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The Science of Food Preservatives

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Modern chemical additives often get a bad rap, but do they deserve it?
By Robert L . Wolke

On the labels of many packaged foods these days, it’s not unusual to see more ingredients that the product does not contain than those it does: “Gluten-free, lactose-free, sugar-free. No MSG, no trans fats, no artificial flavors, no preservatives… ” Some of these labels are meant to convey the message, “Contains no bad stuff.” The message panders to the people who presume that anything added to a processed food-an additive-is not “natural” and should therefore be shunned. But let’s take a closer look at one of those additives, namely chemical preservatives. Are they bad for us? Or are they just the inevitable consequence of societal evolution?

When good food goes bad
Mother Nature has some pretty harsh rules. We may eat only our fellow living organisms-plants and animals-and to do so, we must take their lives. But the instant living organisms die, nature’s chemical and biological cleanup squads kick in, and foods begin to deteriorate, gradually becoming “spoiled,” or unfit to eat. Microscopic bacteria such as Clostridium botulinum will feast on proteins, leaving behind their botulinum toxin, the most acutely toxic substance known. Molds and yeasts ferment carbohydrates, turning them sour. Heat and oxygen turn fats rancid. Enzymes in the foods themselves speed their breakdown and ultimate decay.

Over the past few thousand years, we humans have come up with a variety of ways of keeping our hard-won harvest in an edible, tasty, nontoxic condition. Remarkably, all these methods-still in use today-were devised long before the discovery of bacteria in the 17th century. What’s more, several of these methods not only preserve foods, but they also enhance or improve their flavors

Brave new world
In the past 60 years or so, the world of food has changed drastically. As the ever-growing global population has shifted from rural to more urban living, food buying has become detached from food production as the supermarket has replaced the home garden or farm. Now that most of the world’s population is consuming widely distributed packaged foods, commercial food manufacturers often have to add preservatives directly to foods to keep them fresh and attractive during weeks of shipping and shelf display before the consumer even opens the jars or cans. And once they are open, preservatives (along with cosmetic additives) have to keep the food looking good.

Food scientists have a huge arsenal of chemical preservatives at their disposal to do these jobs. About 1,000 food additives are listed in the Codex Alimentarius, an international (185 member countries) collection of standards and codes of practice relating to foods, food production, and food safety. Of these additives, about 100 are classified as preservatives.

Government oversight
In most developed countries, government agencies are tasked with testing all food additives for safety. In the United States, the Center for Food Safety and Applied Nutrition (CFSAN), a division of the U.S. Food and Drug Administration (FDA), employs more than 800 scientists who continually test the safety of domestic and imported foods. Can we trust these scientific watchdogs? It depends on whom you ask. Inevitably in our contentious society, there are some who do and some who don’t.

Ancient preservation methods
Cooking was probably discovered shortly after the discovery of fire, some hundreds of thousands of years ago. Temperatures above about 165°F kill almost all microorganisms.

Boiling in water is a very effective sterilizer.

Sugaring is the process by which a concentrated solution of sugar extracts water from bacterial cells, thereby dehydrating them. Bacteria cannot survive without water.

Salting or brining has been used to preserve foods since around 2000 B.C. Just as sugar does, salt, or salt solutions, extract water from bacterial cells by osmosis, dehydrating and killing the bacteria.

Cooling or freezing slows all bacterial growth and chemical reactions.

Curing, or treating with nitrites, kills bacteria and adds flavor and color (for example, to bacon or ham).

Fermenting happens when beneficial lactic acid bacteria and yeasts drive out pathogenic organisms, producing alcohol and pleasing flavor(wine, beer, sauerkraut, kimchi, yogurt).

Pickling calls for soaking foods in vinegar or salt water. Most bacteria cannot grow in acidic or highly salty environments.

Poaching or sealing in fat, as in confit or rillettes, prevents oxidation by protecting the food from air.

Drying kills bacteria, molds, and yeasts, which cannot live without water.

Smoking, one of the oldest treatments, is a byproduct of cooking over fire. This process dries meats and fish while imparting unique flavors.

Modern chemical preservatives
Antimicrobials inhibit the growth of bacteria, molds, and yeasts. Sulfites, including sulfur dioxide, are used in dried fruits, fruit juices, vinegars, and wines. Calcium propionate inhibits molds and bacteria in baked goods. Its progenitor, propionic acid, occurs naturally in strawberries, apples, grains, and cheese.

Antifungals such as sodium benzoate, sorbic acid, and parabens prevent mold in beverages, fruit preserves, cheese, pickles, salads, meats, and margarine. Benzoates are found naturally in cranberries, prunes, greengage plums, cinnamon, cloves, and apples, and have been used to preserve foods for about 100 years.

Antioxidants inhibit oxidation by air, which turns fats rancid, by gobbling up the free radicals that participate in oxidation reactions. Antioxidants include sulfites, BHA (butylated hydroxytoluene), TBHQ (tertiary butylated hydroquinone), ascorbic acid, (vitamin C), and propyl gallate.

Enzyme inhibitors slow the natural enzyme-driven ripening and spoilage reactions that begin in fruits and vegetables at harvest. The enzyme phenolase, for example, goes to work as soon as an apple, potato, or banana is cut or bruised, turning it brown and off-flavored. Citric acid and ascorbic acid inhibit phenolase, which cannot function in acidic conditions. Sulfites also inhibit enzymatic degradation reactions in fruits such as raisins and dried apricots.

Sequestrants, also known as chelating agents, tie up atoms of contaminating trace metals such as iron and copper, which catalyze (accelerate) the oxidation and enzyme reactions that cause the discoloration of foods. The most-used chelating agent is EDTA (ethylenediamine tetraacetic acid). Other sequestrants are polyphosphates and citric acid.

Illustration by Neil Webb


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  • 15051987 | 04/14/2015

    Although these chemical preservatives mentioned in the post contribute to the shelf life of the product, would it be hazardous to your health in the long run? And if so, which ones should one try to avoid? Are there chemical preservatives that are considered to be a "healthier" alternative?

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