application of satureja hortensis l. and zataria multiflora boiss. essential oils as two natural antioxidants in soybean oil during microwave heating

background: autoxidation is considered to be the main route of edible oil deterioration, which produces undesirable odors and flavors during storage and heating. the unpleasant flavor of oxidized oil has been attributed to primary and secondary products of unsaturated fatty acids. the microwave heating is a rapid method when compared with other methods of heating. objective: in this research, the effect of microwave heating on the oxidative stability of soybean oil amended with either of satureja hortensis l. (sheo) and zataria multiflora boiss (zmeo) essential oils was evaluated and compared with synthetic antioxidant (butylated hydroxyl toluene= bht 200 ppm). methods: soybean oil containing with sheo (200 and 1000 ppm), zmeo (200 and 1000 ppm) and bht (200 ppm) were heated using microwave oven (600 w) for 25 min and spectrophotometer was used to determine uv absorption. peroxide value (pv), conjugated dienes (cd) and conjugated trienes (ct) indices were measured. results: statistical results showed that pv after 25 min were increased in all treatments and the stability of soybean oil treated with synthetic antioxidant (bht, 200 ppm) was higher than oil treated with the studied essential oils (sheo and zmeo, 200 and 1000 ppm). diene and triene indices increased during the heating. there was a positive correlation between pv, diene and triene indices during the process of microwave heating. conclusion: the two essential oils (sheo and zmeo, in concentrations of 200 and 1000 ppm) showed fairly good antioxidant activities as compared with bht (200 ppm) in soybean oil control sample (refined- bleached- deodorized soybean oil without any additives).