In days, sometimes hours, bread goes moldy, apple slices turn brown, and bacteria multiply in mayonnaise.

数日や早ければ数時間でパンにはカビが生え

But you can find all of these foods out on the shelf at the grocery store, hopefully unspoiled, thanks to preservatives.

リンゴの切り口は茶色く変色し

But what exactly are preservatives?

マヨネーズには細菌が繁殖してしまいます

How do they help keep food edible and are they safe?

でもこういう食品がスーパーの棚に並んでいるときは

There are two major factors that cause food to go bad: microbes and oxidation.

まず品質は保たれています

Microbes like bacteria and fungi invade food and feed off its nutrients.

保存料のおかげです

Some of these can cause diseases, like listeria and botulism.

では保存料とは一体何なのでしょうか？

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

どんな仕組みで食べ物を長持ちさせるのかそもそも安全なのでしょうか

Meanwhile, oxidation is a chemical change in the food's molecules caused by enzymes or free radicals which turn fats rancid and brown produce, like apples and potatoes.

食べ物がいたむ要因は主にに2つあります

Preservatives can prevent both types of deterioration.

微生物と酸化です

Before the invention of artificial refrigeration, fungi and bacteria could run rampant in food.

細菌やカビなどの微生物は食べ物に侵入し

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

その栄養分をエサとします

For example, making the food more acidic unravels enzymes that microbes need to survive.

微生物には食中毒を起こす

And some types of bacteria can actually help.

リステリアやボツリヌス菌から

For thousands of years, people preserved food using bacteria that produce lactic acid.

悪臭、ヌメり、カビの元になり食べ物を腐らせるものまであります

The acid turns perishable vegetables and milk into longer lasting foods, like sauerkraut in Europe, kimchi in Korea, and yogurt in the Middle East.

一方、酸化とは食べ物の分子に起こる化学変化のことです

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

酵素やフリーラジカル（遊離基）が原因で脂質を劣化させたり

Many synthetic preservatives are also acids.

リンゴやジャガイモなどの青果物を褐色に変色させたりします

Benzoic acid in salad dressing, sorbic acid in cheese, and propionic acid in baked goods.

保存料を使えばどちらのタイプの品質低下も防ぐことができます

Are they safe?

人工冷蔵の技術が発達する前には

Some studies suggest that benzoates, related to benzoic acid, contribute to hyperactive behavior.

食べ物にカビや細菌がはびこりがちでした

But the results aren't conclusive.

そこで人は微生物が住みにくい環境を作る方法を発見しました

Otherwise, these acids seem to be perfectly safe.

例えば 食べ物の酸性度を上げて

Another antimicrobial strategy is to add a lot of sugar, like in jam, or salt, like in salted meats.

微生物の生存に必要な酵素が分解されるようにしてしまうといった策です

Sugar and salt hold on to water that microbes need to grow and actually suck moisture out of any cells that may be hanging around, thus destroying them.

菌の種類によっては人の役に立つものもあります

Of course, too much sugar and salt can increase your risk of heart disease, diabetes, and high blood pressure, so these preservatives are best in moderation.

何千年にもわたり人間は乳酸を生み出す細菌を使って食べ物の保存をしてきました

Antimicrobial nitrates and nitrites, often found in cured meats, ward off the bacteria that cause botulism, but they may cause other health problems.

乳酸のおかげで 腐りやすい野菜や牛乳が

Some studies linking cured meats to cancer have suggested that these preservatives may be the culprit.

日持ちのする保存食品になります

Meanwhile, antioxidant preservatives prevent the chemical changes that can give food an off-flavor or color.

ヨーロッパのザワークラウト

Smoke has been used to preserve food for millennia because some of the aromatic compounds in wood smoke are antioxidants.

韓国のキムチ

Combining smoking with salting was an effective way of preserving meat before refrigeration.

中東のヨーグルトなどがそうです

For antioxidant activity without a smoky flavor, there are compounds like BHT and tocopherol, better known as vitamin E.

更にこのような発酵食品を摂ると消化器官に善玉菌が住み着きます

Like the compounds in smoke, these sop up free radicals and stave off rancid flavors that can develop in foods like oils, cheese, and cereal.

合成保存料も多くは酸の一種です

Other antioxidants like citric acid and ascorbic acid help cut produce keep its color by thwarting the enzyme that causes browning.

ドレッシングに含まれる安息香酸

Some compounds like sulfites can multitask.

チーズに含まれるソルビン酸

They're both antimicrobials and antioxidants.

洋菓子やパンに含まれる プロピオン酸などがありますが

Sulfites may cause allergy symptoms in some people, but most antioxidant preservatives are generally recognized as safe.

安全性はどうなのでしょうか？

So should you be worried about preservatives?

一部の研究では安息香酸から作られた安息香酸エステルは

Well, they're usually near the end of the ingredients list because they're used in very small amounts determined by the FDA to be safe.

多動性行動を起こす一因子であることを示唆していますが

Nevertheless, some consumers and companies are trying to find alternatives.

はっきりとした結論は出ていません

Packaging tricks, like reducing the oxygen around the food can help, but without some kind of chemical assistance, there are very few foods that can stay shelf stable for long.

それ以外では 完全に無害であるといえるようです