Ajoene Studies

1.   Antioxidant Functions of E- and Z-Ajoene Derived from Japanese Garlic (Naznin et al, 2010)

The antioxidant activities in Allium sativum have been of particular interest because of the relationship between oxidative stress and pathologies such as atherosclerosis, cancer, and aging, in which free radicals and reactive oxygen species are implicated. Many recent studies on antioxidant activities use crude extract of Allium species and many investigators have insinuated that the thiosulfinates or related organosulfur components are primarily responsible for the observed antioxidant effects. Pure alliin has no antioxidant activity in a linoleic acid emulsion, despite earlier claims that alliin is an effective antioxidant. Allicin, diallyl disulfide and diallyl trisulfide have been studied extensively for the antioxidant activities. Until 2010, no study has been undertaken to study the antioxidant activity of ajoene. The purpose of this study was to examine the antioxidant property of E– and Z-ajoene derived from Japanese garlic.
Ajoene was extracted according to the method developed earlier (Naznin et al, 2007) and E-ajoene and Z-ajoene were separated with silica gel column chromatography. In vitro antioxidant activities of both isomers of ajoene on DPPH radical, hydroxyl radical, superoxide anion and H2O2 were analysed. For DPPH radical scavenging assay, antioxidant activity of ajoene was measured in terms of hydrogen donating or radical scavenging ability, using the stable radical DPPH. The scavenging activity of the hydroxyl radical was measured using the deoxyribose method with slight modification. The ability of E– and Z-ajoene to scavenge superoxide anion was determined on the basis of inhibiting the reduction of nitro blue tetrazolium. Lastly, the ability of ajoene to reduce H2O2 with Fe3+-xylenol orange (FOX) complex assay was measured. The statistical analysis of the measured parameters was made using the analysis of variance (ANOVA).

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Figure 1 Antioxidant activity of 1mM E– and Z-ajoene.

This study demonstrated that E– and Z-ajoene have various extents of antioxidant properties, including scavenging activities for DPPH radicals and hydroxyl radicals.

In general, antioxidant activities shown in this study suggest that E– and Z-ajoene may be used as a source of antioxidants.

2.   Inhibition of Microbial Growth by Ajoene, a Sulfur-containing Compound Derived from Garlic (Naganawa et al, 1996)

Various antibiotic effects of ajoene have been reported. Antifungal activity of ajoene had been shown against A. niger, C. albicans, and P. brasiliensis. Weber et al and Tatarintsev et al had also demonstrated antiviral activity of ajoene. However, antimicrobial activity of ajoene had been demonstrated only for one yeast species and two fungus species hitherto (1996); therefore, antimicrobial activity of ajoene for bacteria and some species of yeast were examined.
Preparation and isolation of ajoene were carried out according to the method described by Block et al (1986). Minimum inhibitory concentrations (MICs), the lowest concentration of an antimicrobial that will inhibit the visible growth of a microorganism after overnight incubation and minimum microbicidal concentration (MMCs), which is the minimum concentration required to kill the cells were examined. Antimicrobial property of ajoene against B. cereus and C. albicans was also tested against diallyl sulfide (DAS), diallyl disulfide (DADS) and sorbic acid (a known food preservative). 

Table 2.MIC and MMC of ajoene for organisms in this study (extracted from Naganawa et al, 1996)

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Table 3. Comparison of the antimicrobial activities for B. cereus and C. albicans (extracted from Naganawa et al, 1996)

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The MICs of ajoene for each microorganism are shown in Table 2. Generally ajoene showed strong inhibition against most gram-positive bacteria such as Bacillus spp., S. aureus, Mycobacterium spp., L. plantarum, and S. griseus. The MICs against yeast were about 20 µg ajoene per ml, whereas against gram-negative bacteria, the MICs were a little bit higher, such as E. coli (116 µg/ml) and P. aeruginosa (>500µg/ml). The antimicrobial activities of ajoene, DAS, and DADS as derivatives of allicin and sorbic acid as a food preservative were compared by addition at various concentrations to culture broth of B. cereus and C. albicans. Overall, ajoene showed a strong antimicrobial effect even at a concentration of 10 µg/ml.