Canolol, tocopherols, plastochromanol‐8, and phytosterols content in residual oil extracted from rapeseed expeller cake obtained from roasted seed

Due to the high canolol content rapeseed oil is increasingly often pressed from seeds subjected to the roasting process. However, there is a lack of data on the contents of canolol in residual oil produced from cake, a by‐product of cold pressing. The aim of this study was to investigate the contents of bioactive substances contained in expeller cake generated in cold pressing of rapeseed oil from seeds roasted at a temperature of 140, 160, and 180°C for 5, 10, and 15 min. Contents of tocopherols, plastochromanol‐8, and canolol were analyzed using the NP‐HPLC‐FL method, while contents of phytosterols – by GC‐FID. Based on the recorded data it may be concluded that 180°C is the best temperature for seed roasting, since at that temperature the greatest amount of canolol is formed and most of it passes to oil in the course of cold pressing. Contents of tocopherols in the tested oils ranged from 88.48 to 90.51 mg/100 g. A lower tocopherol content was recorded in residual oil of the press cakes in comparison to cold‐pressed oil, particularly in the case of samples roasted at a temperature of 160 and 180°C. Content of PC‐8 was higher in residual oil by over 4 mg/100 g in comparison to cold‐pressed oil. Also the total content of phytosterols in oils produced by solvent extraction from cake was higher than in cold‐pressed oil. Contents of phytosterols ranged from 4141.9 to 4826.1 μg/g oil. Practical application: Rapeseeds increasingly often are subjected to roasting prior to the cold pressing process. During roasting canolol is formed, which as a product of decarboxylation of sinapic acid, more efficiently penetrates to oil in comparison to sinapic acid. However, there is no data concerning the amounts of canolol remained in press cake. This study investigated the effect of temperature of rapeseed roasting on the content of bioactive compounds (tocopherols, PC‐8, phytosterols, and canolol) in residual oil from press cake. Results recorded in this study facilitate selection of roasting parameters so that the lowest possible amounts of bioactive compounds are retained in cake and they rather pass to cold‐pressed oil, enriching it and indirectly contributing to an enhancement of its oxidative stability. On the other hand, these results show that the expeller cake (from roasted seeds) as a by‐product can be further treated as a good source of bioactive compounds including canolol. They can also be used as a practical supplement to animal feed. This study investigates the effect of rapeseed roasting at a temperature of 140, 160, and 180°C for 5, 10, and 15 min on the content of residual oil and its composition in terms of such bioactive substances as tocopherols, PC‐8, phytosterols, and canolol. It is seen that residual oil extracted from rapeseed cake subjected to roasting has lower contents of tocopherols (particularly in the case of samples roasted at 160 and 180°C). PC‐8 is more effectively extracted with an organic solvent, since its content in residual oil was by 4 mg/100 g higher than in cold‐pressed oil. Also the content of phytosterols is higher in residual oil than in cold‐pressed oil. Contents of phytosterols ranges from 4141.9 to 4826.1 mg/g oil. Based on the recorded data it may be concluded that 180°C is the best temperature for seed roasting, since at that temperature the greatest amount of canolol is formed and most of it passes to oil in the course of cold pressing.