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

幾天，有時甚至幾小時，麵包就會發霉，蘋果切面會變成棕色，美乃滋中的細菌也會翻倍。

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

但是以上提到的所有食物你都可以在雜貨店的貨架上找到，都是沒有腐壞的，這就多虧了防腐劑。

But what exactly are preservatives?

但是防腐劑到底是什麼東西呢？

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

它是如何讓食物可以食用並且是可以安全食用的呢？

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

造成食物腐壞有兩個主要因素：微生物和氧化作用。

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

微生物如：細菌和真菌會侵入食物，並且以食物的營養為食。

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

其中有些菌類是可能引發疾病的，例如利斯塔氏菌屬和波特淋菌中毒。

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

其他的菌類則會將原本可以食用的食物變成又臭又黏還發霉的糟糕東西。

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.

與此同時，氧化作用是食物分子發生的一種化學反應，是由酶或者是由自由基引起，自由基可以讓脂肪腐壞，讓農產品變成棕色，例如蘋果和馬鈴薯。

Preservatives can prevent both types of deterioration.

防腐劑可以同時防止這兩種破壞的發生。

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

在發明人工製冷以前，真菌和細菌在食物中是肆無忌憚的。

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

因此我們想方設法創造一個讓微生物無法生存的環境。

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

例如，加強食物的酸性以分解酶，這種酶是微生物賴以生存的。

And some types of bacteria can actually help.

有一些細菌確實可以起到幫助的作用。

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

千年以來，人們用產生乳酸的細菌來保存食物。

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

這種酸讓易腐壞的蔬菜和牛奶變成可以保存更久的食物，像是德國泡菜、韓國泡菜，以及中東的酸奶。

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

同時，這些各地的食物可以讓有益的微生物寄居在你的消化道。

Many synthetic preservatives are also acids.

許多人造防腐劑也是酸性的。

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

沙拉調味料中的苯甲酸、奶酪中的山梨酸，以及烘培食物中的丙酸。

Are they safe?

食用它們安全嗎？

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

一些研究指出，與苯甲酸相關的安息香酸鹽，會導致行為亢奮。

But the results aren't conclusive.

但是還沒有定論。

Otherwise, these acids seem to be perfectly safe.

另一方面看，這些酸看起來是完全安全的。

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

另外一種抗微生物的策略就是加大量的糖，如果醬，或者是加鹽，如鹽焗肉。

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.

糖和鹽鎖住食物中的水分，這樣微生物就沒有了賴以生存的水分，實際上，還會吸走活動在細胞周圍的任何水分，達到消滅微生物的目的。

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.

當然，攝入過多的糖和鹽會增加罹患心臟病、糖尿病、高血壓的風險，所以這些防腐劑最好適度使用。

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

抗微生物的硝酸鹽和亞硝酸鹽，通常存在於加工過的肉類中，它可以防止細菌引起波特淋菌中毒，但是它也可能會引起其他的健康問題。

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

一些研究將加工肉和癌症聯繫起來了，並認為這些防腐劑可能是罪魁禍首。

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

同時，抗氧化的防腐劑防止讓食物變味變色的化學變化。

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

用煙燻來保存食物這種方法已經使用了上千年了，因為用來煙燻的木頭中一些香味成份是抗氧化的。

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

在冰箱出現以前，將煙燻和鹽焗結合起來保存肉類是一個十分有效的方法。

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

為了抗氧化同時又沒有煙味，可以用丁基化羻基甲苯和生育酚，更為人熟知的名稱是維他命 E。

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.

就像是煙中的成份，這些會吸走自由基，並且防止酸味產生，以下這些食物有可能會產生酸味：油、奶酪、穀物。

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

其他的抗氧化物如：檸檬酸和維生素C，可以透過阻止引起食物變棕色的酶，幫助食物保持它的顏色。

Some compounds like sulfites can multitask.

一些成份如亞硫酸鹽可以具有多重任務。

They're both antimicrobials and antioxidants.

它同時是抗微生物和抗氧化的。

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

亞硫酸鹽可能會引起一些人的過敏症狀，但是，大部分的防腐劑總的來說是安全可食用的。

So should you be worried about preservatives?

所以你應該擔憂防腐劑的問題嗎？

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.

它們的名稱通常出現在食物原料列表的最後，因為它們的用量十分少，並且防腐劑的安全性是經美國食品藥物管理局確認的。

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

然而一些消費者和公司想要找到替代品。

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.

例如利用包裝的小伎倆，像是減少食物周圍的氧氣，但是如果沒有某些化學物質的幫助，幾乎沒有食物可以在貨架上放那麼長的時間。