A high drying temperature causes degradation of sterols and tocopherols in yellow‐seeded Brassica napus oils

Abstract

The aim of the conducted investigations was to determine the effect of drying temperature on the changes in free fatty acid, phytosterol and tocopherol (T) contents in yellow‐seeded Brassica napus oils. Seeds were dried in a thin layer at 40, 60, 80, 100 and 120°C. Changes in phytosterols were assessed using GC‐MS, while tocopherols were assessed by HPLC. Degradation of phytosterols and tocopherols and an increased content of free fatty acids followed the applied drying temperature. During drying at 40 and 60°C, changes were statistically non‐significant, while at 120°C, losses of phytosterols reached 29% and tocopherols 23%. Practical applications: Drying of rapeseeds is an important stage of its production. However, we need to remember that these seeds are biological material highly sensitive to thermal treatment. Thus we need to search for the most advantageous conditions for their drying, with special emphasis on the preservation of bioactive components affecting human health. The analyses conducted compared the range of losses of bioactive components—phytosterols, tocopherols and plastochromanol‐8 during drying. Yellow‐seeded Brassica napus were dried in a thin layer at 40, 60, 80, 100 and 120°C. The effect of drying temperature on the free fatty acid, phytosterol and tocopherol content changes in oils was determined. Degradation of phytosterols, tocopherols and the increase in free fatty acid content were related to the applied drying temperature.

Antioxidant (Tocopherol and Canolol) Content in Rapeseed Oil Obtained from Roasted Yellow‐Seeded Brassica napus

“…Gawrysiak-Witulska et al . [15], by researching the effect of drying yellow-seeded rapeseeds, showed in a control sample (of oil from undried seeds) that the free fatty acid content was 1.13 mg KOH/g. Drying at 40 and 60 °C did not result in any statistically significant changes in the free fatty acid content.…”

“…Gawrysiak-Witulska et al . [15] studied the changes in tocochromanol in yellow rapeseed during the phases of postharvest processing, taking into account the drying of seeds under different temperature conditions (40, 60, 80, 100, and 120 °C). They showed that the initial tocopherol content of the seeds after collection was 610.5 mg/kg of oil.…”

“…These oils are not refined, they contain a large number of compounds coextracted with the lipids. Rapeseed oil is characterized by the ideal polyunsaturated fatty acid content with a 2:1 ratio of linoleic (n-6) versus linolenic (n-3) fatty acid and high contents of active biological compounds, such as tocopherols, plastochromanol-8, phytosterols and phenol compounds [12–15]. Rapeseed has the highest phenolic content among to other oilseeds (soybean, sunflower), about tenfold, however, phenols remain in the meal after pressing [16].…”

Degradation of tocopherols during rapeseed storage in simulated conditions of industrial silos

“…Similarly, research conducted by Goffman and Möllers (2000) demonstrated that PC-8 was degraded more readily than tocopherols during storage of whole rapeseed. PC-8 losses have also been noted during the process of yellow-seeded rapeseed drying (Gawrysiak-Witulska et al, 2015). However, detailed analysis showed that PC-8 losses induced by air-drying at a temperature of 40-60°C were greater than those of total tocopherols; in turn, at 100-120°C drying, the losses were smaller than those found for total tocopherols.…”

“…One-year storage of dried seeds at a temperature of 10ºC caused further losses. In investigations concerning drying the seed of the yellow-seeded variety, tocopherol losses were reported to reach 23% in the process of air-drying at 120ºC (Gawrysiak-Witulska et al, 2015). Furthermore, there have been investigations of tocopherol losses caused by improper conditions of rapeseed storage (moisture 10-15.5% and temperature 25-30ºC) (Gawrysiak-Witulska et al, 2011).…”