Oxidative Stability of Sesame Ardeh Oil Enriched with Melissa officinalis Essential Oil at High Temperature and During Storage

Vegetable oils such as sesame oil contain a high percentage of unsaturated fatty acids and prone to oxidation and production of highly toxic metabolites. Antioxidants are compounds that inhibit or delay the process of food oxidation. Synthetic antioxidants have been commonly used in the food industry, but there has always been debate about their quality and safety. On the other hand, the use of natural antioxidant compounds such as medicinal plants derivatives are increasing. Lemon balm is known as a medicinal plant that contain various constituents with different properties such as strong antioxidant activity. This study was carried out to investigate the antioxidant effect of different concentrations of Melissa officinalis essential oil against oxidation of sesame Ardeh oil at 60 °C during storage.

Melissa officinalis essential oil was extracted and GC-MS analysis was used to calculate the composition of the essential oil. Then, The total phenolic content of oils was measured using the Folin–Ciocalteau method. In this study, the concentrations of 0, 500, 1000 and 2000 PPM of the essential oil were added into the sesame Ardeh oil. Also, TBHQ as synthetic antioxidant was used as positive control group with concentration of 200 PPM. scavenging activity was assessed by evaluation of DPPH free radical scavenging activity. Rancimat assay was also used to calculate the induction period of the volatile compounds production. Then, the antioxidant effect of essential oil in different groups were evaluated on days 1, 5, 15, 25 and 35 after adding essential oil to the sesame Ardeh oil by measuring the peroxide (PV) and thiobarbituric acid index (TBA).

The results of GC/MS analysis showed that Neral and Geranial compounds had the highest concentration in Lemon balm essential oil. the highest DPPH free radical scavenging activity was observed in the groups receiving TBHQ and 2000 PPM essential oil about 61.6 and 50.2 percent respectively. The induction period index (IP) of the groups containing TBHQ, 2000 and 0 PPM essential oil were calculated to be 11, 9.4 and 6.2 hours. Moreover, at the end of study peroxide value of the TBHQ and 2000 PPM groups were obtained 13.4 and 14.1 (mEq/Kg) respectively and thiobarbituric acid index at these groups were shown to be 1.1 and 1.5 (μmol/gr). Also there was a direct relationship between the essential oil concentration and antioxidant activity indexes. However, the parameters were increased in all experimental groups during storage.

The findings of the present study showed that the lemon balm essential oil is a rich source of antioxidants substances such as neral and geraniol and could increase the stability of sesame Ardeh oil in which exposed to the high temperatures during time storage in such a way that oxidation inhibitory activity of essential oils at high concentrations was calculated to be 74-85% of TBHQ oxidation inhibitory ability. Accordingly, it can be considered as a suitable alternative to synthetic antioxidants.