Thermal stability of corn oil flavoured with Thymus capitatus under heating and deep-frying conditions

BACKGROUND: The thermal stability of corn oil flavoured with thyme flowers was determined and compared with that of the original refined corn oil (control). The oxidative stability index (OSI) was measured and samples were exposed to heating (30 min at 150, 180 and 200 degrees C) and deep-frying (180 degrees C). Changes in peroxide value (PV), free fatty acid (FFA) content, specific absorptivity values (K-232 and K-270), colour and chlorophyll, carotenoid and total phenol contents were monitored. RESULTS: The OSI and heating results showed that thyme incorporation was effective against thermal oxidation based on the increased induction time observed for the flavoured oil (6.48 vs 4.36 h), which was characterised by lower PV, FFA content, K-232 and K-270 than the control oil after heating from 25 to 200 degrees C, with higher red and yellow colour intensities and chlorophyll, carotenoid and total phenol contents. The deep-frying test showed the accelerated deterioration of both oils in the presence of French fries. CONCLUSION: Compared with the control oil, the thyme-flavoured oil showed improved thermal stability after heating. This could be attributed to the presence of thyme pigments and antioxidant compounds allowing extended oil thermal resistance. (C) 2011 Society of Chemical Industry