4. More stable products are formed when allicin and its "cousins"
stand at room temperature for a few hours or days. A good example of this
situation is macerate of garlic, a product formed when garlic is chopped
("macerated") with salad oil or other edible oils. Macerate of
garlic is a rich source of "naturally-formed" garlic-derived compounds
having the scientific names ajoene, methyl ajoene, and dithiins. These products
are stable enough to be stored at room temperature for more than a year,
for example when dissolved in an edible oil.
5. Materials prepared by heating garlic in boiling water and condensing
(collecting) the steam as it becomes a vapor, a technique known as steam
distillation. The product is termed the distilled oil of garlic. The scientific
name for the major component of distilled oil of garlic is diallyl disulfide.
It has a strong, slightly medicinal, "artificial" smell of garlic.
Distilled garlic oil is used as a food flavoring agent.
In summary, when we cut or crush fresh garlic, we release an enzyme called
allinase which rapidly converts odorless alliin to allicin, the latter having
the typical odor and taste of fresh garlic. Allicin is unstable and rapidly
reverts to ajoene (pronounced ah-hoe-ene) and dithiins (pronounced di-thigh-eins)
in the presence of edible oils (e.g. macerates) or to diallyl disulfide
on standing or heating in water. I explain more about the sulfur compounds
in garlic in my article in "Scientific American (March l985, pages
Passwater: Are you saying that it is not the alliin and allicin themselves
that are important, but compounds that are formed from these compounds,
either in the body or by certain types of cooking?
Block: If by "important" you mean "having a positive health
benefit" the answer to that question is still actively being sought
by researchers. There seem to be health benefits associated with most of
the sulfur-rich components of garlic following its normal use in cooking
and consumption. For example, I've already mentioned that ajoene and dithiins
are naturally formed when garlic is macerated with various edible food oils.
Passwater: You mentioned "ajoenes". I had seen several recent
articles describing their benefits, but I was not familiar with them. In
fact, I didn't even remember ever studying "ajoenes," and they
didn't seem to fit into standard terminology, so I had to check the Merck
Index for details.
Block: Don't feel too bad. I discovered them in 1984 and named them in honor
of my collaborators in this research from Venezuela. "Ajo" is
the Spanish word for garlic. I'm quite proud that ajoene has been included
in the latest edition of the Merck Index. By the way, alliin and allicin
are derived from the botanical Latin name for garlic, Allium sativum
Passwater: Okay, I feel better! How many papers have been published about
ajoenes since you discovered and named them?
Block: I have seen more than a dozen scientific papers from laboratories
around the world dealing with medical benefits of ajoene. I have also seen
quite a few papers dealing with ajoene analysis and occurrence. These latter
papers indicate that macerated garlic is the only form of garlic where significant
quantities of ajoenes and dithiins have ever been detected.
Passwater: What health benefits do ajoenes provide?
Block: Well as I said, ajoenes and dithiins are among the most active compounds
formed from fresh garlic. Ajoenes have been shown to: possess antithrombotic
(anticlotting) activity in human platelet suspensions [l-8]; possess antitumor
activity ; display significant antifungal activity, inhibiting the growth
of Aspergillus niger , Candida albicans , Paracoccidioides-Brasiliensis ,
and Fusarium species [10-12]; inactivate human gastric lipase, a
sulfhydryl enzyme involved in the digestion and adsorption of dietary fats
; function as antioxidants by inhibiting the interactions of leukocytes
which mediate release of superoxide anion .
In one interesting study, administration of ajoene to dogs under extracorporeal
circulation (as used in open heart surgery) prevents the thrombocytopenia
induced by contact of blood with artificial surfaces. In this same study,
ajoene showed excellent activity in preventing loss of platelets and in
increasing rate of restoration of platelet clotting activity [1-5].
Exciting advances have also been reported for dithiins as well. For example,
A U. S. patent was recently awarded to a scientist at the Los Alamos National
Laboratory for the invention of a copolymer involving the same dithiin formed
from garlic for an "antithrombogenic and antibiotic composition for
use as a coating for artificial prostheses and implants which remain in
contact with blood" . Thus, basic research on garlic chemistry
has led to the development of a new type of plastic in which a stable garlic-derived
anticlotting and antibiotic agent provides unique properties of potential
use in heart valves, artificial blood vessels and other implant devices.
Passwater: Are the ajoenes and dithiins the only garlic components that
are actively being studied for possible protection against heart disease?
Block: As far as I am aware.
Passwater: Now, when we are talking about the health benefits from garlic
and garlic's sulfur-containing compounds, is it your view that we are not
talking about sulfur-compound nutriture, such as with the sulfur-containing
amino acids cysteine or methionine, but with the "herbal" properties
of garlic which are health benefits beyond those of nutrients?
Block: I would like to respond with a qualified yes. In addition to those
compounds formed from garlic such as allicin and ajoene, there are various
cysteine derivatives from garlic related to alliin containing allyl groups
attached to cysteine sulfur which may also have health benefits. However
to be of value, these allylic compounds wouLd have to be present in significant
quantities in what is consumed.
Passwater: You mentioned that we get the most beneficial compounds from
cooked garlic or garlic prepared with edible oils and not directly from
raw garlic -- what about garlic supplements?
Block: My basic research through the years has focused on fresh garlic and
compounds such as ajoene directly derived from fresh garlic and on the biological
activity of pure samples of ajoene and related compounds. I myself have
not been involved in the preparation or evaluation of different commercial
garlic supplements so I can only answer your question based on what I have
read in the open literature.
There are quite a variety of different garlic products on the market. There
is certainly a need for independent testing and evaluation of these different
products and careful examination of their claims. Some products talk about
allicin content, allicin potential or allicin yield. Since there is no way
to stabilize allicin itself, any claims concerning actual allicin
content in a product cannot be correct. Intact garlic cloves themselves
do not contain allicin either, although upon cutting or crushing under ordinary
circumstances allicin is formed.
Thus one can talk about the allicin potential or allicin yield from garlic
cloves. If garlic cloves are frozen in dry ice, pulverized with acetone
in the absence of water, and the powder is then briefly heated with alcohol,
not a trace of allicin can be detected following addition of water because
these conditions destroy or "denature" the allinase enzyme which
is required for allicin production.
These very conditions were employed 50 years ago by Chester Cavallito, the
discoverer of allicin, to demonstrate that an active enzyme is a requirement
for allicin formation. In this particular case the allicin potential is
unfulfilled because the enzyme has been denatured.
With a garlic supplement claiming allicin potential, I would assume one
is talking about some type of preparation in which water has been removed
from garlic and the resulting product then pulverized and encapsulated.
I further assume that when the contents of the capsule are exposed to water,
allicin is produced. The critical question is whether or not the required
enzyme is destroyed during the actual digestive process at the time when
the coating of the capsule dissolves. Just as hot alcohol can denature the
sensitive allinase enzyme so too can the strong acid present in our stomach.
While allicin itself is highly unstable and can only be produced when both
the precursor alliin and the enzyme allinase are present under non-denaturing
conditions, the situation with ajoene-containing products such as garlic
macerates is somewhat different. Since ajoene and dithiins are already present
in the macerate, no sensitive enzyme is required. To the best of my knowledge
the only commercial products which have been unequivocally shown to contain
significant quantities of ajoene and dithiins are macerates of garlic.
Passwater: Is there a direct relationship between the amount of beneficial
garlic compounds in your system and being able to detect their presence
on your breath.
Block: Garlic breath has been a matter of concern since garlic was first
cultivated and used as a seasoning thousands of years ago. The fact is that
the human nose is extraordinarily sensitive to the very types of sulfur
compounds formed when we digest garlic and its derived products such as
allicin, ajoene, and diallyl disulfide. When the sulfur compounds are digested
they are broken down into simpler sulfur compounds, a portion of which enters
the bloodstream and is then exhaled from the lungs or eliminated through
our pores when we sweat. Since the human nose can detect less than one part
of these sulfur compounds in one billion parts of exhaled air , it
doesn't require much garlic or garlic compounds to give us garlic breath.
It has even been reported that babies born to mothers who consumed garlic
prior to giving birth have garlic breath. Not that the babies complain!
In fact other studies suggest that babies actually prefer slightly garlicky
mother's milk. If we can assume that it is the sulfur compounds of garlic
that are primarily responsible for its health benefit, then it seems illogical
to expect benefit from a product where not a trace of garlic breath can
be detected after consumption.
Passwater: What do you see happening with garlic research? What is your
next garlic or sulfur chemistry problem to solve?
Block: At the present time the use of garlic in cooking and, in processed
form, by the food industry constitutes the largest market for the "stinking
rose." There is still a need for better analytical methods to accurately
and rapidly measure the amounts of allicin and related compounds in freshly
cut garlic and to understand the fate of garlic flavorants under a variety
of processing or culinary conditions. At the same time we need to better
understand the biological properties of the various types of sulfur compounds
formed from garlic and, in particular, to rigorously establish the effect
of these different compounds on human health and in the prevention of disease.
Since there is great interest in garlic and its health benefits I believe
we will be seeing significant and exciting progress in all of these areas
during the next few years.