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The long‐term storage of cold‐pressed oil from roasted rapeseed: Effects on antioxidant activity and levels of canolol and tocopherols
Author(s) -
Siger Aleksander,
Michalak Michał
Publication year - 2016
Publication title -
european journal of lipid science and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.614
H-Index - 94
eISSN - 1438-9312
pISSN - 1438-7697
DOI - 10.1002/ejlt.201500183
Subject(s) - rapeseed , food science , chemistry , roasting , dpph , tocopherol , antioxidant , peroxide value , biochemistry , vitamin e
The aim of this study was to determine the oxidative stability of rapeseed oils cold pressed from seeds roasted at 140, 160, or 180°C for 5, 10, or 15 min versus the control (oil from unroasted seeds). The oils were stored for a period of 1 year. After 6 and 12 months of storage, the samples were analyzed to determine their peroxide and acid values, the levels of bioactive substances (tocopherols, plastochromanol‐8, and canolol), as well as antioxidant activity (DPPH test). It was shown that roasting the rapeseeds had a significant effect on the oxidative stability of the oils, which increased by almost 50%. In the case of oils pressed from seeds roasted at 140 and 160°C, it was shown that the longer the seeds were roasted, the smaller the reduction in canolol content. After 6 months of storage, the percentage decrease in the canolol content of oils from roasted seeds was recorded to be at a level comparable to that of the control. After 1 year of storage, the percentage loss of canolol was markedly lower (from 18 to 45%) than in the control (61%). The reduction in tocopherol levels was dependent on the duration of storage and on the type of sample. Principal component analysis (PCA) confirmed that the oxidative stability of oils produced from roasted seeds, particularly from those roasted at 180°C, was markedly higher than that of the other samples obtained from roasted seeds and the control. Practical applications: Studies concerning oxidative stability are most typically conducted by applying so‐called accelerated aging tests performed at high temperatures (Rancimat, Oxidograph test). In practice, this undermines the reliability of the results, since it is difficult to draw conclusions about the actual shelf life of a product, on account of the various mechanisms of the oxidation process. At high temperatures, the primary reactions are connected with polymerization and cyclization, which are not comparable to the reactions taking place under normal conditions. The analysis conducted here made it possible to follow the changes during the storage of the oil and the rate of degradation of bioactive substances reflecting cold‐storage conditions. Rapeseed oils cold pressed from seeds subjected to roasting (140–180°C for 5–15 min) were compared to rapeseed oil that was cold pressed from seeds not exposed to elevated temperatures through an analysis of their oxidative stability, antioxidant activity, and levels of bioactive substances (tocopherols, plastochromanol‐8, and canolol). The oils were stored for a period of 12 months at a temperature reflecting cold storage conditions (4°C). It was shown that the oils produced from seeds roasted at 180°C in particular exhibited greater oxidative stability and the best antioxidant properties. Antioxidant activity was shown to correlate with the levels of canolol ( r = 0.9927; p < 0.0001) and g‐T ( r = 0.9765; p < 0.0001), as well as with total tocopherols ( r = 0.9796; p < 0.0001).