Evaluation of the effects of peppermint essential oil (Mentha piperita) on oxidative stability of soybean oil

The synthetic antioxidants, which have many side effects on human health, are commonly used to control the oxidative stability of oils. So today, researches on essential oil of herbal plant as a safe alternative method are in progress. The aim of this study was application of essential oil of peppermint (PMEOs) herbalplant (as a natural antioxidant) to improve the oxidative stability of soybean oil.

In this study, the quality properties of soybean oil were evaluated after the addition of natural antioxidant of peppermint essential oil (Mentha piperita) with peroxide index, induction period, acidic number, thyobarbituric acid index and oxidative stability index during storage period (for 45 days). For this purpose, by using the response surface method (RSM), the optimum concentration of essential oil was determined with respect to the peroxide index and the induction period factors (by the accelerated shelf life test at 60oC). Then, PMEOs antioxidant was added to soybean oil at optimum concentration and the noted quality properties were compared during the storage period with the blank sample. Also, obtained results from this study were repeated with a sample of soybean oil containing BHT synthetic antioxidant. Moreover, in this research, the factorial experiment in a completely randomizes design was used to analyse the data of the storage stage. Mean comparison of data was carried out by least significant difference test (LSD) in confidence level of 99%.

Gas chromatography-mass spectroscopy (GC-MS) test was used to confirm of the PMEOs. Based on the results, totally 37 components were identified in essential oil of this herbal plant. The main components of the essential oil of this herb plant include iso-Menthol (34.58%), Menthol (29.81%), 1,8-Cineole (5.93%), Menthofuran (4.49%), iso-Menthone (3.51%), Menthol (3.4%), cis-Sabinene hydrate (2.31%) and D-Limonene (1.81%). The results of this research indicated that variation trend of peroxide index, acidic number and tiobarbitoric acid index increased during storage from 1st to 45th day, whereas the induction period of soybean oil showed a decreasing trend. Also, the result of this research indicated that blended of PMEOs (or BHT) could be reduce peroxide index, acidic number and tiobarbitoric acid index than blank sample to 37.57% (35.49%), 54.24% (48.3%) and 15.45% (2.44%) during 45 day storage. Furthermore, the PMEOs (or BHT) than blank sample increased induction period to 13.53% (37.44%) during 45 day storage.

Generally, the results of this study showed that PMEOs (with concentration of 871 ppm) as a natural antioxidant could be improve the quality properties of soybean oil.