Do milk, honey, and other similar animal products contain significant amounts of DNA?
November 8, 2011 10:01 AM   Subscribe

Okay - I admit I didn't pay as much attention in biology class as I should have. Can someone tell me whether or not animal products such as milk and honey contain significant amounts of DNA? I have a friend who thinks people who talk about eating food that's "free of chemicals" are hysterical, because of course all food is made up of chemicals. But she takes it a step farther and asks if they've tried DNA-free food as well, which brings me to my point. I suggested things like milk and honey, which are secreted by animals, might by considered DNA-free. Her reaction was shock and dismay that I was ignorant of the (to her) common knowledge that those things do, in fact, contain DNA. I mean, I'll buy that maybe they contain some stray particles of DNA - like (I believe) our saliva does, but are they, or are they not, made of DNA?
posted by Death by Ugabooga to Science & Nature (30 answers total) 6 users marked this as a favorite
 
Honey has pollen in it, which has DNA. Milk has lots of cells in it, bacteria, white blood cells and so forth.

All natural food has DNA. Chemicals like salt wouldn't. Really pure sugar wouldn't have any. But almost everything else would.
posted by empath at 10:07 AM on November 8, 2011 [3 favorites]


Yes, there is quite a bit of cellular DNA in milk, both from bacteria and dead epithelial and other cells that were shed from the animal that was milked. Don't know anything about honey. Gross detail, there are quite a few dead human cells in, ahem, boogers as well (100,000 to 1,000,000 per ml), in addition to bacterial cells, and it is not difficult to extract their DNA.
posted by halogen at 10:07 AM on November 8, 2011


I don't understand your question. There's no such thing as "DNA-free food."

Some ingredients used in food (salt, alcohol) have no DNA. But all plant, animal, and fungal matter contains DNA.
posted by dfriedman at 10:09 AM on November 8, 2011 [5 favorites]


Actually, fats and oils wouldn't have very much DNA depending on how processed they are. Really filtered juice probably wouldn't have very much DNA, either.
posted by empath at 10:10 AM on November 8, 2011


Cells (except, for example, red blood cells) contain DNA. Everything alive is made out of cells. Anything you eat that is or was alive (which is most things, I'd hope) is made out of cells, which contain DNA.

I don't like to buy into food hype, but your friend is either not too bright or else deliberately misunderstanding the point being made when people talk about "chemical-free" food - they mean artificial, added chemicals, like pesticides or fungicides or growth hormone or what have you; everything on earth is made out of some kind of chemical.
posted by krakenattack at 10:11 AM on November 8, 2011 [9 favorites]


Nothing is "made" of DNA -- DNA is something that is inside cells. Almost all cells (not cells that don't have a nucleus, such as red blood cells, but basically all other cells). So every single cell of you, or of a plant, or of a cow, contains DNA. So if any part of the animal or plant or fungus or whatever makes it into the food (with milk, for example, there is, as empath points out, at least white blood cells and bacteria in milk), you're eating DNA.
posted by brainmouse at 10:12 AM on November 8, 2011 [1 favorite]


I'll buy that maybe they contain some stray particles of DNA - like (I believe) our saliva does, but are they, or are they not, made of DNA?

I should point out, btw, that even a steak or a potato isn't 'made out of DNA'. DNA is a tiny fraction of the material in any cell.
posted by empath at 10:14 AM on November 8, 2011 [5 favorites]


Almost all eukaryotic cells have DNA in them. Milk and honey are made up of eukaryotic cells.
posted by ellF at 10:16 AM on November 8, 2011 [1 favorite]


Milk and honey are made up of eukaryotic cells.

They *contain* eukaryotic (and prokaryotic actually) cells but they aren't "made up of" them. Both milk and honey are primarily extra-cellular secretions.

But yeah, you could totally genotype the cow the milk came from or the flowers used to make the honey just based on the DNA in there (assuming you got all the other technical details worked out).
posted by shelleycat at 10:22 AM on November 8, 2011 [2 favorites]


To be clearer, all plant and animal cells contain DNA. It's a nucleic acid, which is a type of molecule.

The hierarchy goes like this: atom --> molecule --> organelle --> cell --> tissue --> and so forth. Each level is made up of groups of the previous level. (There are further hierarchical breakdowns within these levels.)

(See Wikipedia's succinct breakdown of biological organization.)
posted by desuetude at 10:29 AM on November 8, 2011


Sure, there are DNA-free (or mostly DNA-free) foods: soft drinks, many candies (boiled sweets, gummy bears, etc...). I wouldn't be surprised is some fruit roll-up products are DNA-free as well.

All of the DNA-free foods share one common feature: they are artificially-produced, highly processed, filtered, perhaps even synthesized from base materials, usually on an industrial scale.

Anything resembling natural food will likely contain at lest traces of DNA from starting organisms.
posted by bonehead at 10:34 AM on November 8, 2011 [3 favorites]


I believe DNA is large enough to scatter light, making liquids cloudy. So clear liquids, and things you can dissolve to make clear liquids, do not contain significant amounts of DNA.

So refined sugar, filtered juice, filtered beer, distilled spirits, & HFCS all fit this.

Of course "doesn't have significant amounts of DNA" doesn't really mean "truly sterile".
posted by aubilenon at 10:35 AM on November 8, 2011 [1 favorite]


I think the most misleading biology phrase of all time is that "everything alive is made out of cells". A better way of phrasing it might be "every part of everything living is made by cells". For example, the human body isn't a big mass of cells -- large chunks of it are mainly proteins. For example, connective tissue is made up of proteins secreted by cells, rather than cells themselves.

Milk is a secretion, i.e. it's a protein-water mix secreted from cells, not cells themselves. As others have pointed out, even though 'pure' milk would thus not contain any DNA, in reality there are bits of cells shed into it, which do contain DNA.

Honey, likewise, is a secretion, but one that contains lots of pollen, which are essentially flower sperm, which do have DNA.

So, the answer to your question depends on what you mean by "significant". Is it enough to detect? Definitely. Is it a large minority of what you're consuming? No. Off the cuff, I'd be surprised if DNA made up 1% of milk or honey by weight. DNA is very very small, so it would take a lot of it to make any significant fraction of what you're consuming.

Of course, I was reading just yesterday that a majority of honey bought in the US has had all pollen extracted. In that case, it's DNA-free.
posted by zug at 10:36 AM on November 8, 2011 [4 favorites]


Is your friend just being snarky? It's pretty obvious(to me, at least) that when people say they want to eat food "free of chemicals" they really mean unnecessary added chemicals/pesticides/etc. Maybe she was being sarcastic with the DNA-free food comment.
posted by fromageball at 10:36 AM on November 8, 2011 [2 favorites]


I guess a question to ask would be what would be considered "significant?"
posted by zomg at 10:45 AM on November 8, 2011


> I think the most misleading biology phrase of all time is that "everything alive is made out of cells".

What a stupid mistake on my behalf - yes, zug and shelleycat are both correct. Milk and honey, assuming you're talking natural sources of it, will contain DNA. They will not be "made up of" eukaryotic cells, since they're largely secretory proteins.

DNA itself would not be large enough to scatter light as seen by the naked eye, as far as I understand it -- an entire skin cell is about ~30μm, and DNA is smaller (albeit coiled) than the nucleus inside of it.
posted by ellF at 10:49 AM on November 8, 2011


DNA itself would not be large enough to scatter light as seen by the naked eye, as far as I understand it -- an entire skin cell is about ~30μm, and DNA is smaller (albeit coiled) than the nucleus inside of it.

Back when I worked in a lab, I could tell when I'd extracted a lot of DNA into a tube vs. when I had a low yield by eye. Cloudy minipreps were good minipreps.
posted by deludingmyself at 10:51 AM on November 8, 2011


All fungi, viral particles, and bacteria (which are pretty much omnipresent) also contain DNA. Most sterilization processes using heat kill or disrupt the structure of these microorganisms but it doesn't break up their DNA, so anything that has ever been exposed to air likely has some bacterial DNA in it. Treating with strong peroxide or bleach will chemically destroy DNA, but would also ruin most foods. Most filtration/purification procedures cannot remove DNA, as some DNA will be randomly broken up during handling of the raw cells. These fragments of different molecular weights will contaminate whatever end product is made (e.g. crushing an apple into juice will almost certainly leak some DNA into the juice). Likely the cheapest way to get rid of the DNA would be to add DNA-destroying enzymes to the end product, but again this would never be done in practice due to cost.

Also note that your friend is continually digesting all of the dead DNA-containing cells sloughed off from her cheek linings, esophagus, and nasal secretions.

You might be able to contrive a DNA-free diet by eating only lab grade purified chemicals, but lunch would cost $1000 and consist of a pile of sugar and amino acids. Perhaps distilled liquor might also be nearly DNA free.

Your friend doesn't know what she's talking about.
posted by benzenedream at 10:53 AM on November 8, 2011


(Which was part of a series of steps to concentrate DNA, admittedly, but as long as we're doing scientific beanplating... yes, you can sometimes tell visually if a solution has a lot of DNA in it.)
posted by deludingmyself at 10:53 AM on November 8, 2011


There's no such thing as "DNA-free food."

Depending on the extraction procedure, some protein preparations may not have much DNA. For instance, casein (a protein) will readily come out of solution if milk is acidified, presumably leaving most nucleic acids and stray cells behind.
posted by en forme de poire at 10:59 AM on November 8, 2011


Crystallized sugar is another example of a not-too-weird food that contains no DNA (since it wouldn't crystallize), I think.
posted by miyabo at 11:02 AM on November 8, 2011


Seitan might be another one: it's wheat gluten, which is what remains of wheat flour after the water-soluble parts have been washed away. DNA is much more water-soluble than protein aggregates (the gluten part) so I'd expect seitan to have very low nucleic acid concentrations relative to, say, meat.
posted by en forme de poire at 11:05 AM on November 8, 2011


Of course, I was reading just yesterday that a majority of honey bought in the US has had all pollen extracted. In that case, it's DNA-free.

Honey also contains bee spit, so there would still be some bee DNA in there. Even without the spit actually, it's likely that bee cells slough off and end up in the honey at various stages. It would be very very very (very!) small amounts of course.
posted by shelleycat at 11:13 AM on November 8, 2011


Put it this way. With every breath you take you are inhaling thousands of bacteria, pollen spores and specks of dust made from human skin. All of which contains DNA.

The idea of DNA-free food is ludicrous.
posted by TheOtherGuy at 11:58 AM on November 8, 2011 [3 favorites]


Is your friend just being snarky? It's pretty obvious(to me, at least) that when people say they want to eat food "free of chemicals" they really mean unnecessary added chemicals/pesticides/etc.

It sounds like that's her point - drawing attention to how such a broad imaginary/ideological distinction is not useful and in some case harmful, compared to a nuanced evaluation that can allow for the concept that not everything is necessarily always terrible.

It sounds like she's saying "'Chemicals are bad m'kay' is a rule of thumb, not gospel."
posted by -harlequin- at 12:00 PM on November 8, 2011 [5 favorites]


I'm having trouble understanding why she would even bring up the concept of DNA-free foods... what would that even mean? Does she mean non-genetically modified foods? Because while you could argue that all domesticated plants and animals are genetically modified to some extent (through selective breeding), wild-caught foods like, say, a lot of fish, are not. Bees, I don't know about.
posted by mskyle at 12:24 PM on November 8, 2011


I'm having trouble understanding why she would even bring up the concept of DNA-free foods... what would that even mean?

It means the same as the concept of chemical-free foods. She is using DNA-free to make an analogy to back her point that "chemcial-free" isn't a useful way to think about food.

Or at least that was my interpretation.
posted by -harlequin- at 12:45 PM on November 8, 2011 [4 favorites]


Your friend sounds like a smarmy twat I know who likes to say 'Of course it's organic - it contains carbon! Haw haw haw!"
posted by obiwanwasabi at 3:12 AM on November 9, 2011 [1 favorite]


Sorry - I guess I made the assumption that people would realize my friend was being facetious in order to make fun of people who panic at the mention of "chemicals". And no - she doesn't believe there is DNA-free food; that was me, trying to poke holes in her snarkiness. But it's good to see it's not as cut-and-dried as I thought it might be. It's always fun to poke the hive with a stick and see what flies out. ;-)

Even when it comes to "organically grown" food, while I know what people, in general, mean by that phrase (I do the whole "Buy Local" thing, including farmers markets, and I grow some of my own food), it's a pretty broad brush. People who say "Of course it's organic - it contains carbon" might not be too far off the mark. I mean - even when I grow my own vegetables using ladybugs for pest-control and composted horse manure for fertilizer, what's to say that the horse wasn't being given chemical treatments of some kind that ended up in the poop? I'm well aware that I'm splitting hairs, but that's sort of the point. agreed-upon generalizations often lead to unintended consequences.

Anyway, thanks for all the interesting answers. At least I can tell my friend that yes, there _probably_ is something that could be called "food" that is DNA-free, right?
posted by Death by Ugabooga at 6:46 AM on November 9, 2011


This is a great question, the ways people reasoned out their answers are fascinating. Minus the expected one or two commenters who are focused on why you shouldn't have asked the question in the first place :P
posted by variella at 11:21 AM on November 9, 2011 [1 favorite]


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