بررسی رابطه بین ترکیب اسیدهای چرب با پایداری روغن در مخلوط روغن های آفتابگردان وکانولا

Low stability in vegetable oils has been a quality problem. On the other hand the stability of vegetable oils depends on the composition of fatty acids especially oleic and linoleic acids. The aim of this study is finding one or more optimum ratio of the mixture of sunflower and canola oils that have good stability as well as suitable amount of essential fatty acids. The other aim is survey of dependence of stability to the amount of fatty acids in the mixture of sunflower and canola oils. In this study 7 samples of deodorized (and without any synthetic antioxidant) oils were prepared from several ratios of sunflower and canola mixtures. Metrohm rancimat was employed to evaluate the stability of the samples at 110°c. Fatty acids composition was determined with GC and peroxide ,iodine value and refractive index at 40◦c be measured. There was a strong straight linear correlation between stability and the amount of oleic acid ( r=0.988 , P-Value=0) but there was a straight reverse correlation between stability and the amount of linoleic acid ( r= -0.988 , P-Value=0). Results showed that the canola oil in spite of its higher linolenic acid, had higher stability than sunflower oil. Between the amount of canola oil in mixture (with sunflower oil) and iodine value (r=-1, P-Value=0) and refractive index (r=-1, P-Value=0) there were reverse correlation. Results demonstrated that sunflower oil, in spite of its lower linolenic acid, had very lower stability than canola oil. The reason may be that sunflower oil has high content of linoleic acid, while canola oil has high content of oleic acid. With the considering the results, it is recommended that canola oil can be added to sunflower oil to increase its stability and nutritional values. Moreover two formulas "70% canola oil+ 30% sunflower oil" and "50% canola oil+ 50% sunflower oil" proposed as suitable blends.