Canolol content

Because of its potent bioactive potential, the increase of canolol content in rape-seed oil would theoretically produce oil with enhanced food value and as well as longer shelf life (Spielmeyer et al, 2009). Canolol is thermally unstable, even though it is being produced from sinapic acid at higher temperatures. An exponential decrease in the canolol content from 81.4 to 11.0 g/g in oil was observed when it is exposed to a heat treatment up to a temperature of 180°C for 20 min. 

Canola oil is conventional cooking oil in many countries. The canolol content of crude canola oil (220-1200 ppm) could provide doses similar to that used in a study by Cao et al. (2008). It should be noted, however, that the concentration in refined canola oil is significantly lower (Wakamatsu et al., 2005) so that alternative strategies have to be proposed. Supplementation of canola oil with extracted or synthesized canolol will be an effective method to enrich and add value to the oils. 

Spielmeyer A, Wagner A, Jahreis G. 2009. Influence of thermal treatment of rapeseed on the canolol content. Food Chemistry, 112 944—948. 

FIGURE 17.7 Canolol content of virgin canola oils from the German market... 

In the literature, canolol is described as an effective antioxidant (Koski et al., 2003 Kuwahara et al., 2004 Vuorela et al., 2005 Wakamatsu et al., 2005). Figure 17.8 shows increased oxidative stability of canola oil accompanied increasing amounts of canolol. Using the Rancimat test at 120°C canolol contents below 200 itg/g in canola oil from roasted seeds resulted in slight decrease of the oxidative stability. In contrast, amounts of canolol higher than 200 g/g improved oxidative stability of the oil dramatically. Wijesundera et al. (2008) also showed an improvement in... 

FIG U RE 17.4 Influence of temperature during roasting on formation of canolol and content of tocopherols. 

At higher contents of canolol in the oil, a good correlation with the oxidation stability using the Rancimat test was found. If the temperature load was <15 min at 180°C, a decrease in the oxidation stability was observed due to the low formation of canolol. With increasing temperature load, the oxidation stability increased from 4 to 7 h, before the oxidation stability decreased again as a result of a temperature load of more than 45 min at 180°C. At a low temperature load, less canolol is formed so that the temperature is sufficient to impair the oxidation stability of the oil. Only when the content of canolol in the oil from roasted seeds increases does oxidative stability improve. If the temperature load is too high, the impairment of the oil is faster, then the formation of canolol can improve the oxidation stability. 

The effect of canolol on the storage stability was confirmed by storing canola oil at 60°C over 168 h. The parameters used to monitor the oxidative state of the oil were diene absorption as well as the hexanal content. An increase of absorption at 240 nm was found as a resnlt of a shift of the double bond in unsaturated fatty acids during oxidation. Hexanal, a key compound of the oxidation of fats and oil can be used as an indicator to follow the extent of oxidation. 

Canola seeds were roasted at 180°C for different times ranging from 5 to 60 min and the oil extracted and stored at 60°C for 168 h. While the content of tocopherols was similar for all oils, remarkable differences in the content of canolol were found. 

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