Evaluation of antioxidant effect of oregano (Origanum Vulgare) essence on oxidative stability of frying oil

Introduction: The oxidation of fats and oils during food processing and storage not only causes loss of nutritional and digestive quality, but also produces compounds such as free radicals that lead to potentially biologically adverse and chemical reactions, Therefore, the use of antioxidants is essential to prevent the onset of corruption. Although many oils contain natural antioxidants such as flavonoids and tocopherols, due to insufficient efficacy of these compounds, they should be added to edible oils (Ibrahimzadeh et al. 2008). Synthetic antioxidants such as butylated hydroxy anisole (BHA), butylated hydroxy toluene (BHT), and tertiary butylated hydroquinone (TBHQ) are commonly used to delay the oxidation spoilage of oils (Semnani et al. 2006). extraction and purification of rosemary extract and its extensive supply for nutrition and hygiene as a natural antioxidant (sunjae et al. 2011) or extract of iranian oregano extract and evaluation of antioxidant activity and competition with BHT synthetic antioxidant in sunflower oil there have been some of these efforts (kamkar et al. 2010). Other plant sources that have been studied in recent years for antioxidant compounds in their essential oils or extracts can be found in Laurus nobilis (Inan et al., 2012), Citrus aurantium (Saro et al. 2013), Pulicaria  gnaphalodes (Kamkar et al. 2013), lavender (Tahanjad et al. 2010) and Malva sylvestris (Tahanjad et al. 2012) were noted.In order to investigate the antioxidant potential of the active ingredients in aromatic plants, the present study evaluated the antioxidant properties of the essential oil of Oregano in comparison with the synthetic antioxidant of TBHQ in frying oil stability.
Material and methods: Oregano was collected from the area around Shooshtar in Khuzestan province in mid-autumn and after wash and rinse to remove dust, it was dried at laboratory (temperature 28 ° C and 44% relative humidity) and then 100 g of The dried plant was transferred to a Clevenger apparatus and extracted for 3 hours and then dehydrated with sodium sulfate and stored at 4 ° C. Compounds of extracted essential oil by injection of 0.5 μl Cyclohexane diluted essential oil to Agilent 6890A gas chromatograph containing HP-5 column (30 m length, 250 μm internal diameter and 0.25 μm constant phase thickness) attached to Agilent 59 mass spectrometer is identified. Total phenol content of the essential oil was determined by Folin-Ciocalteu method and its antioxidant activity by DPPH and ABTS tests. Antioxidant activity of oregano essential oil at three levels of 200, 500 and 1000 ppm and TBHQ synthetic antioxidant at 200 ppm in antioxidant-free frying oil (consisting of 60% soybean oil, 40% palm and 100 ppm citric acid) at 90 ° C on days 0, 1, 2, 3, 4, 5 and 6 were evaluated by measuring peroxide value and thiobarbituric acid test.
Results and discussion: Based on the results, twenty-two compounds were identified by water distillation. It contained 95.3% of the essential oil. Of these, polygon (31.54%), cineol 1-8 (15.88%), menthofuran (11.8%) and cis iso-polygon (9.74%) constituted the major constituents of the plant essential oil. The results of this study were somewhat different from those of others. The differences in the type of essential compounds and their percentages in the essential oils can be attributed to differences in climatic and plant growth, harvest time, shelf life, method of extraction, and finally genetic variation of the plant. Each gram of oregano essential oil contained 7.5 mg phenolic compounds based on gallic acid on dry matter. There was a direct relationship between the essential oil concentration and its DPPH scavenging effect. The EC50 index of oregano essential oil was 1 mg / ml. Radical inhibitory power of oregano essential oil was compared with synthetic antioxidant TBHQ and the results showed that oregano essential oil at a concentration of 1 mg / ml had inhibitory power equivalent to 0.06 mg / ml of TBHQ antioxidant. Based on the results and comparison of EC50 essential oil with those investigated by other researchers, it is clear that the essential oil has good antioxidant activity and has good antioxidant activity compared to other antioxidant sources. There was a direct relationship between the essential oil concentration and ABTS radical scavenging ability. Evaluation of antioxidant activity of essential oil in fried oil for 6 days at 90 ° C in terms of peroxide and thiobarbituric acid values showed that Peroxide value was dependent on the concentration of treatments and decreased with increasing concentration of treatments and hence there was a significant difference (P<0.05). On the other hand, no significant difference was observed between the concentrations of 500 and 1000 ppm (P<0.05). In the first days of the test, concentrations of 500 and 1000 ppm of Oregano essential oil and TBHQ antioxidant reduced the same amount of peroxide but were weaker than TBHQ antioxidant on day 4 and reduced peroxide to a lesser extent. The concentration of 200 ppm essential oil from day 4 did not show any significant difference with control. Concentration of 500 ppm of Oregano Essential Oil during the Test with TBHQ Antioxidant Reduced Thiobarbituric Acid. The results of this study showed that Oregano essential oil has high potency in inhibiting DPPH and ABTS radicals and in terms of changes in peroxide and thiobarbituric acid during storage under oxidation conditions and the effect of essential oil concentrations in comparison with synthetic antioxidants. The results of this study indicated that oregano essential oil can be used as a replacement for synthetic antioxidants in oil and in addition to eliminating synthetic antioxidants, which can cause cancer by accumulating in tissues and organs, enhancing the thermal stability of the oil without causing undesirable changes.
Conclusion: Different concentrations of oregano essential oil showed antioxidant activity and decreased oxidation rate. Volatile compounds, although they play the most important organoleptic role in oils, have a negative effect on the sensory properties of the product during frying and over time, possibly due to oxidation and formation of substances. It produces a bad taste and smell. Also, because of its ability to react with oxidation-induced radicals, this essential oil can be used as a natural antioxidant in food products, especially fatty foods and prolong their shelf life. In addition, natural antioxidants are safe and beneficial to the consumer