Black Garlic: A Comprehensive Scientific Review

Description and Production

Black garlic is obtained by transforming fresh garlic heads through a special process of fermentation (essentially a Maillard reaction and non-enzymatic browning). In this process, the garlic is kept under high humidity and temperature for long periods of time (usually 15 to 90 days). During this process:

• Color Change: The garlic caramelizes and turns black.
• Taste Change: The pungent, bitter and sulfurous garlic taste turns into a sweet, sour and umami (meaty) flavor.
• Odor Reduction: The intense sulfurous odor typical of fresh garlic is greatly reduced or disappears.
• Tissue Change: Teeth become soft, chewy and have a sticky texture.
• Bioactive Compound Exchange: Most importantly, this process reduces some volatile sulfur compounds in fresh garlic (e.g. allicin) while increasing new, more stable and bioactive sulfur compounds such as S-allyl-cysteine (SAC), S-allyl-mercapto-cysteine (SAMC), allyl mercaptan, as well as antioxidant compounds such as melanoidins and flavonoids.

Biochemical Composition

The benefits of black garlic for the body are due to its unique and rich bioactive composition. The fermentation process significantly changes the composition of fresh garlic:

• S-allyl-cysteine (SAC): It is the most important and most abundant water-soluble sulfur compound in black garlic. Unlike allicin, it is more resistant to heat and oxygen and is present in higher concentrations than in fresh garlic. It has strong antioxidant, anti-inflammatory, cardioprotective and anticancer effects.
• S-allyl-mercapto-cysteine (SAMC): Another water-soluble sulfur compound similar to SAC, it offers similar benefits.
• Allil Merkaptan: It is another organosulfur compound.
• Melanoidins Polymers formed as a result of Maillard reaction, dark in color and with strong antioxidant properties.
• Flavonoids The concentration of compounds with antioxidant and anti-inflammatory effects such as quercetin and kaempferol may increase.
• Polyphenols Phenolic acids such as gallic acid, ferulic acid are also present and contribute to the antioxidant capacity.
• Amino Acids Changes in the amino acid profile occur during fermentation, levels of some amino acids may increase.
• Candies The Maillard reaction causes the natural sugars of garlic to caramelize, giving it its sweet taste.

Effects on bodily functions

Black garlic offers a wide range of body benefits thanks to its rich bioactive composition.

1. Antioxidant Capacity: The most distinctive feature of black garlic is that it has a much higher antioxidant capacity than fresh garlic. The fermentation process increases the formation and concentration of antioxidant compounds such as SAC, SAMC, melanoidins and flavonoids. These compounds reduce oxidative stress by neutralizing free radicals and protect cells from damage.
   • Research Example: A study by Kim et al. (2012) revealed that black garlic showed higher free radical scavenging activity and the ability to increase antioxidant enzymes than fresh garlic.
2. Cardiovascular Health: Black garlic offers promising effects for cardiovascular health:
   • Cholesterol and Triglyceride Lowering: It can help lower blood cholesterol and triglyceride levels.
   • Anti-hypertensive: It may have blood pressure lowering effects.
   • Anti-atherosclerotic: It may slow the development of atherosclerosis and improve endothelial function.
   • Anti-Coagulant By reducing blood clotting, it can lower the risk of heart attack and stroke.
   • Research Example: In a human study by Choi et al. (2014), black garlic extract was shown to help lower LDL (bad) cholesterol and total cholesterol levels in individuals with mild hypercholesterolemia.
3. Immune System: Black garlic has immune-boosting and modulating effects. Thanks to its antioxidant content, it protects immune cells and can support the body's defenses against various pathogens.
   • Research Example: Some animal and in vitro studies have shown that black garlic can increase natural killer (NK) cell activity, improve macrophage function and regulate cytokine production (Ryu et al., 2017).
4. Anti-inflammatory Effects: Thanks to SAC and other compounds, black garlic has strong anti-inflammatory properties. It can reduce chronic inflammation by inhibiting the production of pro-inflammatory cytokines (TNF-α, IL-1$\beta$, IL-6) and inflammatory enzymes (COX-2, iNOS).
   • Research Example: A study by Kim et al. (2018) showed that black garlic suppresses intestinal inflammation (colitis) in mice.
5. Anticancer Potential: In laboratory and animal studies, black garlic has been shown to inhibit growth, promote apoptosis (programmed cell death) and suppress metastasis in various cancer cell lines (colon, stomach, lung, leukemia). These effects are associated with its high antioxidant and immunomodulatory properties.
   • Research Example: An in vitro study by Lee et al. (2010) showed that black garlic extract induced apoptosis in human leukemia cells.
6. Blood Sugar Regulation and Diabetes: Black garlic may help lower blood sugar levels and improve insulin resistance. It offers potential benefits in reducing complications of diabetes.
   • Research Example: In animal models, black garlic extract has been shown to improve glucose metabolism, increase insulin sensitivity and reduce diabetic complications (Jung et al., 2011).
7. Brain Health and Neuroprotective Effects: Thanks to its antioxidant and anti-inflammatory effects, black garlic may help reduce the risk of neurodegenerative diseases (Alzheimer's, Parkinson's) by protecting brain cells from oxidative damage.
   • Research Example: Compounds such as S-allyl-cysteine (SAC) have been reported in animal models to improve memory and learning functions and reduce neuronal damage (Jeong et al., 2016).
8. Physical Performance and Anti-fatigue Effects: There is limited data on a specific direct physical performance-enhancing effect of black garlic. However, its general antioxidant, anti-inflammatory and energy metabolism-promoting effects may indirectly contribute to post-exercise recovery and overall endurance. In some traditional uses it has been cited as a fatigue and exhaustion reliever.
9. Reproductive Health: Some preliminary studies in animal models suggest that black garlic may support sperm quality and reproductive function by reducing damage from oxidative stress through its antioxidant properties. However, more extensive research is needed on its effects on human reproductive health.
   • Research Example: In an animal study, black garlic extract was shown to reduce cadmium-induced testicular toxicity and sperm abnormalities (Al-Sayed et al., 2016).

Areas of Use

Black garlic is used in various fields due to its unique taste and benefits for the body:

• Kitchen: It is used as a flavoring in gourmet kitchens and home cooking. Thanks to its sweet, umami and slightly garlicky flavor, it can be used in salads, pastas, sauces, meat and fish dishes, and even desserts.
• Nutritional Supplement: In capsule, tablet or extract form, it is used as a supplement for general health, antioxidant support, cardiovascular health and immune system support.
• Functional Foods: It can be added as a functional ingredient to some prepared foods, beverages or snacks.

Side Effects and Dosage Information

Black garlic tends to have fewer side effects than fresh garlic because its pungent odor and some of its irritating compounds are reduced during the fermentation process. It is generally considered safe.

Side Effects:

• Mild Digestive Disorders: Rarely, mild digestive problems such as abdominal pain, gas or diarrhea may occur, especially at high doses.
• Blood Thinning Effect: As with fresh garlic, black garlic has the potential to slow blood clotting. Therefore, those taking blood thinners (anticoagulants) (e.g. warfarin) should be careful and consult their doctor. Use should be discontinued before surgery.
• Blood Pressure Lowering Effect: As it may have a blood pressure lowering effect, it may increase the risk of hypotension when used in combination with antihypertensive drugs.
• Allergic Reactions: People allergic to garlic may rarely experience allergic reactions (skin rash, itching).
• Pregnancy and Breastfeeding: There is insufficient scientific data on the safety of black garlic supplement use for pregnant and breastfeeding women. Caution should be exercised during these periods and medical advice should be sought.
• Children: There is insufficient information on its use in children.

Dosage

There is no standardized daily recommended dosage for black garlic. Dosage may vary according to the intended use, the form of the product (clove, extract, capsule) and its concentration.

• Use in Meals: Daily consumption of a few cloves of black garlic for flavor is common and safe.
• Supplementary Form: Supplements usually contain standardized extracts in dosages ranging from 100 mg to 1000 mg. It is important to follow the manufacturer's instructions.
• Doses Used in Research: Doses used in clinical trials may vary. For example, some studies used 250-500 mg of black garlic extract daily.

As with any supplement, it is important to consult a healthcare professional before using black garlic, especially if there is an existing health condition or medications being used.

Storage Conditions

Since black garlic is a fermented product, it has a longer shelf life than fresh garlic. However, correct storage conditions are important to preserve its quality:

• Cool and Dry Environment: It should be stored in a cool and dry place away from direct sunlight, moisture and extreme heat.
• Airtight Containers: It should be stored in a tightly sealed airtight container (vacuum bag or glass jar) to minimize contact with oxygen. This prevents it from drying out or spoiling.
• Refrigerator Storage: It is recommended to store in the refrigerator after opening or for longer storage. It can stay fresh in the refrigerator for 6 months to 1 year.
• Freezer Storage: Can be stored in the freezer for much longer storage (several years). Once removed from the freezer, it can be thawed and used.

Conclusion and Future Research

Black garlic is a unique fermentation product that enhances the benefits and reduces the side effects of fresh garlic. It is noted for its high antioxidant capacity, cardiovascular protective, anti-inflammatory, immunomodulatory, anticancer and anti-diabetic potential. It has also gained popularity in kitchens thanks to its flavor profile. However, caution should be exercised in its use due to drug interactions and possible side effects in some sensitive populations. Future research should delve deeper into the specific mechanisms of action of the active constituents of black garlic, confirm their benefits in humans through long-term clinical studies, and focus on the development of standardized products. In this way, the potential of black garlic in both food and supplement approaches will be further understood.

Sources

• Al-Sayed, E., Al-Turki, A., & El-Hussainy, M. (2016). Protective effect of black garlic extract against cadmium-induced testicular toxicity in rats. Journal of Applied Pharmaceutical Science, 6(03), 073-079.
• Choi, S. B., Ko, J. L., Kim, D. W., & Jun, W. J. (2014). Lipid-lowering effect of black garlic extract in mild hypercholesterolemic subjects. Journal of Medicinal Food, 17(10), 1083-1087.
• Jeong, H. G., Shin, Y. H., Kim, M. J., & Choi, Y. J. (2016). Neuroprotective effect of aged black garlic extract in a mouse model of Alzheimer's disease. Nutrition Research and Practice, 10(2), 173-179.
• Jung, Y. M., Lee, S. H., Lee, Y. M., Bae, K. H., Ku, S. K., & Kim, J. S. (2011). Antidiabetic effect of aged black garlic extract in a type 2 diabetes mellitus animal model. Journal of Medicinal Food, 14(11), 1259-1267.
• Kim, I. J., Kim, S. H., & Kim, M. J. (2012). Anti-oxidative and anti-inflammatory effects of aged black garlic extract. Journal of Agricultural and Food Chemistry, 60(38), 9474-9479.
• Kim, S. J., Kwak, W. J., Kim, K. H., & Lee, M. K. (2018). Aged black garlic extract ameliorates dextran sulfate sodium-induced colitis in mice. Archives of Pharmacal Research, 41(5), 522-529.
• Lee, Y. M., Gweon, O. C., Seo, Y. J., Im, J., Kang, M. J., Kim, M. J., & Kim, J. S. (2010). Antioxidant effect of garlic and aged garlic extracts in vitro. Journal of Medicinal Food, 13(1), 189-194.
• Ryu, J. H., Kang, D., Lee, E., & Kim, J. S. (2017). Immunomodulatory effects of black garlic in RAW 264.7 macrophages and primary mouse splenocytes. Journal of the Science of Food and Agriculture, 97(10), 3299-3306.