Abstract
This study identified and characterized two herbs that grow in the wild in Kurdistan-Iraq, namely Thymus syriacus var. Syriacus and Thymbra spicata L. Thyme and thymbra shade-dried leaves were extracted by hydrodistillation; it was found that the herbal volatile oil (VO) yields were significantly higher (P < 0.05) in whole leaves compared with ground leaves. The average VO content in whole Thymus syriacus and Thymbra spicata at high altitude was 3.75±0.1% (v/w) and 4.15±0.15% (v/w), and at low altitude VO values were 2.52±0.12% and 2.2±0.08%, respectively. GC and GC-MS characterization showed that thyme comprised mainly 74.1% thymol and 9.0% carvacrol whereas thymbra comprised 74.0% carvacrol and 10.7% γ terpinene. Thyme and thymbra (VOs), thymol and carvacrol (0.5 and 1.0%) showed significant antioxidant activities in UV-oxidised sunflower oil using iodometric titration and ferrous thiocyanite (FTC) methods for peroxide values measurement and thiobarbituric acid related substances method for secondary products. The herbal VOs (at 0.25, 0.5, 1 and 2 μM), thymol and carvacrol (0.025, 0.05, 0.1 and 0.25 μM) exhibited significant inhibition in Cu++ induced low density lipoprotein (LDL) oxidation. Amongst the other seven terpenoids used in this study, γ terpinene (0.25, 0.5, 1 and 2 μM) showed the strongest antioxidant activity including its isomer a terpinene. Thyme and thymbra VOs and their individual components were evaluated for their antimicrobial activities against a range of microorganisms. The VOs, thymol and carvacrol exhibited zone inhibition using a disc diffusion method. The VOs were evaluated against E. coli in nutrient broth and showed minimum inhibitory concentration (MIC) of 0.015 and 0.02% and minimum cidal concentration (MCC) of 0.02 and 0.025% for thyme and thymbra respectively. The VOs showed MIC (0.05%) and MCC (0.1%) in skimmed milk, but they showed no effect in whole milk even at 0.5%. Thyme and thymbra VOs (0.1, 0.25 and 0.5 uM), thymol and carvacrol (10, 20, 50 and 100 μM) showed no toxicity when incubated with Caco-2 and endothkelial cell lines using the MTT method. The VOs and the terpenoids exhibited significant antioxidant activity against oxidative stress by tert-butyl hydroperoxide (t-BHP) on cell proliferation. In conclusion thyme and thymbra VOs may have significant applications in food preservation as antioxidants and antimicrobials and in the inhibition of LDL oxidation in vitro as they are safe to be used at 0.25 - 2.0 μM concentrations.