May 23, 1998Garlic's benefits: It's all in the preparation
When David D. Ku learned his mother-in-law would be visiting from Hong Kong, a few years back, he stocked up on garlic. To cope with a long-standing sinus condition, the woman "religiously" caps each evening's meal with a minced clove of garlic, he says.
A pharmacologist at the University of Alabama, Ku didn't have a clue why the garlic might help her. "Wanting to be the good son-in-law," however, one evening he started chopping the garlic before dinner. Ku had reasoned that by cutting it before everyone sat down to eat, nobody would have to duck out on the after-dinner tales to prepare her therapeutic tidbit.
Unfortunately, Ku's gesture backfired, because his mother-in-law refused to eat what he'd minced. Surely, she scolded, he must know that garlic was ineffective unless it was chopped just prior to eating.
Well, Ku didn't know that. Nor could he imagine what difference some 30 or 40 minutes might make.
"But now I understand," he reported at the Federation of American Societies of Experimental Biology (FASEB) annual meeting last month in San Francisco. He and another research group described work demonstrating that how the pungent cloves are prepared can prove pivotal to garlic's chemistry-and pharmacology.
The enzyme trigger
The raw cloves contain a sulfur-based compound that can be chemically converted to compounds with druglike properties. However, that initial compound, alliin, is not transformed into the pharmacologically active chemicals unless it makes contact with a critical enzyme that develops elsewhere in the cloves.
Although the plant segregates alliin and the enzyme into different cellular compartments, cooks break down those natural barriers whenever they chop or mash the cloves. Immediately, the enzyme begins converting alliin into allicin, one of the pungent compounds that gives garlic its characteristic aroma. Though short-lived, allicin is pivotal, Ku and others find. It's the first in a cascade of compounds that garlic processing can unleash.
Ku and a team at Pennsylvania State University reported data indicating that if allicin is never produced-or if commercial processing, such as deodorizing the garlic, somehow removes it-this food may lose all or most of its potential therapeutic benefits.
All garlic pills are not alike
Despite his mother-in-law's medicinal use of garlic, Ku only began looking into its biological effects when a patient reported breathing much better after taking garlic. As a result of his liver cirrhosis, the man in question had developed hepatic pulmonary syndrome. It left him so short of breath that the man couldn't walk even a few steps without the use of a respirator-until he began taking a daily pill containing 500 milligrams of garlic.
"Now, even though the liver disease hasn't gotten better," Ku says, "the man can walk around the block." His physicians asked Ku, a pharmacologist studying cardiovascular drugs, "Why is the garlic helping?"
Because people with the syndrome experience localized high blood pressure within the lung's arteries, a condition known as pulmonary hypertension, Ku decided to test the ability of garlic to relax the pulmonary arteries. To do this, he suspended segments of these vessels-obtained from the lungs of a rat-in a water bath, then added a compound to the water that caused the vessel tissue to constrict slightly. Afterward, he added any of various over-the-counter garlic preparations to the water and measured the degree to which they further constricted or relaxed the pieces of artery.
Among the nine types of odor-free garlic pills that he tested, only a few induced significant relaxation of the vessels. Those containing the most allicin caused the vessels to relax most. For instance, one product with 12.5 milligrams of allicin per gram relaxed the vessels to just 20 percent of their pre-test constriction. But two of the pills containing no allicin left the arteries at 80 to 97 percent of the original constriction.
"I don't think that it's the allicin, per se, that's so important," he now concludes. "It's just that without allicin, you risk losing access to all of those other chemicals [that the body produces from it]."
In further tests to tease out how the garlic worked, Ku again exposed arterial vessel segments to the commercial preparations. This time, he had altered some of the exposed vessel segments so that they could no longer produce nitric oxide. Nitric oxide is a chemical that vessel walls produce to trigger arterial relaxation.
The arterial segments that were unable to make nitric oxide only responded to the garlic 30 percent as well as did those arteries with an intact nitric-oxide-production system. Ku now suspects that up to 70 percent of the garlic effect is due to some triggering of nitric oxide production in cells lining the interior of exposed arteries.
Chop first, heat later
Researchers at Pennsylvania State University have been studying garlic's potential health benefits for more than a decade. "And whenever I make presentations on garlic compounds, people invariably ask about home preparation techniques," observes John A. Milner, the Penn State team's leader. "Everyone wants to know what happens to those compounds when they cook garlic?"
At last year's FASEB meeting, his group reported data from a trio of studies showing garlic's promise against various cancers (Cancers do not savor garlic). Though the active agents-a pair of sulfur-based allicin derivatives known as SAC (S-allyl cysteine) and DADS (diallyl disulfide)-tend to withstand cooking, Milner wasn't sure about whether cooking garlic would short-circuit their production. So, he and Kun Song, a graduate student, decided to put raw cloves of garlic into a microwave oven and irradiate them on high for 1 minute.
The heated cloves looked no different than when they went into the oven: Neither their color nor firmness had changed. However, Milner says that microwaving inactivated allicinase, the allicin-producing enzyme. "We're not talking about a 10 percent reduction in the enzyme's activity," he told SCIENCE NEWS ONLINE. "It's no longer effective. Period."
Nor is there reason to believe that other types of heating would prove any kinder to the enzyme, Milner says. This means his family's garlic-rich recipes may need some tinkering. "I'm married to an Italian," he explains. "When my wife begins crushing that garlic, it goes right into hot oil"-well before the allicin has time to launch the chemical cascade that ultimately produces SAC and DADS. "And when we make garlic butter," he says, "we put the whole bulb [of garlic] into the oven. We don't crush it first. So I'm 99.9 percent sure that the enzyme activity will be destroyed here too."
Because it doesn't take long-perhaps 10 or 15 minutes-"to get maximum formation of these anticancer agents [SAC and DADS]," he now suggests that cooks consider employing a little patience when recipes call for garlic. "Crush, nick or chop the cloves as you normally do-then let them sit for a few minutes," he recommends.
These studies are part of a new wave demonstrating the extent to which preparation techniques can make all the difference in whether comestibles qualify as nutraceuticals-therapeutic foods.
For example, he notes, tomatoes' pharmacological advantages appear to improve with heating, which renders lycopene-a pigment with anticancer properties-more biologically available. With garlic's value for fighting pulmonary hypertension and cancer, immediate cooking can have the opposite effect.
The lesson in both findings: Take your time in the kitchen. Your mental and physical health may both stand to benefit. For asthma and other ailments, though, the recipe may be different.
Related Reading
Raloff, J. 1998. . Science News Online (March 14). Raloff, J. 1998. Hot climates spawn hot cuisines (with recipe).
_____. 1997. Looking for lycopene? Tomatoes are okay, but . . . Science News Online (July 19).
_____. 1997. Cancers do not savor garlic (with recipes). Science News Online (Apr. 19).
_____. 1997. Aged garlic may slow prostate cancer. Science News 151 (Apr. 19):239.
_____. 1997. The rise of nutraceuticals. Science News Online (Feb. 15).
Sources
Garlic Information Center
New York Hospital-Cornell University Medical Center
515 E. 71st Street, S 904
New York, NY 10021
Phone: 800-330-5922
David D. Ku
Department of Pharmacology and Toxicology
University of Alabama
Volker Hall G133D
Birmingham, AL 35294-0019
david.ku@ccc.uab.edu
John A. Milner
Department of Nutrition
126 Henderson Building South
Pennsylvania State University
University Park, PA 16802
jam14@psu.edu
This week's Food for Thought has been prepared by
Janet Raloff, senior editor of Science News.