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Supplement: Recent Advances on the Nutritional Effects Associated with the Use of Garlic as a Supplement

A Commentary on the Effects of Garlic Extraction and Formulation on Product Composition¹

Plants Personified, Incorporated, Minneapolis, MN 55418 and ^* College of Pharmacy, University of Minnesota, Minneapolis, MN 55455

²To whom correspondence should be addressed. E-mail: staba001{at}tc.umn.edu.

ABSTRACT

The garlic (Allium sativa L.) bulb has been used as a food and condiment for centuries throughout the entire world and in Egypt for perhaps 5000 years. Since the passage of the Dietary Supplement Health and Education Act (DSHEA) of 1994 by the U.S. Congress, it has been claimed that garlic dietary supplements possess health benefits. Support for this claim is not the primary objective of this publication. The primary objective of this article is to demonstrate that the prediction of a potential health benefit(s) from garlic is largely dependent on the process used to produce a product.

KEY WORDS: • garlic • formulation • chemistry • standardization

Hundreds of chemical substances are present in fresh, dried garlic or extracts. Significant synergy or antagonism of the garlic substances, or their artifacts, on human physiology may exist and vary with an individual’s age, pathology, dosage regimen and possible drug, food or metabolite interactions. Our long historical experience of garlic consumption has satisfied many individuals and entities that the human risk-to-benefit ratio is beneficial, although human allergic reactions, gastric distress, topical sensitivities and increased blood coagulation times are not uncommon.

Garlic product processes.

The chemicals present in a garlic product are largely dependent on the following: the potential substrate activity of the enzyme allicinase, which is sequestered within garlic cell vacuoles; the temperature and duration of drying; the use of polar and/or nonpolar extraction solvents; and the conditions and period of maceration before final extraction. A very significant reaction occurs when garlic cells are crushed, allowing alliinase to interact with alliin to form allicin. Alliinase is denatured by heat, at a pH of < 3.5, such as that in the stomach, and by many nonpolar solvents (Koch and Lawson 1996 ).

The major processes used are the following:

1. Freeze-drying. The freeze-drying of fresh garlic cloves is a method of flash evaporation at low temperature in a partial vacuum. This method results in virtually no changes in chemical composition, and the resulting product is often used for culinary purposes.

2. Low Temperature Drying. This process involves drying sliced fresh cloves at temperatures <50°C for 3–4 d. Some allicin is formed due to the slicing process. Allicin is converted to allyl sulfides, which are largely responsible for the typical garlic odor. The final product has many of the attributes of the fresh garlic clove, which include -glutamyl cysteine, the precursor to allin and S-allylcysteine.

3. Distillation. Steam-distilled garlic contains principally allyl sulfides. Allicin is volatile and may be lost or converted to the allyl sulfide degradation compounds. The oil generated may be dissolved in soybean oil or other vegetable oils to form a product.

4. Maceration in Oil. Chopped garlic is homogenized and slowly extracted (maceration) in soybean or another vegetable oil. Such products contain vinyldithins, allyl sulfides and ajoene.

5. Hydroalcoholic Short Extraction. The stability of the constituents of fresh or dried garlic extracted with a hydroethanolic solution for a short maceration time is questionable. The resulting product is often referred to as a Tincture, and may be made in 10, 20 or 30% wt/v concentrations in 70% ethanol. It is also possible to manufacture fluid extracts or dry extracts that would be expressed as the ratio of the garlic material used to the volume or weight of the final product. For example, a 1:1 fluid extract would contain the constituents of 1 g garlic:1 mL of finished product. The stability of the constituents in fluid extracts and dry extracts and their final chemical content could be variable.

6. Hydroalchoholic Long Maceration. Sliced garlic is placed in 20% ethanol and macerated for a long period of time (6–20 mo), filtered and concentrated. Allicin is completely converted to allyl sulfides, including diallyl disulfides, diallyl trisulfide and allyl methyl trisulfide, which are largely all volatilized or converted to other compounds. A major ingredient of this process is S-allylcysteine (Lachance 1997 ).

Dosage forms and potential therapeutic effect(s)

If a whole garlic clove is crushed and then ingested, the individual will receive the following: quantities of alliinase and its primary substrate alliin; allicin and its allyl sulfide volatile conversion products; some -glutamyl cysteine and S-allylcysteine; and the largely nonpolar compounds, vinyldithiins and ajoene. An adult dose of garlic often suggested is one fresh clove weighing 4000 mg (Blumenthal et al. 1998 ).

The consequences of garlic clove consumption may be gastrointestinal discomfort and the formation of a generally undesirable odor in the breath and skin perspiration. Compounds such as allicin, allyl sulfides, allyl mercaptans and terpenes are most responsible and will vary in their concentration in the undesirable odor over time.

Products that have been properly enteric-coated to resist the stomach acids may form allicin in the small intestine if active alliinase is present, and possibly protect ajoenes and the vinyldithiins. The presence of undesirable odors may be delayed or altered in quality.

The effects of various sulfur-containing compounds from garlic as human antilipolytics, anticancer and antimicrobial preventatives or drugs continues to be examined. The pharmacokinetic significance of alliinase and its derivatives is largely unknown. Although it is possible that excess intake of garlic products may promote orthostatic hypotension in individuals consuming antihypertensive agents, or may promote hypoglycemia in those receiving insulin or oral hypoglycemic medications, the vast majority of individuals will likely not experience these difficulties. Similarly, the mechanism of action of organosulfur component may involve several enzymes; thus, there is a possibility of cumulative interactions.

Standardization, fingerprinting, and product comparisons

Products must be standardized. The presence of a variety of products with seemly different intended purposes may make it difficult to establish only one component for standardization. It appears that the major use of standardizing a product is to ensure lot-to-lot product uniformity and not necessarily beneficial health outcomes. The manufacturer’s assurance of an identical or similar end point of a commercial process should involve fingerprinting by establishing a chemical and/or biological profile of the garlic raw material and its final product(s) (Lash and Staba 1999 ).

Before a product is used for a beneficial health effect, it would be desirable to know the starting garlic material, its content of key sulfur constituents both polar and nonpolar, and total quantity of sulfur-containing compounds per dosage unit. Much of the variability in the literature may revolve around uncertainties in amounts of polar and nonpolar constituents in the product provided. Clearly, greater attention must be given to clarifying the types and amounts of active compounds in the various products that are commercially available.

FOOTNOTES

¹ Presented at the conference "Recent Advances on the Nutritional Benefits Accompanying the Use of Garlic as a Supplement" held November 15–17, 1998 in Newport Beach, CA. The conference was supported by educational grants from Pennsylvania State University, Wakunaga of America, Ltd. and the National Cancer Institute. The proceedings of this conference are published as a supplement to The Journal of Nutrition. Guest editors: John Milner, The Pennsylvania State University, University Park, PA and Richard Rivlin, Weill Medical College of Cornell University and Memorial Sloan-Kettering Cancer Center, New York, NY.

REFERENCES

1. Blumenthal M., Busse W. R., Gruenwald J., Hall T., Riggins C. W., Rister R. S. The Complete German Commission E 1998 Monographs p. 685. Integrated Medicine Communications, Boston, MA.

2. Koch H. P., Lawson L. D. Garlic: The Science and Therapeutic Application of Allium sativum L. and Related Species 2nd ed. 1996:329 William and Wilkins Baltimore, MD.

3. Lachance P. A. Designer Foods III: Garlic, Soy, and Licorice 1997 Nutrition Press Trumbull, CT.

4. Lash, L. J. & Staba, E. J. (1999) Garlic Dietary Supplements: An Assessment of Product Information Provided by Garlic Manufacturers. J. Minn. Pharm. Assoc. (in press).

5. Staba E. J., Staba J. E. Commentary: a personal overview of herbal medicine practice in the U.S.A. J. Minn. Pharm. Assoc. 1998;52:9, 12, 22–24

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