Scientific Research in School Volume 3 Issue 1 2021
Influence of ultraviolet light on the stability of allicin in aqueous garlic extract James Wilson Barker College Garlic has been recognised and exploited as a medicinal panacea for thousands of years and is widely utilised as a flavouring agent for foods. Since its discovery in 1944, extensive research has been dedicated to investigating the nature and stability of allicin, the primary organosulfur accredited for garlic’s therapeutic properties. However, the extent to allicin’s photostability remains undefined. The present study examines allicin’s potential for photodecomposition by investigating whether exposure to artificial ultraviolet light of wavelength 366 nm in storage affects allicin’s rate of degradation in an aqueous garlic extract. Two aqueous garlic extract samples were stored over a 25 hour period; one exposed to UV of wavelength 366 nm, and the other to darkness as a control. Utilising an established indirect colourimetric assay, the allicin concentration of the two samples was monitored and content loss was analysed using an ANOVA test and PostHoc Tukey HSD. The discovery of significant differences in allicin content loss between the two samples demonstrated that allicin exposed to UV light degraded at a faster rate, thus providing evidence for its susceptibility to photodecomposition. Literature review Garlic (allium sativum) has occupied a prominent position amongst bulb vegetables for millennia due to not only its utility as a condiment, but its exploitable therapeutic potentials (Borlinghaus et al., 2014). Its health benefits have been attributed to the antioxidant activity of a variety of organosulfurous compounds, however in 1944 the sulfur-containing defence molecule allicin (diallyl thiosulfinate) (1) was isolated and accredited as the primary organosulfur of the thirty-three identified compounds responsible for crushed garlic’s pharmacological potentials (Cavallito and Bailey, 1944) (Table 1). Table 1: Types and concentrations of prominent thiosulfinates in garlic extract (After: Herng, 2014)
Thiosulfinate (TS) Allyl-2-propenTS (allicin) (1) AllylmethaneTS trans-1-propenyl-2-propeneTS methyl-2-propeneTS Allyl-trans-1-propeneTS methylmethaneTS trans-1-propenylmethaneTS methyl-trans-1-propeneTS
%mol 50 – 90 3 – 20 5 – 18 1.5 – 8 1.5 – 2 1–2 1–2 0.5
The organosulfur presence within fresh garlic is approximately four times greater (per gram of weight) than that of other food sources such as cruciferous vegetables (Prati et al., 2014), with 1 g of fresh garlic containing between 11 and 35 mg of organosulfurous compounds, of which, allicin constitutes approximately 70% (Mansor et al., 2016). Allicin is not present in raw
garlic, but is produced in an enzymatic reaction catalysed by the crushing of garlic cloves. Upon cell lysis, the odorless non-proteinogenic amino acid alliin, (S-allylcystein sulfoxide) (2) (Figure 1), originally compartmentalised in mesophyll cells, reacts with the enzyme alliinase that is released from the cell vacuoles, thus creating allicin (Prati et al., 2014) (Figure 1). Hence, in vivo and most dietary applications for allicin require the garlic to be in an aqueous extract form. Allicin has been discovered to possess a range of antimicrobial activities that are responsible for crushed garlic’s therapeutic potentials. These antimicrobial properties include antibacterial activity against Gramnegative and Gram-positive bacteria including strains of Escherichia Coli and salmonella, as well as a broad spectrum of bacterial isolates, many of which are resistant to antibiotics (Ankri and Mirelman, 1999). Allicin has also shown antiparasitic activity, including but not limited to in vitro inhibition of the major human intestinal protozoan parasite, Entamoeba histolytica (Mirelman, Monheit and Varon, 1987), which is responsible for 100,000 global deaths per year (Gunther et al., 2011). Additionally, this thiosulfinate demonstrates antifungal activity, particularly against low concentrations of species of Candida, Cryptococcus, Trichophyton, Epidermophyton and Microsporum in vitro, and antiviral activity, with influenza B and herpes simplex viruses showing sensitivity to crushed garlic (Tsai et al., 1985).
Science Extension Journal • 105
