Identification of chemical composition and comparison of antioxidant effects of marigold (Calendula officinalis L.) essential oil with butyl hydroxytoluene in canola oil stability

Oxidation of vegetable oils is a major challenge in the food industry. Canola oil is prone to oxidation because of high unsaturated fatty acids. An effective way to prevent oxidation of oils and fats is addition of antioxidants. However using synthetic antioxidant due to the possibility of toxic and carcinogenic effects is limited. Thus, todays essential oils from aromatic plants have been qualified as natural antioxidants and proposed as potential substitutes of synthetic antioxidants in food products. Marigold (Calendula officinalis L.) from Asteraceae family with significant applications in food and pharmaceutical industries. The main objective of this study was to identifythe chemical composition of flowers essential oil and comparison of antioxidant effects of marigold essential oil with butyl hydroxytoluene in canola oil stability.

This experimental study was conducted in 2019 at Nahavand University. Flowers essential oil was extracted by hydro-distillation technique using clevenger apparatus. The oil was analyzed by capillary GC and GC/MS. The total phenolic content of the essential oil was measured by Folin-ciocalteau method. Antioxidant activity of essential oil was assessed by using diphenyl picrylhydrazyl (DPPH) method and β-carotene/linoleic acid system and compared with synthetic antioxidant butylated hydroxy toluene (BHT). Then the effect of marigold essential oil was added to the non containing antioxidant canola oil at four concentrations (100, 200, 400 and 800 ppm) to determine antioxidant activity. Also an oil sample without antioxidant and two oil samples containing 100 and 200 ppm BHT were prepared.The oils were kept at 60 °C for 35 days and peroxide, thiobarbitoric acid, acid and carbonyl values were measured every 7 day. Experimental data were analyzed using ANOVA by the SPSS version 20 software and mean comparison were done using Duncanchr(chr('39')39chr('39'))s multiple range test.

The major components of flower essential oil were -cadinol (49.52%), -cadinene (15.35%) and Δ-cadinene (8.36%), respectively. The concentration of phenolic compounds in the essential oil was determined and found to be 32.74±0.63 mg as gallic acid per gram of essential oil. The half maximal inhibitory concentration (IC50) of marigold essential oil was 10.36±0.21 μg/ml, while this parameter for BHT 9.14±0.19 μg/ml. Flower essential oil of marigold at the concentration of 800 ppm had better antioxidant activity than the other essential oil concentrations. In addition, it was shown that antioxidant activity was directly correlated with the increase of the essential oil concentration. In the study of antioxidant properties of different concentrations of flower essential oil in canola oil showed that the highest antioxidant activity belonged to the oil sample contained 800 ppm of essential oil, which did not show significant difference with BHT at concentration 100 ppm (p> 0.05).

Marigold essential oil at the concentration of 800 ppm has antioxidant acivity in canola oil, it can be concluded that this plant can be a suitable natural antioxidant as an alternative to synthetic antioxidants in the oil industry.