**4. Garlic (***Allium sativum)*

Garlic (Fam. Liliaceae) is widely distributed and grown around the world (**Figure 5**). It is considered to be a valuable preventive remedy, folk food and spice. As the primary antidote to an epidemic, garlic has been used as a remedy throughout history for typhus, dysentery, cholera and influenza [45].

Garlic has long been appreciated by physicians from different nations as a remedy in the ancient and Middle Ages as well as during the modern period [46]. Garlic has been used as a remedy in ancient China since 2700 BC. The ancient Indians used garlic as a tonic, to treat cases of lack of appetite, skin problems, rheumatism, hemorrhoids, and more. In addition to being known as Russian penicillin, garlic was also used for years as a remedy for children with respiratory tract diseases via inhalation [47].

#### **4.1 Phytochemistry**

Garlic contains various sulfur compounds, vitamins (A, B1), enzymes and minerals (germanium, calcium, copper, iron, potassium, magnesium, and selenium). Total 17 amino acids are found in garlic, and major are glutamine, glycine, lysine, cysteine, valine, methionine, isoleucine, leucine, tryptophan, and phenylalanine [48].

The pungent odor of garlic and many of its therapeutic effects are caused by the high levels of sulfur compounds present in this species of Allium. Allicin (diallyl thiosulfinate or diallyldisulfide) is a highly biologically active compound in garlic (**Figure 6**) [49]. In fresh and dry garlic, alliin (S-allyl cysteine sulfoxide) is the compound producing the highest levels of sulfur. Garlic is commonly prepared by cutting, mincing, crushing, which disturbs S-allyl cysteine sulfoxide and exposes it to the allinase enzymes, which then convert it into diallyl thiosulfinate, the aromatic constituent [48]. Below a pH of 3.5 or upon heating, the allinase enzyme responsible for diallyl thiosulfate conversion becomes inactive. Recent studies have shown that other compounds may play a greater role in anti-oxidant function than allicin [50].

**Figure 5.** *Garlic.*

*Vegetable and Herbal Extracts: A Way towards Preventive and Therapeutics Regimen DOI: http://dx.doi.org/10.5772/intechopen.101104*

**Figure 6.** *Allicin.*

## **4.2 Medicinal and nutritional value**

There have been several studies showing possible cancer-preventive effects of garlic preparations and their constituents in vitro and in vivo. In garlic, a number of potent anticancer compounds have been found, including allylsulfide derivatives. Different garlic derivatives are shown to modulate various cellular mechanisms for promoting cancer, such as DNA adduct formation, mutagenesis, and free radical scavenging. They may also contribute to angiogenesis [46]. A number of studies have concluded that garlic protects liver cells from some toxic compounds [49].

Organosulfur compounds derived from garlic are known to inhibit cancer in various animal models by modifying cytochrome P450 which is responsible for the activation of nitrosamines, hydrazine and benzene [51]. The chemical present in garlic extract diallyl sulfide and its oxidation products diallyl sulfoxide and diallyl sulfone inhibit chemical carcinogenesis and mutagenesis [52]. These compounds restrict development of chemically induced cancers by blocking the phase-1 enzymes. These organo sulfur compounds also induce phase-2 enzymes such as glutathione S-transferase, quinone reductase and glucuronate transferase which eventually regulate removal of toxic compounds. Garlic extract is also known to modify -SH containing enzymes and increases their activity via formation of disulfide bond between protein thiol and thiol group of cysteine [53]. This type pf bond formation with proteins is an effective redox method to regulate protein activity.
