Effect of Adverse Storage Conditions on Oil Quality and Tocochromanol Content in Yellow-Seeded Breeding Lines of Brassica napus L.

Abstract

This study evaluated the contents of tocopherols and plastochromanol-8, as well as the acid values, in oils extracted from yellow-seeded Brassica napus L. lines stored under adverse post-harvest conditions. Seeds were stored at temperatures of 25°C and 30°C, with adjusted seed moisture contents of 10.5%, 12.5%, and 15.5%, corresponding to relative humidity levels of 81%, 85%, and 91%, respectively. A statistically significant reduction in total tocopherol content—up to 22% (p < 0.05)—was observed in seeds with the highest moisture content (15.5%) stored at 30°C. In contrast, seeds with 12.5% moisture stored at 25°C exhibited a smaller but still significant decrease of 11%–14% (p < 0.05). The lowest tocopherol degradation (2%–5%) occurred in seeds with 10.5% moisture stored at 25°C. Additionally, degradation rates differed between tocopherol homologues: α-tocopherol decreased more rapidly than γ-tocopherol, as evidenced by a significant decline in the α-T/γ-T ratio under high-moisture and high-temperature conditions. The most pronounced reduction in this ratio was recorded in seeds stored with 15.5% moisture at 30°C. Plastochromanol-8 was also highly sensitive to storage parameters, exhibiting an even more pronounced reduction than tocopherols under high-moisture conditions (p < 0.05). A significant increase in acid value was also observed under high temperature and moisture conditions, exceeding the acceptable threshold of 3.0 mg KOH/g in some cases, indicating advanced lipid hydrolysis during storage.