Evaluation of the effect of essential oil of Rosemary on sunflower oil, soybean oil and tallow fat

Abstract The oils undergo qualitative changes, especially oxidation due to prolonged exposure to high temperatures and storage, as well as due to the presence of oxygen in the environment. Antioxidants is used as one way to protect the oil from oxidation. Most of the antioxidants that used in the food industry are synthetic and harmful to health. Therefore, studies on the use of natural antioxidants as a substitute for synthetic antioxidants are of high importance. Todays, essential oils are volatile oils and secondary products of plants that are used as a natural antioxidant in oil based foods due to the well-known toxic effects of synthetic antioxidants. In this research rosemary essential oil (extracted (by Clevenger) and commercial) as a natural antioxidant was added to sunflower oil, soybean oil and tallow fat in concentrations of 0.05. 0.1, 0.2 and 5.0%. Fatty acid composition, iodine value, peroxide value, induction period and saponification value were investigated. Also, identification of essential oils was performed by spectrophotometric and gas chromatography methods. Antioxidant activity of essential oils were determined by DPPH method. The results showed that the amount of active compounds in commercial samples (69.69%) was higher than those of extraction sample (52.35%) and it scavenge more DPPH radical than commercial type. Linoleic acid was the predominant fatty acid in soybean and sunflower oils but in tallow oleic acid was found in the highest amount. There is a direct relationship between the amount of effective compounds and the antioxidant activity of the essential oil. The antioxidant activity of the two essential oils, measured by the DPPH radical control method, also indicated that the commercial essential oil had a higher antioxidant activity. Increasing the essential oil concentration increased oxidative stability in the samples, and it increased with increasing essential oil concentration, so that the highest stability was observed in the concentration of 0.5% essential oil. The results showed an increase in the amount of peroxide value during the maintenance period, which was lower with an increased in essential oil content. Iodine and saponification value of samples also showed a decreasing trend with increasing concentrations. In all the experiments the commercial essential oil has done more favorable. The results of this research indicate that there is a direct relation between antioxidant essentials activity and the amount of recognized active compounds. Antioxidant essentials trading activity which measured by DPPH radical control method indicated more activity. According to the results obtained in this study, the use of rosemary essential oils to enhance the shelf life and storage of oil is recommended. Keywords: sunflower, oxidative stability, rosemary, Tallow, soya beans