Determination of the structure, chemical composition, antioxidant activity and the cytotoxic effect of Turmeric essential oil

Antioxidants by Quenching free radicals and preventing lipid oxidation, retard spoilage, discoloration and rancidity of foods. Due to adverse effects of synthetic antioxidants such as carcinogenicity and liver injury, consumers’ attention toward natural antioxidants are increasing. Turmeric (Curcuma longa) is a medicinal plant frequently used in food industry and pharmacology. In this research, chemical composition, structure and type of bond, antioxidant capacity, total phenol, flavonoid and cytotoxic effect of Turmeric essential oil (TEO) on colorectal cancer cells (HT29) were investigated.  

TEO was extracted using Clevenger apparatus by aqueous distillation method. To identify chemical composition, 1 µl essential oil was injected in gas chromatography-mass spectrometry and essential oil composition and quantity were determined by comparing with standards. Functional groups and qualitative identification of turmeric essential oil were done using Fourier-transform infrared spectroscopy (FTIR) in range of 500 – 4000 cm-1. Antioxidant capacity of TEO was determined suing ABTS, DPPH and β-carotene/linoleic acid bleaching assay. Total phenol and flavonoid were measured by colorimetric methods. MTT test was used to find cytotoxic concentrations of TEO on colorectal cancer cell line (HT29).  

The 18 compounds identified in TEO accounted for 97.91% and the highest compound was turmerone by 40%. The other compounds were curlone, zingiberene and benzene with 34, 8.30 and 4.18% respectively. Infrared spectrum in range of 3600-3400 cm-1 (specially 3516 cm-1) and peaks at 2930, 1621, 1515 and 1447 cm-1 were due to stretching vibration of O-H, C-H, C=O, C=C bonds of aromatic ring and aromatic groups of curcuminoids. 1515 cm-1 peak was due to stretching vibration of C=O bond of sesquiterpenes (turmerone). Observed peaks at 1378 and 1308 cm-1 confirmed the presence of alkanes or bending vibrations of CH3 groups in curcuminoids (curcumin). Antioxidant potential of TEO according to DPPH and ABTS methods and β-carotene bleaching assay was 25.15, 93.90 and 72.76 %, respectively. Total phenol and flavonoid content of TEO were 38.91 mg GAE/g and 87.9 mg QE/g. The results showed that by increasing essential oil concentration from 3.125 to 200 mg/mL survival rate of HT29 changed from 66.76 to 9.88%.