Description
Botany
Society Garlic is a clump-forming herbaceous perennial, 60 cm high by 60 wide (Plates 1 and 2 ). Its rootstock is an ovoid corm with rhizomatous base, 1.5–2.7 cm long and 1–1.5 cm in diameter. Leaves 8–10, greyish-green, linear, 17–50 cm long, 0.35–0.7 cm wide; apex obtuse; base sheathing grows straight up out of the corm. Scape 39–70 cm long grows up from the centre of the rosette of leaves. Atop the scape sits a large umbel with 8–20 sweet-scented lilac-pink flowers on; pedicels 10–20 mm long arise from the same point (Plates 2 and 3 ). Flower with a cylindrical perianth tube, 8–10 mm long expanding to six elliptic lobes 6–7 mm long, 1.5–2.8 mm wide, apex acute with slightly in-rolled margin. Corona of three distinct oblong lobes, 2.5–3 mm long, 1–1.5 mm wide with retuse apex; stamens included in perianth tube, upper series 2–2.5 mm below mouth, lower series ±6 mm from base; anthers 1 mm long; ovary oblong to obovoid, 2.5 mm long, 1.5 mm in diameter; ovules numerous; style 1 mm long, 0.4 mm in diameter; stigma capitate, small. The fruit, triangular capsules, are grouped into a head, and when ripe, they split to release the flattened, hard black seeds.
Nutritive/Medicinal Properties
Jacobsen et al. ( 1968 ) reported the presence of an alkylcysteine sulfoxide lyase and three unidenti-fi ed S-substituted cysteine sulfoxide deriva-tives, whereas Burton and Kaye ( 1992 ) isolated 2,4,5,7-tetrathiaoctane-2,2-dioxide and 2,4,5,7-tetrathiaoctane from the leaves of T. viola-cea . The amino acid (RSRC)- S -(methylthiomethyl) cysteine-4-oxide was isolated from rhizomes of Tulbaghia violacea (Kubek et al. 2002 ). Its con-tent varied in different parts of the plant (rhi-zomes, leaves and stems) between 0.12 and 0.24 mg/g fresh weight, being almost equal in the stems and rhizomes. In addition, S -methyl- and S -ethylcysteine derivatives have been detected in minute amounts (<3 μg/g fresh wt) in all parts of the plant. 2,4,5,7-Tetrathiaoctane-4- oxide, the primary breakdown product of the amino acid, was also detected and isolated.
Scientific studies have shown that Society Garlic possesses several biological activities which include antioxidant, antimicrobial, anti-cancer, antiulcerogenic, antithrombotic and anti-hypertensive properties.
Antioxidant Activity
The antioxidant capacity (oxygen radical absor-bance capacity, ORAC value) and total phenolic content for Society Garlic, Tulbaghia violacea , was determined as 1.03 μmol of Trolox equiva-lents (TE)/g of fresh weight, 7.50 mg of gallic acid equivalents (GAE)/g of fresh weight respec-tively (Zheng and Wang 2001 ).
Antihypertensive Activity
Tulbaghia violacea was one of the many active plants with antihypertensive properties as deter-mined by the angiotensin-converting enzyme (ACE) inhibition assay; it contained no tannin (Duncan et al. 1999 ). T . violacea leaves had inhibi-tion levels which were above 50 % (aqueous extract gave 72 % inhibition, ethanol extract exhibited 61 % inhibition), while T. violacea roots gave 49 and 27 % inhibition for aqueous and ethanol extracts, respectively, with 25 μg plant extract. This was also confi rmed in a recent study. A plant was considered to have potential antihypertensive prop-erties if it inhibited the angiotensin-converting enzyme (ACE) and thus the conversion of angio-tensin I to angiotensin II by greater than 50 %, and T. violacea was one of eight of 16 plants screened that demonstrated ACE inhibitory activity and sat-isfi ed these criteria (Ramesar et al. 2008 ). T. viola-cea in particular showed promise with regard to ACE inhibition as in-vivo administration of this extract showed only a 2.2 % increase in maximum mean arterial pressure when compared to the 14.5 % increase observed in the control group after coadministration with exogenous angioten-sin I. Hypertension is treated with medication, including drugs such as angiotensin-converting enzyme inhibitors (ACEI) and angiotensin II receptor blockers (ARB). These drugs not only lower blood pressure but also offer additional protection to the brain and heart. ACEI, in partic-ular, provides benefi cial properties to patients with type 1 diabetes.
The methanol leaf extract of Tulbaghia violacea signifi cantly and dose-dependently reduced the systolic, diastolic, and mean arterial blood pressure and heart rate in male spontane-ously hypertensive Wistar rats (Raji et al. 2012 ). Angiotensin I human acetate salt hydrate (ang I, 3.1–100 μg/kg), angiotensin II human (ang II, 3.1–50 μg/kg), phenylephrine hydrochloride (phenylephrine, 0.01–0.16 mg/kg) and dobuta-mine hydrochloride (dobutamine, 0.2–10.0 μg/kg) all increased the blood pressure dose- dependently. The hypertensive effect of ang I and the heart rate-increasing effect of dobutamine were signifi cantly decreased by their co-infusion with T. violacea (60 mg/kg). However, the co- infusion of ang II or phenylephrine with T. viola-cea (60 mg/kg) did not produce any signifi cant change in blood pressure or heart rate when com-pared to the infusion of either agent alone in the same animal. The reduction in blood pressure may be due to actions of the T. violacea methanol leaf extract on the angiotensin-I-converting enzyme (ACE) and β(1) adrenoceptors.