Investigation on the chemical composition, bioactive functional groups, antioxidant potential and cell toxicity (HT29) of Shirazi thyme essential oil: A study in laboratory scale

Shirazi thyme is a perennial herbaceous plant related to Lamiaceae family growing in central and southern regions of Iran. This study aimed to assess chemical composition, bioactive functional groups, antioxidant potential, total phenol, and total flavonoids of Shirazi thyme essential oil (STEO) and also to evaluate its cell toxicity effect against the colorectal cancer cell line (HT29).
 
The chemical composition of STEO was identified by gas chromatography-mass spectrometry. The bioactive functional groups of STEO were measured by Fourier transform infrared at spectra range of 500- 4000 cm-1. The total phenol and total flavonoids of STEO were determined by folin- ciocalteu and aluminum chloride colorimetric method, respectively. MMT method was performed to measure the cell toxicity of STEO against the colorectal cancer cell line (HT29). The cells were cultured on DMEM high glucose medium supplemented with 10% fetal bovine serum and penicillin/streptomycin and incubated at 37°C with 95% relative humidity and 5% CO2 concentration. The antioxidant activity of STEO was evaluated by DPPH and ABTS free radicals scavenging assays. Duncan test at 5% probability and SPSS software (version 18) was performed to compare the means of obtained results.
 
Based on GC/MS spectrometry, a total of 29 constituents were identified and quantified in the STEO representing more than 99% of total constituents. Thymol with 39.3% and Carvacrol with 30% were the most constituents of STEO. The other major compound of STEO were Benzene (8.52%), γ-Terpinene (5.27%), and Caryophyllene (2.97%). The presence of peak at a wavelength of 320- 1000 cm-1 demonstrates O-C bound that could be related to organic compounds such as alcohols, carboxylic acids, esters, and ethers. The peaks occurred at spectral range between 2800- 3000 cm-1 (particularly at 2869.6 up to 2960.8 cm-1) are related to the stretching mode of C-H bounds and are mostly associated with alcoholic compounds in the essence. The amount of total phenol and flavonoids of STEO were 64.05 mg gallic acid equivalent/g and 11.68 mg quercetin equivalent/g, respectively. Results obtained from antioxidant activity of STEO with DPPH and ABTS free radicals scavenging showed that by increasing of STEO, the inhibition level of free radicals was enhanced. The inhibition percent of free radicals by using DPPH and ABTS at 1000 ppm concentration were 63.69% and 64.33%, respectively. The cell toxicity results of different STEO concentrations against the cell line HT29 revealed that survival of HT29 cells at 1, 3.125, 6.25, 12.5, 25, 50, 100 and 200 ppm of STEO were 100, 70.15, 61.19, 59.33, 38.83, 25.68, 20.65 and 12.2%. According to the results of this study, as the concentration of STEO increased, its effect on the cell line HT29 enhanced and the cell percentage viability decreased. Some antioxidant activity of STEO could be interrelated to its phenolic compounds. Based on the results of antioxidant activity, the amount of total phenol and flavonoids and the effect of STEO on cell toxicity against the cell line HT29, it seems that the use of STEO is applicable in the pharmaceutical and food industries