Garlic (Allium sativum)

Latin name: Allium sativum L. [Liliaceae]
Plant part: Bulb

Garlic has been used as a medicine for more time and by more cultures
than perhaps any other plant. Garlic is unique in its high sulfur
content, which is four times greater than that of the other high sulfurcontaining
vegetables and fruits, such as onion, broccoli, cauliflower,
or apricots. The most abundant sulfur compound in garlic is alliin,
which is typically present at 10 mg per gram fresh weight. When garlic
cloves are cut, crushed, or chewed there is a conversion, within
seconds, of alliin to allicin by the enzyme allinase. Allicin is thought
to be important to the beneficial effects of garlic and is also responsible
for its characteristic odor. Therapeutic effects are also attributed
to other sulfur compounds (Lawson, 1996).

Garlic powder is the product most similar to fresh cloves in chemical
composition, as it is dehydrated at a low oven temperature and
then pulverized. When carefully prepared, the allinase activity is
preserved. A very important aspect of the effective quality of garlic
powder products is that allicin can be formed after consumption.
Therefore, many garlic supplements are standardized to their “allicin potential.”
Because the enzyme allinase, necessary to produce allicin, is
destroyed by the acidic pH of the stomach, many garlic preparations
are enteric coated. This coating delays dissolution of the capsule or
tablet until it reaches the intestine (Lawson, 1996).

Allium sativum

Aged garlic extract (AGE) is prepared by storing sliced garlic in 15
to 20 percent aqueous ethanol for 18 to 20 months. After this time, the
liquid is filtered and concentrated. Most of the sulfur compounds responsible
for the characteristic garlic odor are removed during processing.
There are few allicin or alliin-derived compounds. The sulfur
compound measured for quality purposes is S-allylcysteine. Aged
garlic extract is available in both liquid and dry forms. The liquid
form contains 10 percent ethanol (Lawson, 1996). Kyolic® Aged
Garlic Extract™ is provided byWakunaga of America Co., Ltd. The
trials reviewed used both dry and liquid forms; however, the doses
used in the trials were much higher than those suggested in the available
product literature.

Garlic contains only a very small amount of oil-soluble compounds.
Commercial garlic oil is produced by steam distillation of
chopped garlic, a process that converts allicin and other thiosulfinates
to oil-soluble allyl sulfides. Garlic oils are also prepared by maceration
with organic solvents or common plant oils such as soybean oil.
Garlic oils contain mostly alliin-derived compounds. In addition,
vinyldithiins and ajoene are present. Garlic oils are not usually characterized
by their sulfide content, but tend rather to be promoted as
containing a specific amount of “pure garlic oil” (Lawson, 1996).

Clinical trials using garlic preparations have mostly focused on the
possible reduction in risk for atherosclerotic heart disease. Elevated
plasma (blood) lipids (cholesterol and triglycerides) are considered
risk factors for heart disease, and much of preventative treatment has
focused on lowering these levels to within parameters considered
normal.
Sources for cholesterol are dietary intake of animal fats and production
by the liver. Cholesterol is transported in the blood by lipoproteins,
and the major categories of lipoproteins are very low-density lipoproteins
(VLDL), low-density lipoproteins (LDL), and high-density
lipoproteins (HDL). VLDL and LDL transport fats, primarily triglycerides
(TG) and cholesterol, from the liver to cells throughout the
body. Elevations of either VLDL or LDL are associated with an increase
in risk for developing atherosclerosis, a primary cause of heart
attack and stroke. The role of HDL is to return fats to the liver. Hence
the ratios of total cholesterol (TC) to HDL cholesterol and LDL to
HDL indicate whether cholesterol is being deposited into tissues or
broken down and excreted. It is recommended that total serum cholesterol
be less than 200 mg/dl, LDL be less than 130 mg/dl, HDL
cholesterol be greater than 35 mg/dl, and triglyceride levels be less
than 150 mg/dl (Pizzorno and Murray, 1999).