Wednesday, May 17, 2006

Cyanogens in Legumes

Ahh, a break from shovelling. I'd rather be lounging than typing, but I develop such burning questions while I'm shovelling. I remembered a recent post by Eleutheros titled "Leather Britches," and got thinking again about cyanogens in legumes. Being basically lazy, I decided to just toss my questions out here and see if some of you can save me the research. If not, I'll try to find the answers in a week or two . . . after I've got my legumes planted.

Here's my quandary. I've heard that mature seeds of legumes, such as dry beans, should not be eaten raw or undercooked because they contain cyanogenic compounds. A wee bit of browsing the 'Net suggests to me that the problem is probably more complex and less universal than the way I just put it. But if it actually is that simple, then I have lots of questions:
  1. Does sprouting break down these compounds?
  2. Does it matter if a few unsprouted seeds remain in my batch of sprouts?
  3. At what point do these compounds develop? What if I let my peas get a little old and starchy?
  4. Since Eleutheros eats dried green beans, does that mean that the cyanogens develop only as the seeds are allowed to fully mature?
  5. Or does it mean that Eleutheros is tough?
  6. Or does it mean that cyanogens aren't a problem in all legumes, just some?
  7. Or does it just mean that this problem is overstated by overcautious food experts?
I went looking for details about green potatoes a while ago. How green does a potato have to be before I should worry about toxicity? Can I just peel off the green part? I dug through scads of sites warning about the dangers of green potatoes, and then finally found one (sorry, lost the link) that said you'd have to eat something like 200 pounds of green potato in one day to see any negative effects. Humph.


Anonymous said...

This is such a neat post, Laura. It appeals to my interest in plant secondary products and to my hate-love affair with organic chemistry!

Here is a site that lumps cyanogens and other things into "Anti-nutritional factors". For legumes this also includes "trypsin inhibitors", small proteins that inhibit the digestive enzyme trypsin. Presumably this helps protect the seed from being eaten by insects, and is another reason why we typically cook the seeds of legumes (we use trypsin too).

As for the cyanogens, I find that they are sugars with a nitrile group attached, so I suspect they accumulate as the embryo develops. Enzymes called glycosidases degrade them to HCN, hydrogen cyanide, which is how they're toxic. This can happen when the embryo is damaged and probably as the seed germinates.

Some legumes, perhaps the ones that are used for sprouts, probably don't make much in the way of cyanogens. Others do. Best easy way to detect whether your sprouts are making it is to open the covered sprouting jar and sniff for an almond odor that indicates HCN.

As for potatoes - the neat thing there is that the potato tuber is actually a modified stem, rather than the root most people think of them as being. So in the light, the potato begins to behave like a stem, with the skin greening up and beginning to produce the solanin and nasty alkaloids that the plant's stems and leaves make. As you say, the best way to deal with it is just to remove the green skin, and as you also say, the amounts of alkaloids made are pretty small.

arcolaura said...

Thanks Wayne! Lots to chew on there. It hadn't occurred to me that sprouting might actually produce the cyanide, rather than neutralizing it. More questions!

CG said...

I'm pretty sure it would mean that hillbillies eat their mature beans cooked.

Normally, dried beans (including shucky's)are soaked overnight (or brought to a boil, turned off and soaked for 2 hours), then cooked by either boiling until tender (several hours) or pressure cooked at 15# for 30 minutes. A piece of fat salt pork is also traditional as flavoring.

Also consider the millenia people have eaten mature beans.

Which is the same thing I think when they start spouting that charred meat is carcinogenic! LOL!

Anonymous said...

Laura, Laura!

Stop worrying. You are going to cause yourself more harm worrying than eating a barrel full of raw beans and green potatoes!

Wayne took care of the chemistry, no need to go there except to mention that 'cyanogen' means 'cyanide producer' (actually literally 'blue producer')

As for small amounts of cyanide and solanin, the human chemistry has 'chemical channels' specifically there to handle small amounts of things that the person is going to encounter in the normal course of things. There's arsenic in everyone's water, it's there naturally. Likewise tiny amounts of lead, alkyloids, and a host of other things. The human chemistry isn't foolish, it knows those things exist and it has planned for their elimination. For most such things you have to raise the level above a certain toxic amount before there is any effect at all.

As to dried beans (including leather britches), if you undercook them, you wouldn't be eating them anyway because they are quite foul tasting unless they are fully coooked. Small danger of eating too many undercooked beans. Likewise the green peel of a potato tastes very bad and so there's little danger of ingesting solanin in toxic amounts.

If you did manage to eat a sufficient quantity of undercooked beans or green potatoes, you'd likely only do it once. They would upset your digestion quite emphatically.

It would be better to eat whole, fresh, organically grown vegetables. But if all you could get were old, chemical, processed vegetables fromt he grocery store, which would be better, not eating vegetables at all or eating the agribusiness vegetables?

The answer is a far and away, no question about it, eat the canned or frozen vegetables rather than none at all. The benefits of ANY vegetable far, far, far outweighs the drawbacks trace pesticide and loss of nutrition due to processing. The advantage is ten thousand to one at least.

Like that, the benefits of whole beans and whole potatoes (with the skins on) a bazillion to one outweigh the microscopic dangers that you might encounter a significant amount of cynogens. That is, better to crunch down on raw beans than to eat none at all.

And yes I am tough. Tough as an old hickory stump which I grow to resemble more and more.

arcolaura said...

Thanks, CG, Eleu - I'm much enlightened and unburdened. Not that I actually worry all that diligently. I just worry out loud to see what people will say. Sort of like when I used to mumble something like "It's getting dark in here," and the other person present would get up and turn on a light, allowing me to continue my reading uninterrupted. But lately I do try to be a little less lazy and more grateful. So, thanks!