Artificial preservatives are a group of chemical substances added to food or to certain cosmetics and medications to slow or prevent spoilage, discoloration, or contamination by bacteria and other disease organisms. Most preservatives are categorized by the US government as food additives.
Benzoates. Inhibits the growth of molds, yeasts, and bacteria in acidic drinks and liquids, including fruit juice, vinegar, sparkling drinks, and soft drinks.
Sodium benzoate. Used as an antimicrobial agent in foods with a pH below 3.6, including salad dressings, carbonated drinks, fruit juices, and Oriental food sauces such as soy sauce and duck sauce.
Sorbates. Prevents the growth of molds, yeasts, and fungi in foods or beverages.
Propionates. Inhibits the growth of mold in baked goods.
Nitrites. Prevents the growth of bacteria, particularly Clostridium botulinum (bacterium responsible for botulism), in meat or smoked fish.
Sulfites. Prevents oxidation and inhibits the growth of yeasts and fungi in beer and wines, and preserves meats, dried potato products, and dried fruits.
Vitamin E. Slows oxidation of fresh-cut fruits and vegetables, used to fortify breakfast cereals and pet foods.
Vitamin C. Prevents browning of fresh-cut apples, peaches, and other fruits.
Butylated hydroxyanisole (BHA). Prevents oxidation in butter, lard, meats, baked goods, beer, vegetable oils, potato chips and other snack foods, nuts and nut products, and dry mixes for beverages and desserts. Butylated hydroxytoluene (BHT). Used in fats, oils, shortening, and similar products.
Disodium ethylenediaminetetraacetic acid (EDTA). Delays spoilage (used in food processing).
Polyphosphates. Used as an anti-browning agent in dips and washes for fresh-peeled fruits and vegetables.
Citric acid. Used as a flavoring agent and antioxidant in foods.
As technology advanced, artificial preservatives were designed with the same goal as the earlier methods—to prevent food from spoiling or discoloring. Spoilage usually involves one of two processes: contamination by microorganisms or oxidation. The primary causes of contamination are bacteria, molds, fungi, and yeasts. 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 speed up the process of food spoilage through oxidation. Preservatives that are added to food to prevent oxidation related to these minerals are called chelating agents.
Some antimicrobial preservatives, particularly parabens, are added to medications to prevent the growth of bacteria or fungi. Most of these preparations are topical, which means that they are intended for use on the outside of the body, such as 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 vaccines, other biologicals, and 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.
Because of growing concern about the possible long-term effects of artificial preservatives on the environment as well as human health, researchers are looking into alternative approaches to food preservation and packaging. One proposal involves the use of packaging materials impregnated with antimicrobial compounds; this approach would eliminate the need to add these compounds to the food itself. A second approach involves research into using natural antimicrobial compounds to protect food from spoilage. These compounds include plant extracts, essential oils, enzymes, peptides, bacteriocins (compounds produced by bacteria that inhibit the growth of closely related bacteria), and fermented ingredients.
To gain FDA approval, producers of artificial preservatives must submit an application to show:
In 2011, Congress passed the FDA Food Safety Modernization Act (FSMA), a piece of legislation that expands the FDA's powers to prevent contamination of the food supply rather than simply respond to outbreaks of foodborne illnesses after they occur. FSMA gives the agency comprehensive authority to require preventive measures not only across the food industry in the United States, but also to hold imported food products to the same standards as domestic foods.
The three major groups of artificial food preservatives include antimicrobial agents, antioxidants, and chelating agents.
Antimicrobial preservatives are added to food, cosmetics, and some pharmaceuticals to destroy bacteria or to inhibit the growth of mold.
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). A substance's pH value is a measure of its acidity or alkalinity. Solutions with a pH below 7 are considered acidic, and those above 7 are alkaline. Potassium benzoate is used to inhibit the growth of molds, yeasts, and bacteria in some processed foods and beverages, including fruit juice and sparkling drinks. Potassium benzoate is used most commonly in soft drinks. It is listed on some products as being used to protect taste and preserve freshness. When potassium benzoate is dissolved into liquid, it breaks down into sodium benzoate and the electrolyte potassium.
Sodium benzoate can be produced commercially by reacting sodium hydroxide with benzoic acid. It is used as an antimicrobial agent in foods with a pH below 3.6, such as salad dressings, carbonated drinks, fruit juices, and such Asian food sauces as soy sauce and duck sauce. It is also used in some mouthwashes. Sodium benzoate occurs naturally in cranberries, prunes, greengage plums, cloves, cinnamon, and apples. Although the FDA limits the concentration of sodium benzoate as a preservative to 0.1%, organically grown cranberries and prunes may contain higher levels.
When sodium benzoate is added to beverages that contain vitamin C (ascorbic acid), the combination could produce small amounts of benzene, a chemical known to cause leukemia and other cancers at high levels of exposure. Though the amounts present in foods and beverages are very small, the FDA has worked with manufacturers to keep levels below 5 parts per billion (ppb), the acceptable amount established by the U.S. Environmental Protection Agency (EPA) for benzene in drinking water.
PARABENS. Parabens are a group of parahydroxybenzoates that have been used as preservatives for a long time in cosmetics and pharmaceuticals to prevent the growth of bacteria and molds. They do not have antiviral activity. Parabens can be found in toothpaste, moisturizers, makeup, tanning lotions, shaving cream, and hand lotion as well as in topical pharmaceuticals and vaccines. The most common parabens used in the manufacture of drugs and cosmetics are methylparaben, propylparaben, butylparaben, and ethylparaben.
Parabens are generally considered safe for use by regulatory agencies in Europe as well as the United States. The FDA reported at the end of 2017 that there is no evidence linking parabens to breast cancer or other forms of cancer. A small minority of consumers who are allergic to parabens may develop skin rashes, but the compounds are considered nonirritating and nonsensitizing for most people. The chief concern about parabens as of 2018 is their tendency to accumulate in community wastewater and to require special treatment to remove them from the water supply.
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%–0.10%. Potassium sorbate, which is made by reacting sorbic acid with potassium hydroxide, is a mild preservative. It is often used to stabilize wine as well as to prevent the growth of molds in cheese, yogurt, dry fruit, jelly, syrup, and baked goods such as cake. 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. They are used to inhibit the growth of mold in baked goods such as bread, cakes, pies, and rolls. The propionates are often used instead of benzoates in bakery products because they do not require an acidic environment to be effective. Calcium propionate is also added to animal feed to prevent milk fever in cows.
NITRITES. Nitrites are salts of nitrous acid that were used more often in the past for curing meat than they are in the twenty-first century. 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. The first reason is that they are toxic in large amounts; a lethal dose of nitrites for a human is 22 mg per kg of body weight. The second reason is that 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. For a manufacturer to be permitted to use sodium 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.
It is highly unlikely that a person would consume a lethal amount of nitrites through food, but according to the American Cancer Society and the World Cancer Research Fund, studies have linked eating large amounts of processed meats, which contain nitrites, with an increased risk of colorectal cancer. Nitrites also occur naturally in fruits, grains, and vegetables, especially root vegetables.
Antioxidants are preservatives added to oils and fatty foods to prevent them from becoming rancid.
SULFITES. The sulfites are a group of compounds containing charged molecules of sulfur compounded with oxygen. There are five used as 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. People with asthma or allergies to aspirin are at an elevated risk for this type of reaction. 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. Another issue that has been reported with sulfites is their tendency to eliminate normal bacteria in the digestive tract that aid in the process of digestion. This loss of beneficial intestinal flora occurs even at the low concentration of sulfites regarded as safe for use in food.
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.
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) of the Department of Health and Human Services (HHS) listed it in 2011 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 1,000 ppm.
BUTYLATED HYDROXYTOLUENE (BHT). BHT is similar to BHA in its structure and is used 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. The FDA first approved it as a food preservative in 1954. BHT has been banned in Japan, Romania, Sweden, and Australia but not in the United States. Although the use of BHT is controversial, it has not been shown conclusively to be carcinogenic.
Chelating agents work by binding or sequestering metal ions, usually iron or copper, in certain foods to prevent the metals from oxidizing and speeding up spoilage.
POLYPHOSPHATES. Polyphosphates are chelating agents with limited solubility in cold water that are used in low concentrations (0.5%–2%) as anti-browning agents in dips and washes for fresh-peeled fruits and vegetables. They are also used to soften water and to remove mineral deposits from beverage production 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.
The categorization of a 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 since been greatly restricted in their permissible uses. Information about the current status of more than 3,900 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 the U.S. Food and Drug Administration's EAFUS (Everything Added to Food in the United States) database.
Some people may wish to avoid eating meat containing nitrites such as bacon, sausage, and ham. Although no studies have proven that nitrites cause cancer, people concerned about the effects of nitrites or nitrates should consult their doctor. Studies have indicated a link between consuming large amounts of processed meat and an increased risk of colorectal cancer, but it is not known as of 2018 whether nitrites are the cause or if other factors contribute to the risk. Nitrosamines, however, are known carcinogens, and may be produced when nitrites are combined with other substances, especially protein.
Some hypersensitivity reactions to food preservatives occur in relation to food eaten in 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.
Allergic reactions to artificial preservatives (or coloring or flavoring additives) in food may involve the skin (flushing, itching, or rashes); the digestive system (nausea, vomiting, or diarrhea); the respiratory system (wheezing, cough, or runny nose); or the muscles (cramping or aching sensations). Some doctors think that reactions to food additives are underdiagnosed because they are not often suspected; most maintain, however, that hypersensitivity to food additives involves at most 1% of the adult population and perhaps 2% of children.
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. 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.
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 such as blood pressure and pulse rate. A sudden and significant drop in lung function indicates that the patient is sensitive 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.
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 could try growing their own produce or purchasing organic fresh fruits and vegetables or those from local farmers during the growing season.
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.
See also Food additives ; Food allergies ; Sugar ; Vitamin C ; Vitamin E .
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Rebecca J. Frey, PhD