Author: AlivitPharm
A Small Clove, a Wealth of Bioactive Compounds
Garlic is a staple of everyday cooking, valued for its distinctive aroma and flavour, but it is much more than a seasoning. For thousands of years, it has also been part of traditional approaches to health, long before modern science was able to explain its composition or how individual compounds may act. It has been used across different cultures, with knowledge and experience of its use passed down from generation to generation.
Today, we have a much broader understanding of garlic’s composition and the processes that take place within it. This allows us to better understand why this familiar food has attracted scientific interest for decades. Garlic contains a wide range of bioactive compounds, some of which are the subject of intensive research.
A Closer Look at Garlic
Behind its familiar flavour and aroma lies a plant that is far more complex than it may initially appear.
Garlic (Allium sativum) is a perennial herbaceous plant belonging to the family Amaryllidaceae and the genus Allium, which also includes onions, leeks and chives. Its best-known part is the underground bulb. The bulb consists of multiple cloves packed closely together and enclosed by dry protective outer layers. These may be white, greyish or purple, depending on the variety. Each clove is itself covered by a thin protective skin.
Long, narrow and flattened green leaves emerge from the bulb. In certain varieties, a flowering stalk develops, bearing an inflorescence with small flowers. In some types of garlic, small aerial bulbs, or bulbils, may also develop on the stalk and can be used for propagation.
- The cloves are the part most commonly consumed. Their composition is not always the same. It can be influenced by the variety, growing conditions, maturity, storage, and also by how the clove is handled after harvest.
A large number of bioactive compounds have been identified in garlic. These include alliin, allicin, ajoenes, vinyldithiins, diallyl disulfide, diallyl trisulfide and S-allyl cysteine. Some of these compounds are formed or undergo changes only after processing, which means that the chemical composition of a fresh clove differs from that of, for example, a garlic extract.
These compounds are not merely chemical names. They contribute to garlic’s characteristic aroma and flavour and are also part of the reason why its properties and potential effects on health have attracted so much scientific interest.
The composition of garlic is not the same under all conditions. Its characteristics can be influenced by variety, soil, climate, cultivation practices and storage. An interesting example is the garlic grown in Ljubinje, in Herzegovina. The local population of spring garlic, known as Saransak, is characterised by distinctive morphological traits and good adaptation to local agroecological conditions. Research has demonstrated favourable agronomic characteristics of this population, making Saransak a valuable genetic resource with potential for further cultivation and breeding programmes (Todorović et al., 2025).
Saransak garlic from Ljubinje also has a wider reputation: in 2018, Radio Television of Serbia (RTS) reported that “Saransak from Ljubinje in Herzegovina is among the five best in the world,” citing a statement by a technologist at a garlic-processing plant. The same source also reported claims about its nutritional value in comparison with the more expensive French garlic (👉 RTS – Herzegovinian Garlic Prepares for a Passport to Europe).
Black Garlic is produced through a controlled fermentation process that changes its composition, flavor, aroma, and texture. Fermentation may enhance the availability of certain bioactive compounds while contributing to garlic’s distinctive sensory profile. Research also indicates notable antioxidant activity in fermented black garlic.
From Traditional Use to Modern Research
Garlic has a long history of traditional use. The European Medicines Agency (EMA), in its monograph on Allium sativum L., bulbus, lists the traditional use of certain garlic preparations for the relief of symptoms of the common cold.
- It is important, however, to understand what “traditional use” means. It does not mean that a particular effect has been demonstrated in the same way as the efficacy of a medicine established through clinical trials. Rather, it refers to use based on longstanding experience, together with regulatory recognition of traditional use on the basis of available evidence.
Extra caution is warranted when using concentrated garlic preparations. Garlic supplements may increase the risk of bleeding, particularly in people taking medicines that affect blood clotting, such as anticoagulants and aspirin. It is therefore important to inform a physician or other healthcare professional about their use, especially before undergoing surgery.
One of the most interesting moments in the story of garlic occurs when the clove is damaged. In an intact clove, alliin and the enzyme alliinase are physically separated.
When a clove is cut or crushed, alliin and alliinase come into contact and a reaction begins in which allicin is formed. This reaction leads to the formation of compounds characteristic of garlic’s aroma and flavour. Allicin is one of the best-known sulphur compounds formed in this process. However, it is not stable. Once formed, it changes relatively quickly and is converted into other sulphur compounds, including diallyl disulfide, diallyl trisulfide, ajoenes and vinyldithiins.
- For this reason, garlic is chemically different before and after processing. Cutting, crushing, cooking, drying and other forms of processing can alter the composition and quantity of its bioactive compounds. The final composition is also influenced by variety, growing conditions and storage.
This is important when interpreting research findings as well. A result obtained using freshly crushed garlic cannot automatically be applied to garlic powder, garlic oil, aged garlic extract or another preparation. Different products may contain different sulphur compounds and different amounts of those compounds. Studies of commercial garlic preparations have demonstrated substantial differences in their chemical composition.
Laboratory studies have shown that certain sulphur compounds in garlic possess various biological properties, including antimicrobial and antioxidant activity. However, what is observed in the laboratory does not automatically translate into the same effect in the human body. Between a laboratory finding and an effect in the human body, factors such as dose, compound stability, absorption and metabolism, as well as the form of the preparation itself, can all influence the outcome.
This is why the story of allicin is not simply the story of a single compound. It illustrates how the way garlic is cut, crushed, heated or otherwise processed can alter what it contains and, consequently, what is being studied when researchers investigate its potential health effects.
Immunity and the Common Cold
As noted above, the European Medicines Agency lists the relief of common cold symptoms among the traditional uses of certain garlic preparations. However, once we move from traditional use to clinical research, the picture becomes more complex. Garlic is often said to “boost the immune system”, but such a claim is not easy to substantiate. The immune system is not something that can simply be “boosted”; rather, it is a complex system involving numerous interconnected processes.
Laboratory studies suggest that certain garlic compounds may affect different microorganisms and immune processes. However, an effect observed in the laboratory does not automatically mean that the same effect will occur in the human body.
When it comes to the common cold, there have also been several clinical studies, but the evidence remains limited. It is therefore not justified to claim that garlic reliably prevents or treats the common cold, or that it simply “boosts immunity”. More precisely, there are interesting laboratory findings and some clinical evidence, but there is still insufficient high-quality research to draw a firm conclusion.
Between Experience and Scientific Evidence
Garlic is safe for most people when consumed as part of a normal diet. Larger amounts, particularly of raw garlic, may cause heartburn, abdominal discomfort, bloating or nausea in some people.
It is also important to recognise that experience with one garlic preparation cannot automatically be applied to another. Fresh garlic, garlic powder, garlic oil, aged garlic extract and standardised preparations have different compositions and different concentrations of individual compounds. Natural origin alone does not guarantee that something is safe for everyone. As with other preparations, the amount used, method of administration, composition and health status of the individual all matter.
Garlic is one of those foods we have known for almost all our lives, yet there is still much about it that we are only beginning to understand. Its characteristic aroma is not simply a matter of taste—it is the result of a series of chemical reactions that begin when the clove is damaged. Alliin, alliinase, allicin and other sulphur compounds are all part of this story.
When discussing the health properties of garlic, it is important to distinguish between findings from laboratory research, results from studies in humans and traditional use. Modern research seeks to determine which of the effects traditionally attributed to garlic are supported by experimental and clinical evidence.
Behind all of this lies a seemingly ordinary clove of garlic…
Literature
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Disclaimer: This article is intended for informational and educational purposes only and does not constitute medical advice or a substitute for professional medical consultation.
The visual material accompanying this article was generated using artificial intelligence and serves an illustrative rather than documentary purpose.
