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Food doesn't last.

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In days, sometimes hours,
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
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
and are they safe?

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

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microbes and oxidation.

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Microbes like bacteria and fungi
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,
slimy, moldy mess.

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

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caused by enzymes or free radicals
which turn fats rancid

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and brown produce, 
like apples and potatoes.

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Preservatives can prevent both types
of deterioration.

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Before the invention of artificial
refrigeration,

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fungi and bacteria could 
run rampant in food.

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

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For example, making the food more acidic
unravels enzymes

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that microbes need to survive.

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And some types of bacteria 
can actually help.

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For thousands of years, people preserved
food using bacteria

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that produce lactic acid.

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The acid turns perishable vegetables
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
digestive track with beneficial microbes.

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Many synthetic preservatives 
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,
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
perfectly safe.

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Another antimicrobial strategy is to add
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
that microbes need to grow

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and actually suck moisture out
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
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 
are best in moderation.

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Antimicrobial nitrates and nitrites,
often found in cured meats,

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ward off the bacteria that cause botulism,
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
may be the culprit.

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Meanwhile, antioxidant preservatives
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
for millennia

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

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Combining smoking with salting was an
effective way of preserving meat

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before refrigeration.

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For antioxidant activity 
without a smoky flavor,

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there are compounds like BHT
and tocopherol,

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better known as vitamin E.

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Like the compounds in smoke,
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
and ascorbic acid

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help cut produce keep its color

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by thwarting the enzyme 
that causes browning.

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Some compounds 
like sulfites can multitask.

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They're both antimicrobials
and antioxidants.

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Sulfites may cause allergy symptoms
in some people,

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but most antioxidant preservatives
are generally recognized as safe.

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So should you be worried 
about preservatives?

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

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because they're used 
in very small amounts

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determined by the FDA to be safe.

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Nevertheless, some consumers
and companies

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are trying to find alternatives.

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Packaging tricks, like reducing
the oxygen around the food can help,

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but without some kind 
of chemical assistance,

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