The Medicinal Values of Garlic - from Clove to Circulation

 Title: The Biochemistry and Pharmacology of Garlic: From Clove to Circulation

by: Lin Ru Wu alias Lim Ju Boo

 

In the mid 1960's I was doing my postgraduate in Nutrition at the University of London when one of my professors mentioned about the medicinal values of garlic. Today, I like to share further knowledge I gained  there about this valuable medicinal  clove 

Abstract:

Garlic (Allium sativum) has been revered since antiquity for its culinary and medicinal properties. This paper explores the biochemical transformation of garlic's sulfur compounds, particularly allicin and ajoene, through mechanical processing, digestion, and hepatic metabolism. It discusses the pharmacologically active derivatives of garlic, their bioavailability, and the evidence-based therapeutic doses. By synthesizing findings across food chemistry, enzymology, and clinical pharmacology, this work aims to serve as a concise but comprehensive resource for doctors, nutritionists,  healthcare enthusiasts and scholars

1. Introduction:

Garlic is widely recognized for its diverse medicinal applications, including antimicrobial, cardiovascular, and anticancer effects. These properties are attributed to sulfur-containing compounds formed upon cellular disruption of garlic tissues. While traditional knowledge praises garlic's benefits, understanding the journey of its bio-actives from raw clove to systemic circulation requires a multidisciplinary approach.

2. Allicin Formation: The Moment of Activation

Allicin is not present in intact garlic cloves. Upon mincing or crushing, the enzyme alliinase converts the stable compound alliin into allicin within 5 to 10 minutes. This enzymatic reaction is highly sensitive to:

• Heat (>60°C), which denatures alliinase

• Acidity, which can reduce enzyme efficiency

Reaction Pathway: Alliin (S-allyl-L-cysteine sulfoxide) + Alliinase → Allicin (diallyl thiosulfinate)

Waiting 10 minutes after crushing allows maximal allicin formation before further cooking or ingestion.

3. Stability and Degradation of Allicin

Allicin is unstable, reactive, and decomposes quickly into secondary sulphur compounds, including:

• Ajoene (anti-platelet, antifungal)

• Diallyl disulfide (DADS)

• Diallyl trisulfide (DATS)

• S-allyl cysteine (SAC) (stable, bioavailable in aged garlic)

Heat, time, and pH conditions all influence the breakdown pathway.

4. Oral Processing vs Mechanical Mincing

Chewing garlic activates alliinase, but swallowing too quickly reduces time for full allicin conversion. Saliva does not appear to inactivate alliinase significantly, but the enzymatic activity is more reliable in a controlled setting (e.g., mincing and waiting 10 minutes).

5. Gastrointestinal and Hepatic Fate

In the digestive tract:

• Allicin is mostly degraded in the stomach
• Derivatives like DADS, DATS, ajoene, and SAC survive and are absorbed

In the liver:

• Some compounds are metabolized but retain activity

• SAC is especially bioavailable and used in standardized supplements

6. Pharmacological Activity and Effective Doses

Compound	Effective Dose	Activity
Allicin	20–50        mg/day	Antimicrobial,                       antihypertensive
Ajoene	~10–25         mg/day	Antithrombotic,                   antifungal
SAC	Varies	Antioxidant, anti-                 inflammatory

Garlic supplements are typically standardized to 1.3% allicin content or 3.6 mg per 600 mg tablet. But this value may not be stable on storage as for garlic pills. I shall talk on this later.  

7. Preparation Guidelines for Maximum Medicinal Value

Method	Allicin Yield	Notes
Mince + wait 10 min + consume raw	Maximum	Best for medicinal use
Chewing raw garlic	Moderate	Faster ingestion limits yield
Cooking after 10 min rest	Mild	Low heat preserves some value
Aged garlic extract	High (SAC)	Ideal for long-term supplementation

8. Conclusion

While allicin itself is ephemeral, its derivatives may or may not persist and contribute meaningfully to garlic's therapeutic potential. For instance, from the very beginning I mentioned that in the mid 1960's when I was doing my postgraduate in Nutrition at the University of London when one of my professors mentioned about the medicinal values of garlic. But he also told us that they took over two dozens different types of garlic pills manufactured by various companies from various parts of the world and analyzed them for the presence of ajoene, the derivative of allicin since allicin is not stable. What the researchers at London University found was, even ajoene which was supposed to be more stable was not present in any of those hundreds of garlic pills. This implied that even the derivatives of allicin - ajoene is not stable when the garlic was processed into pill form or when stored in a bottle for sales. Probably garlic pills were  just oils - like any vegetable oil with no medicinal values in them?  

My strong advised is, when raw garlic has been minced or crushed, wait for at least 10 minutes for the enzyme alliinase to release the allicin and consume immediately - not longer than a few hours later. We are unsure if storing the minced raw garlic in a refrigerator will retain its medicinal values - allicin and its derivatives - DADS, DATS, ajoene, and SAC, since as far as I know, no study has been done on this. 

Understanding garlic as a sequence of biochemical transformations, from mechanical activation to hepatic metabolism, enables more effective use of this ancient botanical medicine.

References

1. Amagase H, Petesch BL, Matsuura H, Kasuga S, Itakura Y. Intake of garlic and its bioactive components. J Nutr. 2001 Mar;131(3s):955S-962S.

2. Lawson LD, Wang ZJ. Allicin and allicin-derived garlic compounds increase breath acetone through allyl methyl sulfide: Use in measuring functional allicin in garlic. J Agric Food Chem. 2005;53(6):1974-1983.

3. Dirsch VM, Kiemer AK, Wagner H, Vollmar AM. Effect of allicin and ajoene, two compounds of garlic, on inducible nitric oxide synthase. Atherosclerosis. 1998;139(2):333-339.

4. Rahman K. Effects of garlic on platelet biochemistry and physiology. Mol Nutr Food Res. 2007;51(11):1335-1344.

5. Iciek M, Kwiecien I, Wlodek L. Biological properties of garlic and garlic-derived organosulfur compounds. Environ Mol Mutagen. 2009;50(3):247-265.

Acknowledgments:

 Special gratitude to my friend and colleague, Professor Sage for his additional inputs that has inspired me to write this paper