Onions and garlic have evolved chemical weapons to protect themselves from predation and disease. In his book Garlic and Other Alliums: The Lore and the Science, chemist Eric Block describes that intricate chemistry, and writes of alliums in kitchens, medicine cabinets and opera houses.
Copyright © 2010 National Public Radio®. For personal, noncommercial use only. See Terms of Use. For other uses, prior permission required.IRA FLATOW, host:
You're listening to SCIENCE FRIDAY from NPR. I'm Ira Flatow. If you're cooking, you're cooking out this holiday weekend, barbecuing maybe, perhaps throwing some onions or leeks on a skewer, marinating your meat in garlic - well, my next guest has spent nearly 40 years investigating garlic and onions, not just in the kitchen but in the chemistry lab.
He has studied just about and he knows just about, I'll bet, all there is to know about members of the genus allium: garlic, onions, leeks, chives, other kinds of good stuff like that. And he has a new book out. It's called "Garlic and Other Alliums: The Lore and the Science," and it's sort of an ode to his love story with the alliums. He's here with us.
Eric Block is the author of "Garlic and Other Alliums: The Lore and the Science." He's also a distinguished professor in the Department of Chemistry at the University at Albany, part of the State University of New York. He's here with us in our New York studios. Welcome to SCIENCE FRIDAY, Dr. Block.
Dr. ERIC BLOCK (University of Albany): Welcome, Ira thank you very much.
FLATOW: Every - they used to say (unintelligible) everything you've ever wanted to know about garlic and other alliums is in this book. How did you get interested in this? It's not something you'd see every day.
Dr. BLOCK: Well, as so many things happen in life, particularly in the sciences, it's serendipity. And I had worked at Harvard with a Nobel Laureate by the name of EJ Corey, who was working on a molecule called dimethyl sulfoxide. Dimethyl sulfoxide is a sulfur-containing molecule, very simple and very interesting chemistry, and I decided as a fresh faculty member at the University of Missouri, St. Louis, where I began my academic career, to do something different by not too different.
So I decided to do what chemists do, and that is make a slight modification in the structure of a well-studied compound and see what happened. And the slight modification that I did was to add an element, an atom of sulfur. So instead of having one sulfur, it had two sulfurs, and as I began to study this molecule, I found more and more interesting chemistry, but I soon discovered that I had stumbled in quite accidentally to the primary compound that gives garlic its flavor.
FLATOW: Wow.
Dr. BLOCK: So it was purely serendipity.
FLATOW: Yeah, but you went around tasting garlic for the next 40 years.
Dr. BLOCK: Well, smelling of garlic, actually.
(Soundbite of laughter)
FLATOW: It is hard to get off your fingers.
Dr. BLOCK: Particularly if you're in the laboratory and particularly if you have a moustache, as I do, and you touch your hair. Sulfur is actually part of hair, and the sulfur compounds in garlic and onions can actually attach themselves to hair and clothing. So it does go it does travel with you. But what it does is guarantee you a seat on the subway.
FLATOW: 1-800-989-8255 is our number, if you'd like to talk about onions and garlic and leaks. And what other members are there of the allium family?
Dr. BLOCK: Well, one of the things I wanted to point out is that you don't just judge a genus but the few very well-known members. It's actually a wonderful genus of almost 800 species. It's almost as large as the family involving orchids.
But there are a large number of decorative plants, and we call them ornamental alliums. There are also architectural plants in the sense that after the blossoms wither, the structures remain, and they look like giant Christmas tree ornaments. So they're highly desirable in gardens, and there's a tremendous interest in the ornamental alliums. There's worldwide blog sites and websites where people discuss their favorite allium of the day.
FLATOW: Let's talk about some allium questions that we all let's start with our favorite onion. What happens why can you have an onion in front of you, yet when you slice it and dice it, whoa, it releases all that kind of stuff that makes you tear up?
Dr. BLOCK: Well, that's part of what is so much fun about studying the alliums, that the chemistry is absolutely fascinating and it teaches the scientist and the student an awful lot. It turns out that in the intact onion there's not much odor, but as soon as you touch it or crush it or cut it, an enzyme mixes with an odorless(ph) precursor to initiate a cascade of reactions.
There are actually several enzymes involved, and they take this odorless derivative of an amino acid called cysteine, and they turn into something that even Shakespeare referred to. The tears live in an onion that should water the sorrow, was Shakespeare's way of talking about a molecule that my colleagues and I discovered and characterized using some very sophisticated methods of analytical chemistry.
FLATOW: And why does the onion have this? Is it a defensive mechanism built into it?
Dr. BLOCK: Yes, the types of compounds that are found in plants are either those responsible for the nutrition of the plant, or they're secondary to that. So they're called secondary metabolites.
And they're often toxins. They are often compounds that will repel insects or animals that try to bite into it. So everything is, I believe, very Darwinian from the standpoint of the chemistry of plants, a very large number of compounds that we view as either being pleasant smelling or unpleasant smelling.
They're not there for our pleasure. They're there to allow the plant to survive in a very hardscrabble world, a world where there are lots of worms in the ground and animals that would devour something that exists as a bulb and has to survive in the ground.
So if you're living in the ground as a perennial, as the garlic does, you need to defend yourself, and you can't run. Plants can't run. So they stay and fight, and they're wonderful at it.
FLATOW: Well, you know, a lot 1-800-989-8255. All during the spring and the summer, when your grass is growing, we see all this, it sort looks like garlic growing in the grass, but it's what is that?
Dr. BLOCK: Well, that's a very annoying plant. It's a wild onion. For some people it's kind of the first sign of spring. When you go out in the fields and wander through it, and as your pants and shoes crush it, you suddenly get this aroma of onions.
But it's actually faster-growing than grass, so that if you have the wild garlic, the wild onions in your grass, it shoots up. It's kind of ugly. It's a different size, different shape, and a particular problem with the wild garlic is if you're a farmer and you have cows, and if the cows eat the wild garlic, then the cows have garlic in their milk, and that milk is pretty hard to sell.
FLATOW: Actually, I used to clip off the tops and put them in a salad. Actually didn't taste that bad...
Dr. BLOCK: Well, but if you're talking about milk and ice cream, I don't think you want garlic in it.
(Soundbite of laughter)
FLATOW: No. Let's talk about - let's talk about garlic, because garlic in folk medicine has a reputation for lowering your blood pressure, your cholesterol, stuff like that. Is there any real science to back that up?
Dr. BLOCK: Well, actually, the question is a bit broader, because there is a vast number of different remedies that our grandparents have passed down. So really, you have to ask a question about each of those many remedies because each one is different, and whether it's dealing with cancer, whether it's dealing with cholesterol or the ability to trek the Himalayas and not be affected by the lack of oxygen, there are just so many of those remedies that are there.
So each one has to be investigated separately, and my colleagues and I, Christopher Gardner(ph) and Larry Lawson(ph) at Stanford University, actually did a clinical trial in which we compared fresh garlic, a placebo - that is, nothing at all, to two commercial supplements with a lot of a large number of people under rigorously controlled conditions, and the results of this research was that the placebo was the most effective.
So unfortunately, at least in that careful trial, garlic lost out, and we concluded that for people that are moderately hyperlipidemic - that is, have slightly elevated lipid levels, garlic is really no better than eating an M&M.
FLATOW: There you go. Let's go to Absey(ph) in Birmingham, Alabama. Hi, Absey.
ABSEY (Caller): Hi. I just have a quick question. I've noticed that some people seem to have a higher sensitivity to those onion fumes, and I wondered why that might be and if there's a way to decrease your sensitivity, because I have to get a box of tissues every time I chop an onion.
FLATOW: If you chop it under water - there's a remedy. Cut your onions under water?
Dr. BLOCK: Well, again, you have to consider the chemistry of what is involved before you can come up with a remedy. So the molecule that causes tearing is a very small molecule. It's very soluble in water, and being a small molecule, it's relatively easy for it to go into the gas stage.
So what you do is either to cool it down before cutting it, which reduces its volatility, use a kitchen hood to pull the fumes out, or you chop it under water, or anything else that would take a water soluble small molecule out of the air.
But I wouldn't suggest putting a match in your mouth with your teeth... or a piece of bread.
FLATOW: Oh, that old remedy, yeah.
Dr. BLOCK: ...or a piece of bread.
ABSEY: Yeah, I've heard that one before.
Dr. BLOCK: Those are urban legends that are just not true.
ABSEY: Right.
FLATOW: All right, Absey, have a good weekend.
ABSEY: Thanks, you too.
Dr. BLOCK: Thank you.
FLATOW: What about cooking garlic? Is there a right way and a wrong way to cook it?
Dr. BLOCK: Well, I think there are just so many recipes and so many different uses of garlic. One of the things that you need to be cautious of with all the alliums is that if you overheat them, if you cook them under temperatures that are slightly too high, you can get a horrible taste, because you can convert some of the fragile chemicals into bad-tasting chemicals.
So you need to be very cautious about the temperature, and also, if you want to maximize the effectiveness of a simple clove, you need to chop it very thoroughly, because the taste only originates when the enzyme mixes very thoroughly with the precursor.
FLATOW: Mm-hmm.
Dr. BLOCK: So if you just slice it once or twice, you're going to be wasting all those valuable molecules that are just not going to be converted into the delicious molecule called allicin, which is the essence of very fresh garlic.
FLATOW: So when they tell you to smack with a knife blade edge, the side of the knife, crush it that way.
Dr. BLOCK: Yes. Yes. That is one of the techniques that is...
(Soundbite of laughter)
FLATOW: Some of those fun techniques. I don't want that garlic crusher. That's too easy.
Dr. BLOCK: Right, right.
FLATOW: 1-800-989-8255. Joel(ph) in Little Rock. Hi, Joel.
JOEL (Caller): Hi, Ira. How you doing?
FLATOW: Hi there.
JOEL: Hey, listen. I grew up in Ozarks and one of the biggest remedies my mother used - still use it - was whenever we got sick, we took a little bit of garlic. And so, first of all, I wonder is there any value to that? Second of all, I was reading in an herbal book the other day, that they - the writer said that you have to chew it in order for it to give you any value. And you know what that does to your breath. So I just wondered what your guest would have to say about that.
FLATOW: Garlic breath.
Dr. BLOCK: Well, you raised some very interesting points. First of all, there is something called the placebo effect, in which something that your grandmother tells you with a good sense that it's a - it's correct, it will make you feel better. So, some of the home remedies are really more psychological. As far as crushing it, yes, you do need to chop the garlic to release the maximum amount of the molecule called allicin. Now, allicin in the Petri dish is an antibiotic.
But one of the concerns with the garlic as a remedy, is that it actually has to pass through the digestive system where it's broken down pretty much to the major component of bad breath. So you lose the antibiotic once it gets into the body. But in the stomach, it might work. So there are some anecdotes about individuals going across the border to Mexico or other places where the water may have some organisms in it that can cause dysentery. And it's been said that by chewing on garlic you can reduce the risk. In fact, that's in literature from Pliny the Elder in the 1st century, from 2,000 years ago. And that makes sense and it's actually been verified by a colleague at the Weizmann Institute. Allicin is actually a very potent killer of amoeba. And if you chew it and the amoeba are in your stomach before the allicin is denatured, it will work.
As far as the common cold is concern, I don't think the evidence is compelling there. A common cold is not going to be cured just by eating garlic. It might keep other people with colds away from you, which is one of the other uses of garlic. If you don't want to get a cold and you chew a lot of garlic and keep people keep their distance.
FLATOW: 1-800-989-8255 is our number, talking with Eric Block, author of "Garlic and Other Alliums: The Lore and the Science" on SCIENCE FRIDAY from NPR. I'm Ira Flatow.
Is that where the Dracula garlic thing connection came from? Because if you wear all that garlic, people will stay away from you or you eat a lot of it or...
Dr. BLOCK: Well, I think it's more than that. I think that in the Middle Ages when people did not have a very good idea of what caused disease, they felt that because garlic smelled so bad it must be wonderful in keeping away diseases. So people used garlic to ward off whatever caused disease, which were - also included some supernatural creatures that people thought were responsible, the devil and so forth. So...
FLATOW: I get it.
Dr. BLOCK: ...from there it went to Dracula. But there's actually a little bit of irony in that whole story. So, of course, you repel a vampire by the odor. But, of course, what does a vampire do? A vampire sucks blood. And so a vampire wants its victims to have blood that doesn't clot. Well, garlic has a natural anticoagulant in it so, aha, the jokes on us, actually. So, actually, the vampires would like nothing better than to nibble on someone whose body is full of anticoagulant.
FLATOW: I want to see that on HBO this season. 1-800-989-8255. You said it was an antibiotic. Could you put it, topically, then, on a cut or something?
Dr. BLOCK: Well, that's a wonderful suggestion. Yes, you could use it but very cautiously, because in my book I have some pictures that are pretty gruesome that are taken from journals of dermatology that show exactly what happens if you try to treat athlete's foot or fungal infections by rubbing cloves of garlic on it. And it will kill the fungus but it also will kill the skin and send you, very quickly, to the hospital, to the emergency room, for a very serious burn which may take weeks to heal.
So don't mess with garlic. It's very potent stuff and one should would be very cautious, especially with children. Never try to treat a child with some home remedy involving garlic, because it can cause a lot of injury to that small problem.
FLATOW: Let me see if I can get a quick call in before the break. Roger(ph) in Ann Arbor. Hi, Roger.
ROGER (Caller): Hi, Ira.
FLATOW: Quickly.
ROGER: I just - I have a slight allergy to garlic, but I love garlic. And so, I'm wondering is there any kind of way I can still eat garlic and yet not have the allergy?
Dr. BLOCK: The answer is probably not. I've heard from so many people who suffer from allergies to alliums. And when you're dealing with a food allergy, you can be tested for it, you can be given samples of it so that your body may develop an immunity, but that has to be done through an allergist. And it's not an easy - it's not a trivial thing. So my sympathy, but I guess you should just avoid garlic and try other foods that you find enjoying.
FLATOW: Could you have another allium besides garlic, that you might not be allergic?
Dr. BLOCK: Yes. Sometimes someone who's allergic to garlic can tolerate onion or leek. But you have to carefully test each of the alliums, small amounts to see if you indeed are allergic to those.
FLATOW: Do you have your favorite?
Dr. BLOCK: Do I have my favorite allium? Well, they're kind of like my children. I think each one is interesting in its own way, and leek and potato soup, and garlic bread, and roasted onions, chives on sour cream. They're all good and I wouldn't want to say one is my favorite. I like them all.
FLATOW: I like them all (unintelligible) also.
(Soundbite of laughter)
FLATOW: Well, we only have 20 minutes to go. That's good. We can go out and get some of that. We're going to take a short break. When we come back, we're going to talk lots more with Eric Block, author of "Garlic and Other Alliums: The Lore and the Science." You can tweet us:
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