Effects of Storage Temperature and Duration on Bioactive Concentrations in the Seed and Oil of Brassica napus (Canola)

Abstract

The effects of storage temperature and duration on phytosterol, tocopherol and carotenoid concentrations are assessed in canola seed, and oil extracted using two different techniques, over a 10 month period. Increases to oxidation indices (K232, K270 and ΔK) are observed in the solvent extracted oils, and in the seed stored at 40 °C, indicating the formation of primary and secondary oxidation products. Only small decreases in the concentrations of γ‐tocopherol and β‐carotene are observed across the 10 month period. Phytosterol concentration decreases over time, with similar degradation rates observed in both seed and oils. α‐tocopherol and lutein are well preserved up to 7 months in all samples, despite oil oxidation, and further research will be needed to identify the cause for retention of bioactives. The results indicate that in order to preserve phytosterols, tocopherols and carotenoids in seed stored in bulk for extended periods, storage temperatures should remain at or below 21 °C. Moreover, oil stored at 4 °C or −18 °C, results in high bioactive concentrations and slows the onset of oil oxidation, compared to oil stored at room temperature. Practical Applications: Industrial storage conditions have been shown to greatly influence the chemical processes that occur with canola seed and oil. However, the effects of typical storage conditions on phytosterols, tocopherols and carotenoids in canola seed and extracted oil, are not yet known. This study presents the effects of typical seed and oil storage conditions on phytosterol, tocopherol and carotenoid concentrations, whilst monitoring oxidation indices and FFA, and thus provides information to seed handlers and oil processors on storage conditions that may preserve these bioactives. Moreover, the different behaviours of bioactives are examined relative to the oil extraction technique used, and present opportunities to optimise oil extraction techniques. Time series plots for α‐tocopherol concentrations in canola oil stored at different temperatures over 280 days, illustrating a difference in behaviour between the solvent extracted oil and the hand‐press extracted oil.

Changes in contents of phenolic compounds (sinapic acid derivatives) in seeds of Brassica napus L.under adverse storage conditions

“…In our earlier studies, we showed that adverse storage conditions (10-15% moisture content and temperature of 25-30°C) produce a statistically significant reduction in the level of lipophilic compounds such as tocochromanols and phytosterols (Gawrysiak-Witulska et al, 2012;. Flakelar et al (2018) also observed losses of phytosterols; however, they showed no statistically significant changes in the levels of individual phytosterols or their total contents in the function of temperature. They also showed that phytosterol losses were similar, irrespective of the fact whether their content was analysed in the samples stored as seeds or Fig.…”

“…In turn, seeds with a moisture content of 9-10% may be stored for 3 months (Salunkhe et al, 1992). Results reported by Flakelar et al (2018) indicate that the accumulation of free fatty acids will remain within the admissible limits for 10 months on condition the seed moisture content, oil exposure to light and exposure to extreme temperatures are limited to the minimum. According to Matthäus (2013), seeds with a 7% moisture content are stable during 9-month storage.…”

“…In the case of tocopherols, the authors showed that they were more stable than phytosterols in stored oil. The method of oil extraction was also crucial for tocopherol stability, with greater losses observed in the case of oil obtained by solvent extraction in comparison to pressing (Flakelar et al, 2018). Literature sources present scarce data on changes in the phenolic content of rapeseeds during storage.…”

Changes in contents of phenolic compounds (sinapic acid derivatives) in seeds of Brassica napus L.under adverse storage conditions [pdf]

“…In our earlier studies, we showed that adverse storage conditions (10-15% moisture content and temperature of 25-30°C) produce a statistically significant reduction in the level of lipophilic compounds such as tocochromanols and phytosterols (Gawrysiak-Witulska et al, 2012;. Flakelar et al (2018) also observed losses of phytosterols; however, they showed no statistically significant changes in the levels of individual phytosterols or their total contents in the function of temperature. They also showed that phytosterol losses were similar, irrespective of the fact whether their content was analysed in the samples stored as seeds or oil.…”

Quality evaluation of rapeseed oil in Chinese traditional stir‐frying

“…In fact, linoleic acids are usually used as indicators of the extent of fat deterioration because it is more susceptible to oxidation than saturated fatty acids. Therefore, the C18:2/C16:0 ratio is also used to indicate the degree of oxidative deterioration in frying oil (Flakelar et al ) . Overall, our results indicate that the oxidation resistance was higher in HCR than in LCR.…”