Fig. 3 reports the results of the FTIR analysis of the oil film that describes the spectral changes during the oxidation reaction of linseed oil. The initial spectrum is compared to the sample treated for 8 h at 80 °C. Several spectral changes could be observed including the disappearance of peaks at 3010 and 1654 cm−1, also the decrease of the peak at 722 cm−1. These peaks correspond to the cis åC–H stretch, cis CåC stretch and out-of-plane C–H bend [31] of the methylene group bridging the double bonds in the linoleic and linolenic acids. The appearance of a broad band centred at 3472 cm−1 is due to the presence of hydroxyl groups [31]. We also observe the formation of the 987 and 971 cm−1 peaks, that are attributed to trans-conjugated double bond and trans-out-of-plane C–H bend [16] and [27]. These observations indicate the transformation of non-conjugated cis configurations in molecules of unsaturated fatty acids to conjugated trans configuration, taking place concurrently with the formation of hydroxyl groups, as shown in Scheme 2.