I've read that in a couple of places.

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    Please name one of those places. This doesn't make much sense; how would friction destroy a chemical? – BobMcGee Jul 9 '11 at 18:32
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    Not saying that this is the case, but friction causes heat, and heat can alter chemicals, making them less effective. It is not a bad hypothesis to think that friction may alter the chemicals that make up vitamins. see: wiki.answers.com/Q/… – Cos Callis Jul 10 '11 at 4:33
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    @Cos Callis: Chemically speaking, vitamins and proteins are two very different things. That page says: "cooking will alter the vitamins' structures (heat denatures things like enzymes and proteins)" which is like saying that because moderate heat can melt ice it should also melt iron... – nico Jul 10 '11 at 15:00
  • @nico, you miss the point entirely. OP asks if centrifugal juicers destroy vitamins through friction? @BobMcGee says, "That doesn't make much sense...` (as if OP has asked "are vitamins different on Tuesday?") My point was that if heat can alter vitamins it is a plausible hypothesis that friction might also affect vitamins. Others have attempted answer OP's question, my point was more directed at @BobMcGee to say that it is a reasonable question regardless of the answer. – Cos Callis Jul 10 '11 at 18:00
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    @Cos: I understood your point. I am just saying that whoever wrote the text in the link you provided is talking about vitamins and proteins like they were the same thing. – nico Jul 10 '11 at 18:06

There are two explanations usually given for why centrifugal juicers lose some of the nutritional value:

  • frictional heating, supposedly from the higher speed of the moving parts (although it's never clearly explained where this comes into play, maybe from the juice splatting on the container)
  • aeration of the juice (since there's usually more frothing with a centrifugal juicer), which causes the juice to oxidize more and faster.

This page is fairly typical of the explanations.

I'm personally not convinced that either of these is a huge issue, but OTOH I do like the twin-gear masticating juicer we have because it can juice anything and doesn't suffer from those supposed disadvantages of the centrifugal type.

  • I just bought the Hurom Slow Juicer and it's very interesting. Slow squeezing of the items and plenty of juice. It even juices wheatgrass! – user6614 Jul 11 '11 at 1:53
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    @user6614 - I'll bet it crushes the vitamins. <g> – Pete Becker Feb 19 '13 at 12:40

Short answer is no. Vitamins are organic compounds (that is, compounds based on a carbon skeleton) which are pretty small: most of them are formed by 20-30 atoms, not more than that.

Mechanical stress, as well as thermic stress, can indeed interfere with the structure of big organic compounds such as proteins or DNA, which are called macromolecules and are formed by thousands or even millions of atoms connected in complex 3D structures. However, this is not the case for vitamins.

So, in substance, continue to drink your orange juice and you'll be fine!

EDIT: standing what I wrote, it is also interesting to consider that certain vitamins can be enzymatically degraded. This is for instance the case of vitamin C: this article demonstrates how vitamin C degradation could happen when processing broccoli at <60°C, due to the action of an enzyme called vitamin C oxydase. Of course this does not necessarily apply to other vegetables/fruit or to other vitamins.

Personally, I think that the passage of a fruit in a juicer is sufficiently fast that I really doubt there would be enough time for the vitamins to degrade. Would be an interesting experiment to do though.

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