Antioxidant activity and phytochemical content of cold‐pressed rapeseed oil obtained from roasted seeds

Abstract

An analytic comparison was made of cold-pressed rapeseed oil produced from unroasted seeds and coldpressed oil produced from seeds that had previously undergone roasting at temperatures of 140 °C, 160 °C, and 180 °C for 5, 10, and 15 min. It was determined whether the duration and temperature of roasting have any qualitative and quantitative effects on the contents of the native antioxidants (tocopherol, PC-8, phenolic compounds, canolol, and phytosterols) found in rapeseed oil. At the same time, changes in the antioxidant activity of oils produced from roasted seeds were determined. It was shown that roasting has no significant effect on the quality of cold-pressed oils. The peroxide value of the oils ranged from 2.03 to 3.48 meq O 2 /kg, while the acid value did not exceed 0.68 mg KOH/g. Slight changes were observed in oils in terms of tocochromanol contents. A decrease was seen mostly in the level of the -T homologue, with an increase in the contents of -T and PC-8 (in oil from seeds roasted at 180 °C). In the oil from the unroasted seeds, the canolol content was 11.54 g/g oil. It was shown that increases both in temperature and in duration of seed roasting result in a statistically significant increase in the canolol content of cold-pressed oils. For the seed roasted at 180 °C for 15 min, this increase was fiftyfold (609.94 g canolol/g oil). The same roasting conditions also led to a twofold increase in the antioxidant activity of the oil. Practical applicationsCold-pressed oils are increasingly frequently chosen by consumers due to their reputation as good source of bioactive components. An obvious example of such a food product is cold-pressed rapeseed oil made from roasted seeds, in which the levels of canolol-a product of the decarboxylation of sinapic acid-is markedly increased. This compound is ascribed strong antioxidant properties, as well as antimutagenic and anticarcinogenic properties. Such oils truly deserve to be labeled bioactive products. www.ejlst.com European Journal of Lipid Science and Technology ccep t e d A Artic le Graphical abstractAn analytic comparison was made of cold-pressed rapeseed oil produced from unroasted seeds and coldpressed oil produced from seeds that had previously undergone roasting at temperatures of 140 °C, 160 °C, and 180 °C for 5, 10, and 15 min. It was determined whether the duration and temperature of roasting have any qualitative and quantitative effects on the contents of the native antioxidants (tocopherol, PC-8, phenolic compounds, canolol, and phytosterols) found in rapeseed oil. In the oil from the unroasted seeds, the canolol content was 11.54 g/g oil. It was shown that increases both in temperature and in duration of seed roasting result in a statistically significant increase in the canolol content of cold-pressed oils. For the seed roasted at 180 °C for 15 min, this increase was fiftyfold (609.94 g canolol/g oil). The same roasting conditions also led to a twofold increase in the antioxidant activity of the oil.

Cold-pressed and hot-pressed rapeseed oil: The effects of roasting and seed moisture on the antioxi- dant activity, canolol, and tocopherol level

“…The rapeseeds were roasted for 15 minutes at 160°C, according to the method presented in earlier work (Siger et al, 2015).…”

“…Kraljić et al (2013) reported that conditioning has a statistically significant effect, increasing the α-T contents of the oil; however, they found no significant effects of conditioning on the level of γ-T. In studies examining the levels of tocopherols in rapeseed oil produced from roasted seeds, some authors observed an increase in the amounts of particular tocopherols and plastochromanol-8 (Siger et al, 2015;Shrestha and De Meulenaer, 2014). Neither Wakamatsu et al (2005) nor Spielmeyer et al (2009) found any significant differences in the tocopherol content of canola oil from unroasted and roasted raw material.…”

“…Neither Wakamatsu et al (2005) nor Spielmeyer et al (2009) found any significant differences in the tocopherol content of canola oil from unroasted and roasted raw material. The lack of a decrease in tocopherol levels under the influence of high-temperature roasting of the rapeseed is often explained by the synergistic interaction of phenolic compounds (here, mainly canolol) -the amount of which increases in proportion to the temperature and roasting duration (Matthäus, 2013a;Siger et al, 2015). Other compounds may also reduce the losses of tocopherols during roasting.…”

“…Shrestha and De Meulenaer (2014) roasted rapeseeds for 10 to 90 minutes at a temperature of 180°C and demonstrated that the highest amount of canolol can be found in extracted oil produced from seeds roasted for 20 minutes. Siger et al (2015) analyzed the amount of canolol in cold-pressed rapeseed oil produced from seeds roasted at 140°C, 160°C, and 180°C for 5, 10, and 15 minutes. The highest canolol levels were found in the oil produced from seeds roasted at 180°C for 15 minutes (these contained 50 times more canolol than in the control test).…”

“…The amount of canolol in the oil produced from the seeds roasted at 160°C for 15 minutes was 244.76 µg/g for the PR46W20 cultivar. In the control test (using oil produced from unroasted seeds), the levels of canolol were 5.8 µg/g (Spielmeyer et al, 2009), 5.19 µg/g (Shrestha andDe Meulenaer, 2014), and 11.54 µg/g (Siger et al, 2015). Kraljić et al (2013) showed that conditioning the seeds prior to pressing the oil had a significant effect on canolol level.…”