The antioxidant activities of natural products have been widely evaluated, such as fruits, vegetables, mushrooms, cereal, flowers, and wild fruits. Accumulating studies have found that garlic has strong antioxidant properties. A study evaluated the antioxidant capacities of both raw and cooked garlic, and found that the raw garlic exhibited stronger antioxidant activity. Stir-fried garlic was also shown to have stronger antioxidant capacities, indicating that the processing could affect the antioxidant property of garlic. In another study, the results of DPPH and oxygen radical absorption capacity assays showed that the ethanolic extract of garlic sprouts exhibited stronger antioxidant activities than the ethanolic extract of raw garlic. In addition, the antioxidant properties of aged garlic were found to be higher than fresh garlic by DPPH, ABTS, FRAP, H2O2 scavenging, and Fe2+ chelating assays. Compared with multi clove garlic extract, single clove garlic extract had a higher amount of phenolic compounds and showed stronger antioxidant activity. Moreover, the antioxidant activity of black garlic increased with thermal treatment, and the highest antioxidant activity was obtained on the 21st day of processing. Also, the increased pressure improved the antioxidant activity of garlic paste. However, the antioxidant activity of “Laba” garlic, a traditional Chinese garlic product, decreased during fermentation.

The aged garlic extract induced the expression of several antioxidant enzymes, such as heme oxygenase-1 and the glutamate-cysteine ligase modifier subunit through the nuclear factor erythrobia-2 related factor 2-antioxidant response element pathway, which protected human endothelial cells against oxidative stress. Garlic saponins were reported to protect mouse-derived C2C12 myoblasts against growth inhibition and DNA damage induced by H2O2, and to scavenge intracellular reactive oxygen species.

In summary, garlic and its active ingredients (such as phenols and saponins) have certain antioxidant effects. Different processing methods also affected the antioxidant activity of garlic. Usually, raw garlic had a stronger antioxidant activity than cooked garlic, and the antioxidant activity of fermented garlic, such as black garlic, was stronger than that of crude garlic. In addition, the cellular experiment showed that the mechanism of antioxidative action of garlic might be involved with the enhancement of antioxidant enzyme activities and the regulation of the Nrf2-ARE pathway.



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