One of the most reactions that related with edible oil spoilage is oxidative reactions that cuase undesirable change in taste, smell and texture. On the other hand, consumers are not preferred the desirable taste and smell. Thus, in this research to improve these limitations, production of flavored soy oil by peppermint essential oil was investigated.

 To find the minimal concentration addition of peppermint essential oil to improve oxidation stability (by determining the peroxide and TBA indices, oxidative stability index) and also organoleptical properties of soy oil (taste, smell and overall palatability), central composed design (CCD) with 13 experiments was used. In optimization design, the range of essential oil concentration and storage time were select (up to 8 day) and (0, 900 & 1800 ppm), respectively.

 The results indicated that by increasing oil storage time in the oven (at 60oC) peroxide (p<0.01) and TBA (p<0.05) indices increased relatively and induction period and OSI decreased (p>0.05) that this action corresponding to reduction of organoleptic attributes of the oil. Also, the results showed that addition of essential oil to optimum value (1300 ppm) caused to decreased peroxide (p<0.01) and TBA (p>0.05) indexes and increased of induction period (p>0.05). Furthermore, the addition of essential oil to soybean oil in all concentrations had a positive effect on the perception of organoleptic attributes by panelist.

According to optimization properties, the minimum concentration of essential oil for production of flavored soybean oil was determined equal 1300 ppm. At optimum point (essential oil concentration of 1300 ppm), the values of responses such as peroxide value, TBA index, induction period, OSI, taste, smell and overall palatability were reported 0.034 meq O2/g, 0.023 meq MDA/kg, 7.33 h, 1.029, 9 cm, 8.43 cm and 17.43 cm, respectively.