food preservatives are potassium benzoate and sodium benzoate. Potassium benzoate works best in products with a low pH (below 4.5); it is used to inhibit the growth of molds, yeasts, and bacteria in acidic drinks and liquids, including fruit juice, vinegar, sparkling drinks, and soft drinks.
SORBATES. The sorbates are a group of antimicrobial food preservatives comprising sorbic acid and its three mineral salts, potassium sorbate, calcium sorbate, and sodium sorbate. The name of the group comes from the botanical name of the rowan tree, Sorbus aucuparia, because sorbic acid was first isolated from unripe rowan berries. In general, food manufacturers prefer the three salts of sorbic acid to the acid itself because they are easier to dissolve in water.
The sorbates are used to prevent the growth of molds, yeasts, and fungi in foods or beverages with a pH below 6.5. They are generally used at concentrations of 0.025 percent–0.10 percent. Potassium sorbate, which is made by reacting sorbic acid with potassium hydroxide, is a mild preservative that is often used to stabilize wine as well as to prevent the growth of molds in cheese, yogurt, and baked goods. Allergic reactions to the sorbates are uncommon and limited to minor skin rashes or itching.
PROPIONATES. Propionates are salts of propionic acid. The three propionates most commonly used as food preservatives are calcium propionate, sodium propionate, and potassium propionate, used to inhibit the growth of mold in baked goods. Calcium propionate is also added to animal feed to prevent milk fever in cows. The propionates are often used instead of benzoates in bakery products because they do not require an acidic environment to be effective.
NITRITES. Nitrites are salts of nitrous acid that were used more often in the past for curing meat than they are now. The most commonly used nitrite in food preservation is sodium nitrite. When added to meat or smoked fish, it prevents the growth of bacteria, particularly Clostridium botulinum, the bacterium responsible for botulism, a potentially deadly disease. Sodium nitrite also turns meat an appealing dark red color when it interacts with myoglobin, the primary oxygen-carrying pigment in muscle tissue.
Nitrites are being gradually phased out of food processing for two reasons. First, they are themselves toxic in large amounts; a lethal dose of nitrites for a human being is 22 mg per kg of body weight. Second, nitrites in meat can react with the breakdown products of amino acids in the acidic environment of the human stomach to form nitrosamines, substances that are known to be carcinogenic. To be permitted to usesodium nitrite to prevent the growth of C. botulinum in smoked fish or meat, the manufacturer must show that the maximum amount of nitrite in the food will be no more than 200 parts per million (ppm). Sodium ascorbate, a salt of ascorbic acid (vitamin C), is often added to foods containing nitrites to inhibit or prevent the formation of nitrosamines.
SULFITES. The sulfites are a group of compounds containing charged molecules of sulfur compounded with oxygen. There are five used as antioxidant preservatives: sodium sulfite, sodium bisulfite, sodium metabisulfite, potassium bisulfite, and potassium metabisulfite. They are applied to foods as dips or sprays. Sodium metabisulfite and potassium metabisulfite are commonly used to stabilize wine or beer. When added to these fluids, the sulfite compounds release sulfur dioxide gas, which prevents oxidation and also inhibits the growth of yeasts and fungi. Sodium sulfite is used to preserve meats, dried potato products, and dried fruits.
Sulfites have been used for centuries as food preservatives, since they occur naturally in almost all wines. Of all the groups of food preservatives, however, sulfites are the most likely to produce hypersensitivity reactions. Asthmatics and people with allergies to aspirin are at an elevated risk for this type of reaction to sulfites. A severe systemic reaction known as anaphylaxis or anaphylactic shock may be fatal and requires immediate treatment at an emergency room. Anaphylaxis is characterized by hives, difficulty breathing, and cardiovascular collapse.
VITAMIN E. Vitamin E (tocopherol) is a fat-soluble vitamin that occurs as a natural antioxidant in many foods, particularly vegetable oils, whole grains, nuts, wheat germ, and green leafy vegetables. It may be added to fresh-cut fruits and vegetables to slow oxidation. It is also used to fortify some breakfast cereals and pet foods.
VITAMIN C. Vitamin C (ascorbic acid) also occurs naturally in many fruits and vegetables, particularly citrus fruits. It is a water-soluble vitamin. The salts of ascorbic acid—sodium ascorbate, calcium ascorbate, and potassium ascorbate—are also water-soluble and are often added to fresh-cut apples, peaches, and other fruits to prevent browning. These three compounds are not fat-soluble and cannot be used to prevent fats from going rancid. To protect fats or oils from oxidation, a fat-soluble ester of ascorbic acid known as ascorbyl palmitate must be used.
BUTYLATED HYDROXYANISOLE (BHA). BHA, which is a white or slightly yellow waxy solid in its pure form, is widely used in the food industry to prevent oxidation in butter, lard, meats, baked goods, beer, vegetable oils, potato chips and other snack foods, nuts and nut products, dry mixes for beverages and desserts, and many other foods. BHA is also used in cosmetics, particularly lipsticks and eye shadows. It is effective as an antioxidant because oxygen reacts preferentially with it rather than with the fats or oils containing it, thereby protecting them from spoilage. Although the FDA considers BHA a GRAS substance when its content is no greater than 0.02% of the total fat content of the product by weight (200 ppm), the National Toxicology Program (NTP) listed it in 2005 as “reasonably anticipated to be a human carcinogen” on the basis of experimental findings in animals. The NTP stated that the maximum content of BHA in various foods that it sampled ranged from 2 to 1000 ppm.
BUTYLATED HYDROXYTOLUENE (BHT). BHT is similar to BHA in its structure and uses as an antioxidant, although it is ordinarily a white powder rather than a waxy substance at room temperature. BHT is often added to packaging materials as well as directly to fats, oils, shortening, and similar products. It was first approved by the FDA as a food preservative in 1954. BHT has been banned in Japan, Romania, Sweden, and Australia though not in the United States. Although the use of BHT is controversial, it has not been shown conclusively to be carcinogenic as of 2007.
Chelating agents work by binding (or sequestering) metal ions (usually iron or copper) in certain foods in order to prevent the metals from oxidizing and speeding up spoilage of the food.
DISODIUM ETHYLENEDIAMINETETRAACETIC ACID (EDTA) EDTA is used in food processing to bind manganese, cobalt, iron, or copper ions in order to retard spoilage. It is sometimes added to eye drops to reinforce the action of other preservatives. It is also used in dentistry to wash out teeth during root canal procedures and in medicine to treat mercury or lead poisoning. Last, EDTA is added to soft drinks containing both ascorbic acid (vitamin C) and sodium benzoate to prevent the formation of benzene, which is a carcinogen
POLYPHOSPHATES. Polyphosphates are chelating agents with limited solubility in cold water that are used as antibrowning agents in dips and washes for fresh-peeled fruits and vegetables, in low concentrations of 0.5 to 2 percent. They are also used to soften water and to remove mineral deposits from beverageproduction equipment. Polyphosphates are considered nontoxic.
CITRIC ACID. Citric acid, which is found naturally in citrus fruits, can be used not only as a flavoring agent and antioxidant in foods but also as a chelating agent in soaps and detergents. By chelating the minerals that are present in hard water, citric acid allows the cleaning agents to produce foam without the need for added water softeners. Allergic reactions to citric acid are rare; it is regarded as a safe food additive by all major international food regulatory organizations as well as by the FDA, because excess citric acid is easily metabolized by the body and excreted.
Government regulations of artificial preservatives
Artificial preservatives, like other food additives, are strictly regulated by the U.S. Food and Drug Administration (FDA). In 1958 an amendment regarding all categories of food additives was attached to the Food, Drug, and Cosmetic Act of 1938. The 1958 amendment stipulates that a food manufacturer must apply for FDA approval before adding a new preservative to food, before using a different amount of a previously approved preservative, or before using an approved preservative in a different way. The application must show:
In addition, the application for approval must show that the preservative does not deceive consumers by changing the appearance of food. For example, sulfites may not be added to meat because they restore its red color, thus making it look fresh when it may not be in fact.
Consumers who are concerned about a specific artificial preservative in their food can check for its presence by reading the labels of processed foods, which are required by law to state the ingredients in order by weight from the greatest amount to the least. Those who wish to cut down on their intake of preservatives in general can try growing some of their own produce, or purchase fresh fruits and vegetables only from local farmers during the growing season.
EATING OUT. Some hypersensitivity reactions to food preservatives occur in relation to food eaten at restaurants. Restaurant foods are most likely to be the culprit when the person has a reaction to a specific dish served in a restaurant but not to that same food when made at home. People who already know that they are sensitive to sulfites may need to ask about specific dishes at a restaurant ahead of time to inquire whether they are made from foods containing high levels of sulfites.
People allergic to high levels of sulfites should avoid anything containing or garnished with bottled (non-frozen) lemon or lime juice, wine, molasses, grape juices, pickled cocktail onions, dried potatoes, wine vinegar, gravies or sauces, Maraschino cherries, fruit toppings, and sauerkraut. People who are sensitive to moderate or low levels of sulfites should also avoid fresh mushrooms, canned clams, avocado dip or guacamole, pickles and relishes, maple syrup, corn syrup, fresh shrimp, apple cider, and cider vinegar.
MEDICATIONS. People who suspect that they are sensitive to artificial preservatives in eye drops can ask their doctor or pharmacist for a formula made without preservatives. Asthma inhalers that do not contain sulfites are available for asthmatics with sulfite allergies.
No negative interactions between food preservatives and prescription medications have been reported. Some researchers in dentistry, however, are testing the hypothesis that benzoates interact positively with fluoride by reinforcing the effects of fluoride in preventing dental cavities.
Hypersensitivity to food preservatives is usually tested by a food challenge. The patient is given a dietfree of the suspected additive for a week or two and then given foods containing the additive to see whether the symptoms previously reported by the patient recur. If they do, the advice of physicians and researchers in the field is to simply avoid foods or other products containing that preservative.
Testing for sulfite allergy should be done only by a physician who has been trained in this procedure and has some experience in using it. The test involves administering increasing amounts of sulfites by mouth to the patient while the doctor monitors the patient’s lung function and other vital signs (blood pressure, pulse rate, etc.) A sudden and significant drop in lung function indicates that the patient is sensitive to sulfites.
There are no known complications to testing people for hypersensitivity to artificial preservatives in foods or to treating such hypersensitivity by avoiding the additive in question.
In general, food preservatives are no more likely to cause allergic reactions in children than either coloring agents or flavoring agents, which are the other major categories of food additives. Some people develop hives, itching, or nasal congestion when exposed to one particular type of yellow food coloring, FD&C 5, known as tartrazine. Monosodium glutamate (MSG), a food additive sold under the trade name of Accent, is also added to soups, broths, and some restaurant dishes to intensify the flavors already present in the food. Although MSG was reported to cause headaches, dry mouth, and asthma attacks in some people—a group of symptoms referred to as “Chinese restaurant syndrome” since the late 1960s, recent double-blind studies indicate that there is no causal connection between MSG and the reported symptoms.
The food preservatives most likely to cause allergic reactions are the sulfites and the benzoates. Prior to 1986, sulfites were commonly added to fresh produce in supermarkets and on restaurant salad bars to prevent browning. Reports of sensitivity reactions, however, led the FDA to ban the use of sulfites on fresh produce, especially lettuce put out on salad bars. As of 2007, the FDA requires all foods containing more than 10 ppm of sulfites to declare sulfites on the label. Foods containing less than 10 ppm of sulfites have not been shown to cause allergic symptoms even in people who are hypersensitive to sulfites.
Sodium benzoate has been reported to cause skin rashes or facial swelling in some people when used as a preservative in acidic foods and beverages, and to worsen asthma attacks in some patients taking asthma medications. Reactions to benzoates, however, are a very low percentage of food allergies; one team of physicians in Italy rated reactions to benzoates as no more than 2% of all allergic responses to foods or drugs.
Reporting food-related problems
To report allergic reactions to preservatives or other food additives, consumers should contact the FDA’s consumer complaint coordinator in their geographic area. Links to those persons can be found on the FDA’s website at http://www.fda.gov/opacom/backgrounders/problem.htmlndashfood. If the problem concerns food eaten in or purchased from a restaurant, however, it should be reported to the local or state health department.
With the exception of large quantities of nitrites, no food preservatives approved for use by the FDA or its international counterparts are directly toxic to human beings.
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Rebecca J. Frey, PhD