Evaluation of antioxidant activity of Mentha Pulegium (L.) essential oil in Linseed Oil in comparison with synthetic antioxidant

The Oils and fats are considered as one of the most valuable nutrients, rich sources of energy and important precursors in the body's metabolic processes. These compounds play an important role in providing essential fatty acids and fat-soluble nutrients needed by the body. In addition to biological and nutritional role, lipids are important in food processing, determining the quality and organoleptic properties of food products. Edible oils containing high levels of unsaturated fatty acids (especially polyunsaturated fatty acids) are highly susceptible to oxidation. Oxidation of the oil leads to a loss in its organoleptic properties, nutritional value and shelf life, as well as a negative effect on the health of consumers due to the production of undesirable compounds in the oil. Adding antioxidant compounds to refined oils and fats is a common method used by manufacturers to protect these compounds from adverse changes during the storage and processing of food and to extend the shelf life of foods containing lipid compounds. Taking to account the side effects of the synthetic antioxidants, many efforts have been made to identify and extract the antioxidant compounds from plant sources to be used in food and pharmacy as an alternative for synthetic types. Mentha pulegium (L.) plant needs to be further studied in terms of antioxidant activity and phenolic and flavonoid compounds. It is an aromatic plant that grows in many countries and has been considered by various industries, such as food and medicine. This plant is a rich source of natural antioxidants, such as pulegone and other volatile compounds. The aim of this study was to investigate the antioxidant properties of Mentha pulegium (L.) essential oil in Linseed oil in order to select a suitable alternative to synthetic antioxidants such as TBHQ.

In this study, Mentha pulegium (L.) essential oil was extracted by Clevenger (water vapor distillation). Chemical analysis of essential oil by gas chromatography equipped with spectrometer showed approximately 16 different compounds in the essential oil of this plant. Based on the findings obtained from chemical analysis of essential oil, polygon is the most important constituent of essential oil of peppermint plant, which accounts for 51.4%. The obtained essential oil was used in four levels of concentration (0.05%, 0.1%, 0.2% and 0.3%) (w/ w) to observe its effect on delaying oxidation process in Linseed oil. Its oxidant properties were compared with the effect of synthetic antioxidant TBHQ at the concentration level of 0.02% by calculating the determination of acid number and peroxide number during time intervals (zero-7-14-21-28) days. 28) days.

The results indicate that the highest peroxide value of 8.17 (meq/Kg) was related to the control sample on the 28th day and the lowest peroxide value of 3.83 (meq/Kg) was related to the treatment containing TBHQ on the seventh day. Also, the highest acidity value of 2.62 was related to the control sample on the 28th day and the lowest acidity value of 1.88 was related to the TBHQ treatment on the first day. In all treatments of Linseed oil containing Mentha pulegium (L.) essential oil, the resistance time against oxidation was increased with increasing the concentration of essential oil. This indicates that with increasing the concentration of essential oil, the effect of antioxidant compounds in the essential oil in increasing the stability time of flaxseed oil has been increased.In different treatments of Linseed oil on all days, samples containing Mentha pulegium (L.) essential oil with a concentration of 0.3 had the lowest number of peroxide and after those treatments containing 0.2 and 0.1, respectively, showed less resistance to oxidation. The treatment containing TBHQ was less resistant to the oxidation process than these three treatments. Among the treatments, the highest number of peroxides in all days was related to the control sample, which is due to the lack of antioxidants and thus the increase of free radicals in this treatment. The above findings can be inferred from changes in acid number during the experiments.

Since Mentha pulegium (L.) essential oil has unique properties, several applications can be attributed to it; So that this natural effective substance can be a suitable alternative to artificial preservatives due to its role of inhibiting the growth of microorganisms and increasing the shelf life of food products. Also, the essential oils of this plant are considered as powerful antioxidants due to their phenolic compounds, so they can be considered as a suitable alternative to synthetic antioxidants whose adverse effects on humans have been proven. On the other hand, the constituents of this essential oil, which are mainly monoterpenes, have a pleasant aroma, and this aromatic plant can be used in various industries to create the desired natural aroma. According to the results obtained from both acid number and peroxide number tests, Mentha pulegium (L.) oil in high concentrations showed a comparable antioxidant effect with the treatment containing TBHQ and can be considered as a suitable alternative to synthetic antioxidants. Keywords: Essential oil, Antioxidant properties, Mentha pulegium (L.), Linseed oil, TBHQ