Placeholder Image

字幕列表 影片播放

  • Honey. Youve met honey. It’s that sticky, sweet stuff.

  • Basically just slightly liquidy sugar in a plastic bear bottle, right?

  • Wrong! Honey is a supercharged bacteria-killing powerhouse. And it’s all down to what those

  • hardworking bees put into it, from immune proteins to the sugar itself.

  • Since ancient times, honey has been used to prevent wounds from getting infected. And

  • these days, we use purified and standardized versions of honey to fight infections in hospitals.

  • Honey has three main tricks for fighting bacteria.

  • The first is all that sugar.

  • Honey is only about 17% water. Most--but not all--of what remains is sugar.

  • The two main types of sugar in honey are glucose and fructose. Like all sugars, glucose and

  • fructose are sticky -- they attract water.

  • Honey is technically a supersaturated solution, meaning it contains more sugar than would

  • normally dissolve at that temperature. That’s why it eventually gets all crystally in the

  • pantry -- over time, the sugar comes out of the solution.

  • Chemically speaking, it’s desperate for water.

  • Water can travel across cell membranes from where there’s a higher concentration of

  • water to where there’s a lower concentration. And there’s a higher concentration of water

  • in a bacterium than in honey.

  • Which means that honey will suck the juices right out of any bacterium -- or mold, or

  • fungus -- that tries to set up shop.

  • Plus, there’s isn’t enough water in honey for any microorganisms to live on. So they

  • die, and the honey doesn’t spoil.

  • The second thing, is that when bees make honey, they throw in an enzyme called glucose oxidase.

  • And bacteria hate glucose oxidase because it produces two different compounds.

  • It converts glucose to gluconic acid and hydrogen peroxide.

  • Gluconic acid is, you guessed it, an acid. It gives honey a pH value of less than 4.

  • That’s about a thousand times more acidic than the neutral pH of 7 that most bacteria

  • need to grow.

  • And hydrogen peroxide is very good at killing cells. It destroys the cell walls of bacteria,

  • which breaks them apart.

  • Glucose oxidase isn’t active in ripe honey--there’s not enough water for it to work properly.

  • It seems to be there to keep the honey from spoiling while the bees are drying it out.

  • But if you dilute honey, the glucose oxidase will switch back on and make gluconic acid

  • again.

  • The final thing bees do to make honey antibacterial? They put antibiotics in it.

  • Some types of honey contain a protein called bee defensin-1, which is exactly what it sounds

  • like.

  • Bee defensin-1 defends bees. It’s part of their immune system and protects them from

  • certain bacteria, including ones that could cause nasty diseases inside the hive.

  • It’s produced in a gland that bees use to make honey, so it makes sense that some of

  • it would make it into the finished product. And while scientists aren’t sure how much

  • of the protein is really in honey, it sort of makes sense that bees would use it to protect

  • their food.

  • Another antibacterial compound sometimes found in honey is methylglyoxal.

  • Methylglyoxal is a small organic molecule that forms in honey from a compound in the

  • nectar of certain flowers.

  • There’s an especially large amount of methylglyoxal in manuka honey, a honey made from a New Zealand

  • flower.

  • This honey is so good at killing bacteria that it’s actually used in hospitals.

  • There’s one bacterium that has honey’s number--but only sort of.

  • It’s the type of bacteria that that causes botulism.

  • The bacteria start out as spores, which are very hard to kill.

  • Theyre already dried out, so honey’s water-sucking properties don’t kill them,

  • and because the spores aren’t growing, they aren’t affected by the acidity or the antibiotic

  • compounds.

  • The really dangerous part of the bacteria is the botulinum toxin they produce when they

  • grow into mature bacteria. Less than a hundred nanograms -- that’s billionths of a gram

  • -- is enough to kill an adult.

  • About 10% of honeys have some botulinum spores in them. But since the spores in honey aren’t

  • growing and making toxin, theyre harmless to healthy adults. Our immune systems intercept

  • the spores before they can start growing inside of us.

  • But the immune systems of infants aren’t always able to kill those spores before they

  • start growing. So, in rare cases, the bacteria can germinate and start producing toxin.

  • That’s why it’s not safe to give honey to infants under one year old, but the rest

  • of us don’t need to worry about it.

  • So the next time youre looking for something sweet, go ahead -- eat some of bacteria’s

  • worst enemy.

  • Thanks for watching this episode of SciShow, which was brought to you by our patrons on

  • Patreon. Thank you, so much, to all of those people. If you want to be one of those people

  • you can go to And if you just want to keep getting smarter with

  • us, don’t forget to go to and subscribe!

Honey. Youve met honey. It’s that sticky, sweet stuff.


單字即點即查 點擊單字可以查詢單字解釋

B2 中高級 美國腔

蜂蜜:細菌的最大敵人蜂蜜:細菌的最大敵人 (Honey: Bacteria's Worst Enemy)

  • 187 22
    g2 發佈於 2021 年 01 月 14 日