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Food doesn't last.

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In days, sometimes hours,[br]bread goes moldy,

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apple slices turn brown,

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and bacteria multiply in mayonnaise.

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But you can find all of these foods[br]out on the shelf at the grocery store,

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hopefully unspoiled,

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thanks to preservatives.

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But what exactly are preservatives?

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How do they help keep food edible[br]and are they safe?

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There are two major factors that cause[br]food to go bad:

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microbes and oxidation.

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Microbes like bacteria and fungi[br]invade food

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and feed off its nutrients.

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Some of these can cause diseases,

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like listeria and botulism.

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Others just turn edibles into a smelly,[br]slimy, moldy mess.

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Meanwhile, oxidation is a chemical change[br]in the food's molecules

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caused by enzymes or free radicals[br]which turn fats rancid

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and brown produce, [br]like apples and potatoes.

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Preservatives can prevent both types[br]of deterioration.

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Before the invention of artificial[br]refrigeration,

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fungi and bacteria could [br]run rampant in food.

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So we found ways to create an inhospitable[br]environment for microbes.

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For example, making the food more acidic[br]unravels enzymes

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that microbes need to survive.

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And some types of bacteria [br]can actually help.

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For thousands of years, people preserved[br]food using bacteria

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that produce lactic acid.

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The acid turns perishable vegetables[br]and milk

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into longer lasting foods,

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like sauerkraut in Europe,

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kimchi in Korea,

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and yogurt in the Middle East.

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These cultured foods also populate your[br]digestive track with beneficial microbes.

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Many synthetic preservatives [br]are also acids.

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Benzoic acid in salad dressing,

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sorbic acid in cheese,

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and propionic acid in baked goods.

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Are they safe?

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Some studies suggest that benzoates,[br]related to benzoic acid,

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contribute to hyperactive behavior.

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But the results aren't conclusive.

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Otherwise, these acids seem to be[br]perfectly safe.

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Another antimicrobial strategy is to add[br]a lot of sugar, like in jam,

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or salt, like in salted meats.

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Sugar and salt hold on to water[br]that microbes need to grow

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and actually suck moisture out[br]of any cells that may be hanging around,

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thus destroying them.

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Of course, too much sugar and salt[br]can increase your risk of heart disease,

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diabetes,

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and high blood pressure,

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so these preservatives [br]are best in moderation.

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Antimicrobial nitrates and nitrites,[br]often found in cured meats,

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ward off the bacteria that cause botulism,[br]but they may cause other health problems.

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Some studies linking cured meats to cancer

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have suggested that these preservatives[br]may be the culprit.

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Meanwhile, antioxidant preservatives[br]prevent the chemical changes

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that can give food an off-flavor or color.

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Smoke has been used to preserve food[br]for millennia

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because some of the aromatic compounds[br]in wood smoke are antioxidants.

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Combining smoking with salting was an[br]effective way of preserving meat

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before refrigeration.

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For antioxidant activity [br]without a smoky flavor,

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there are compounds like BHT[br]and tocopherol,

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better known as vitamin E.

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Like the compounds in smoke,[br]these sop up free radicals

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and stave off rancid flavors

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that can develop in foods like oils,

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cheese,

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and cereal.

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Other antioxidants like citric acid[br]and ascorbic acid

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help cut produce keep its color

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by thwarting the enzyme [br]that causes browning.

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Some compounds [br]like sulfites can multitask.

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They're both antimicrobials[br]and antioxidants.

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Sulfites may cause allergy symptoms[br]in some people,

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but most antioxidant preservatives[br]are generally recognized as safe.

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So should you be worried [br]about preservatives?

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Well, they're usually near the end[br]of the ingredients list

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because they're used [br]in very small amounts

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determined by the FDA to be safe.

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Nevertheless, some consumers[br]and companies

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are trying to find alternatives.

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Packaging tricks, like reducing[br]the oxygen around the food can help,

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but without some kind [br]of chemical assistance,

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there are very few foods that can[br]stay shelf stable for long.