Effects of black cumin (Nigella sativa) oil on oxidative stability of sunflower oil

Cold pressed black cumin oil (C100) with the proportion of 5 (AC5), 10 (AC10) and 20 (AC20)% was added into the sunflower oil to enhance the stability of the sunflower oil. During the oxidation process, three different conditions as regards high temperature, moderate temperature and ambient temperature (17.7-29.0 °C) were performed. In the high-temperature process, induction periods were determined at 110 °C by means of Rancimat method. The lowest induction period value was found to be 4.73 h for the black cumin oil whereas the induction period of 5.76 h was determined to be the highest value for the sunflower oil. As for the moderate temperature process, oxidation peroxide value and specific absorption value (K232 and K270) are detected in the oven test at 60°C. At the end of 16 days of storage, the peroxide value of the sunflower oil reached to 440.72 meq O2 /kg while that of black cumin oil attained the value of 117.78 meq O2 /kg. Moreover, the peroxide values for 5% (AC5), 10% (AC10) and 20% (AC20) oils were found to be 346.16 meq O2/kg, 310.58 meq O2/kg and 282.01 meq O2/kg, respectively. At the end of the storage, the K232 values were recorded as 69.22 and 17.71 for the sunflower and black cumin oil, respectively. Besides, it was detected that the K232 value is 56.72 for the blended oil produced by the lowest black cumin oil whereas the blended oil prepared by the highest black cumin oil obtains the value of 46.70. On the other hand, the K270 values were determined to be 4.69 for the sunflower oil and 1.88 for the black cumin oil while the values were obtained to be in a range of 3.54 (AC20)-4.47 (AC10) for the blended oils. Volatile oxidation products except for the experimental findings of K232 and K270 values were also determined along with the oven test. Among the components, the maximum rates belong to hexanal and E-2-heptenal. Furthermore, at the end of 6 months of storage in the ambient temperature process, the peroxide values were recorded as 166.16 for the sunflower oil and 33.08 meq O2/kg for the black cumin oil. As for the blended oils, the values were observed to be 136.74 for AC5, 112.88 for AC10 and 93.23 for AC20 meq O2/kg, respectively. At the same time, the K232 and K270 values of the sunflower oil were found to be 27.77 and 3.22 while the values were obtained to be 3.76 and 1.09 for the black cumin oil, respectively. Besides, the values of the blended oils were determined to be 15.86, 2.89 (AC20); 19.75, 3.27 (AC10); 24.04, 3.28 (AC5). Hexanal from the volatile oxidation products was also appeared at the end of storage. During the storage, the hexanal value of all the oils studied was found to be close to each other.