A preservative is a substance or a chemical that is added to products such as food, beverages, pharmaceutical drugs, paints, biological samples, cosmetics, wood, and many other products to prevent decomposition by microbial growth or by undesirable chemical changes. In general, preservation is implemented in two modes, chemical and physical. Chemical preservation entails adding chemical compounds to the product. Physical preservation entails processes such as refrigeration or drying. Preservative food additives reduce the risk of foodborne infections, decrease microbial spoilage, and preserve fresh attributes and nutritional quality. Some physical techniques for food preservation include dehydration, UV-C radiation, freeze-drying, and refrigeration. Chemical preservation and physical preservation techniques are sometimes combined.
Antimicrobial preservatives prevent degradation by bacteria. This method is the most traditional and ancient type of preserving—ancient methods such as pickling and adding honey prevent microorganism growth by modifying the pH level. The most commonly used antimicrobial preservative is lactic acid. Common antimicrobial preservatives are presented in the table. Nitrates and nitrites are also antimicrobial. The detailed mechanism of these chemical compounds range from inhibiting growth of the bacteria to the inhibition of specific enzymes.
|E number||chemical compound||comment|
|E200 – E203||sorbic acid, sodium sorbate and sorbates||common for cheese, wine, baked goods|
|E210 – E213||benzoic acid, sodium benzoate and benzoates||used in acidic foods such as jams, salad dressing, juices, pickles, carbonated drinks, soy sauce|
|E214 – E219||hydroxybenzoate and derivatives||stable at a broad pH range|
|E220 – E227||sulfur dioxide and sulfites||common for fruits|
|E249 – E250||nitrite||used in meats to prevent botulism toxin|
|E251 – E252||nitrate||used in meats|
|E280 – E283||propionic acid and sodium propionate||baked goods|
The oxidation process spoils most food, especially those with a high fat content. Fats quickly turn rancid when exposed to oxygen. Antioxidants prevent or inhibit the oxidation process. The most common antioxidant additives are ascorbic acid (vitamin C ) and ascorbates. Thus, antioxidants are commonly added to oils, cheese, and chips. Other antioxidants include the phenol derivatives BHA, BHT, TBHQ and propyl gallate. These agents suppress the formation of hydroperoxides. Other preservatives include ethanol and methylchloroisothiazolinone.
|E number||chemical compound||comment|
|E300-304||ascorbic acid, sodium ascorbate||cheese, chips|
|E321||butylated hydroxytoluene, butylated hydroxyanisole||also used in food packaging|
|E310-312||gallic acid and sodium gallate||oxygen scavenger|
|E220 – E227||sulfur dioxide and sulfites||beverages, wine|
|E306 – E309||tocopherols||vitamin E activity|
A variety of agents are added to sequester (deactivate) metal ions that otherwise catalyze the oxidation of fats. Common sequestering agents are disodium EDTA, citric acid (and citrates), tartaric acid, and lecithin.
Nonsynthetic compounds for food preservation
Citric and ascorbic acids target enzymes that degrade fruits and vegetables, e.g., mono/polyphenol oxidase which turns surfaces of cut apples and potatoes brown. Ascorbic acid and tocopherol, which are vitamins, are common preservatives. Smoking entails exposing food to a variety of phenols, which are antioxidants. Natural preservatives include rosemary and oregano extract, hops, salt, sugar, vinegar, alcohol, diatomaceous earth and castor oil.
Traditional preservatives, such as sodium benzoate have raised health concerns in the past. Benzoate was shown in a study to cause hypersensitivity in some asthma sufferers. This has caused reexamination of natural preservatives which occur in vegetables.
History and methods
Preservatives have been used since prehistoric times. Smoked meat for example has phenols and other chemicals that delay spoilage. The preservation of foods has evolved greatly over the centuries and has been instrumental in increasing food security. The use of preservatives other than traditional oils, salts, paints, etc. in food began in the late 19th century, but was not widespread until the 20th century.
The use of food preservatives varies greatly depending on the country. Many developing countries that do not have strong governments to regulate food additives face either harmful levels of preservatives in foods or a complete avoidance of foods that are considered unnatural or foreign. These countries have also proven useful in case studies surrounding chemical preservatives, as they have been only recently introduced. In urban slums of highly populated countries, the knowledge about contents of food tends to be extremely low, despite consumption of these imported foods.
In ancient times the sun and wind naturally dried out foods. Middle Eastern and Oriental cultures started drying foods in 1,200 B.C. in the sun. The Romans used a lot of dry fruit. In the Middle Ages, the people made “still houses” where fruits, vegetables, and herbs were could dry out in climates that did not have strong sunlight for drying. Sometimes fires were made to create heat to dry foods. Drying prevents yeasts and bread molds (Rhizopus) from growing by removing moisture so bacteria cannot grow.
Cellars, caves, and cool streams were used for freezing. American estates had ice houses built to store ice and food on the ice. Icehouse was then converted to an “icebox”. Icebox was converted in the 1800s to mechanical refrigeration. Clarence Birdseye found in the 1800s that freezing meats and vegetables at a low temperature made them taste better.
Fermenting was discovered when a few grains of barley were left in the rain and turned into beer. Microorganisms ferment the starch-derived sugars into alcohols. This is also how fruits are fermented into wine and cabbage into Kimchi or sauerkraut. Anthropologists believe that as early as 10,000 B.C people began to settle and grow barley. They began to make beer and believed that it was a gift from gods. It was used to preserve foods and to create more nutritious foods from less desirable ingredients. Vitamins are produced through fermentation by microorganisms making the end product more nutritious.
Pickling occurs when foods are placed in a container with vinegar or another acid. It is thought that pickling came about when people used to place food in wine or beer to preserve it due to them having a low pH. Containers had to be stoneware or glass (vinegar will dissolve metal from pots). After the food was eaten, the pickling brine had other uses. Romans would make a concentrated pickle sauce called “garum”. It was very concentrated and the dish that it would be used in would only need a few drops to get the fish taste. Due to new foods arriving from Europe in the 16th century, food preservation increased. Ketchup originated from Europe as an oriental fish brine and when it made it to America, sugar was added. Pickling sauces were soon part of many recipes such as chutneys, relish, piccalilli, mustard, and ketchup when different spices were added to them.
The beginning of curing was done through dehydration. Salting was used by early cultures to help desiccate foods. Many different salts were used from different places such as rock salt, sea salt, spiced salt, etc.. People began to experiment and found in the 1800s that some salts gave meat an appealing red color instead of the grey that they were used to. During their experimenting in the 1920s they realized this mixture of salts were nitrates (saltpeter) that prevented Clostridium botulinum growth.
Jam and Jelly
The early cultures also used honey or sugar as a preservative. Greece used a quince and honey mixture with a slight amount of drying and then tightly packed into jars. The Romans used the same technique but instead cooked the honey and quince mixture to make a solid texture. The Indian and Oriental traders brought sugarcane to the northern climates where housewives were then able to learn to make preservatives by heating fruit with the sugarcane.
Canning started in 1790 from a French confectioner, Nicolas Appert, when he found that by applying heat to food in sealed glass bottles, the food is free from spoilage. Appert’s ideas were tried by the French Navy with meat, vegetables, fruit, and milk in 1806. An Englishman, Peter Durand decided to use Appert’s method on tin cans in 1810. Even though Appert found a method that worked, he did not understand why it worked because many believed that the lack of air caused the preservation. In 1864 Louis Pasteur linked food spoilage/illness to microorganisms.Different foods are placed into jars or cans and heated to a microorganism and inactivating enzyme temperature. They are then cooled forming a vacuum seal which prevents microorganisms from contaminating the foods.
Public awareness of food preservation
Public awareness of food preservatives is uneven. Americans have a perception that food-borne illnesses happen more often in other countries. This may be true, but the occurrence of illnesses, hospitalizations, and deaths are still high. It is estimated by the Center for Disease Control (CDC) that each year there are 76 million illnesses, 325,000 hospitalizations, and 5,000 deaths linked to food-borne illness.
The increasing demand for ready-to-eat fresh food products has led to challenges for food distributors regarding the safety and quality of their foods. Artificial preservatives meet some of these challenges by preserving freshness for longer periods of time, but these preservatives can cause negative side-effects as well. Sodium nitrite is a preservative used in lunch meats, hams, sausages, hot dogs, and bacon to prevent botulism. It serves the important function of controlling the bacteria that cause botulism, but sodium nitrite can react with proteins, or during cooking at high heats, to form carcinogenic N-nitrosamines. It has also been linked to cancer in lab animals. The commonly used sodium benzoate has been found to extend the shelf life of bottled tomato paste to 40 weeks without loss of quality. However, it can form the carcinogen benzene when combined with vitamin C. Many food manufacturers have reformed their products to eliminate this combination, but a risk still exists. Consumption of sodium benzoate may also cause hyperactivity. For over 30 years, there has been a debate about whether or not preservatives and other food additives can cause hyperactivity. Studies have found that there may be increases in hyperactivity amongst children who consume artificial colorings and benzoate preservatives and who are already genetically predisposed to hyperactivity, but these studies were not entirely conclusive. Hyperactivity only increased moderately, and it was not determined if the preservatives, colorings, or a combination of the two were responsible for the increase.
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