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The Chemistry of Garlic Health Benefits
© Interview With Professor Eric Block Ph.D. Interviewed By Richard A. Passwater Ph.D.
I have been sharing my interest in selenium- and sulfur-containing nutrients
for some time. Recently, I shared with you a conversation with selenium
expert, Professor Gerhard Schrauzer, Ph.D. Now, I thought you would like
to share a recent conversation I had with sulfur-chemistry expert, Professor
Eric Block, Ph.D.
Dr. Block has conducted extensive research on the sulfur compounds of garlic
at the State University of New York at Albany. In 25 years of studying sulfur-containing
compounds, he has authored more than l20 scientific articles. He received
his Ph.D. from Harvard University with Nobel Laureate E. J. Corey.
Passwater: We have known of garlic's health benefits for thousands of years,
but recently I've noticed an increased interest in garlic research. Now
that you and other scientists have elucidated the key aspects of the chemistry
of garlic that help explain how garlic actually brings about these benefits,
garlic is beginning to receive wider attention from nutritionists. Besides
"folklore," what suggestions or evidence have we had that garlic
has major health benefits?
Block: Epidemiological and medical studies suggest that individuals regularly
consuming garlic show a lower incidence of stomach cancer, have longer blood
clotting times and show lower blood lipid levels (which indirectly translates
into reduced risk of stroke and cardiovascular disease).
Passwater: Do these people generally eat raw or cooked garlic, or both?
Block: Garlic is generally processed in some way, such as by cooking, or
is cut and mixed with salad oil. Some people do eat garlic raw although
this is not recommended.
Passwater: You don't recommend eating raw garlic?
Block: Not by itself. Raw garlic can be very irritating and could injure
the digestive tract.
Passwater: Sulfur compounds tend to be very fragile and volatile. Do many
of the beneficial garlic sulfur compounds survive cooking?
Block: Some do and some don't. In point of fact, cooking can convert the
more fragile sulfur compounds into other sulfur compounds which are also
beneficial and at the same time are a bit more robust.
Passwater: Okay, let's talk about the sulfur compounds present in garlic
and what happens to them.
Block: Sulfur compounds from fresh garlic can be divided into five categories:
l. The stable, odorless derivatives of the natural, sulfur-rich amino acid
known as cysteine, found in unbroken garlic cloves and bulbs. Alliin (pronounced
al-lean) is an example of this type of compound.
2. Compounds with a very brief existence called intermediates (the chemical
equivalents of shooting stars), formed when we cut, crush, or chop garlic
cloves thereby freeing an enzyme (allinase is the name of the garlic enzyme),
which acts on the cysteine compounds such as alliin. We know little about
the intermediates for they disappear in a fraction of a second after being
formed and can never be stored even at low temperatures.
3. The isolable but none-the-less unstable and reactive compounds having
a typical fresh garlic aroma and taste, formed by very rapid joining together
of intermediates and found both in garlic juice as well as in the air above
chopped garlic. Allicin, (pronounced "alice-in") is a well known
example of compounds of this type. Actually our recent research has shown
that as many as nine "chemical cousins" of allicin are also formed
when garlic is cut. These other compounds also have a typical garlic aroma
and taste. While allicin and its "cousins" can be prepared in
pure form and studied in the research laboratory, they are termed "unstable
compounds" meaning that at room temperature they have a very limited
shelf life (a few hours) and cannot be stored without using special low
temperature refrigerators.
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Richard A. Passwater, Ph.D. has been a research biochemist since 1959. His first areas of research was in the development of pharmaceuticals and analytical chemistry. His laboratory research led to his discovery of 
