effect of thermal treatment on chemical changes and oxidative stability of iranian common virgin olive oil of roodbar region: a study on zard, mari and phishomi

the present study attempts to investigate the effect of thermal treatment at 180 °c for 8 hours on chemical changes, quality indexes and oxidative stability of three iranian common virgin olive oils (zard, mari and phishomi). oil samples were taken every 2h of heating treatment and assessed for fatty acid composition, conjugated diene value, carbonyl value, color index and oxidative stability index. prior to the treatment, the total amount of phenolic compounds was also measured. mari oil showed the highest amount of phenolic compounds (p<0/05). during thermal treatment, zard and mari oils exhibited the highest content of the total monounsaturated fatty acids, monounsaturated fatty acids to polyunsaturated fatty acids ratio and oleic acid to linoleic acid ratio. zard and mari oils showed the same trend for conjugated diene value, whereas, after 8 hours of starting heat treatment, the conjugated diene value of phishomi oil increased to the highest level (67.92), compared to samples a and b (46.28 and 47.37, respectively). it was also observed that, mari oil illustrated lesser amounts of carbonyl value and highest of oxidative stability index rather than zard and phishomi oils. the color index of zard and mari oils was lesser than phishomi oil during heating treatment. according to the results of this study, it could be claimed that mari oil had high stability to oxidation during thermal treatment at 180 °c