Changes in tocopherol and plastochromanol-8 contents in seeds and oil of oilseed rape (Brassica napus L.) during storage as influenced by temperatureand air oxygen

The changes in tocopherol and plastochromanol-8 contents in seeds and oil o f oilseed rape (Brassica napus L.) were studied during a storage period of 24 weeks at different incubation temperatures and exposure to air oxygen (o pen and closed flasks). In the extracted oil, total tocopherol content rema ined unaltered at 5 and 20 degrees C throughout the 24 weeks of storage. At 40 degrees C, a beginning degradation was observed already after 4 weeks i n both open and closed flasks; the cl-tocopherol content was affected most, followed by gamma-tocopherol and plastochromanol-8. After 16 weeks at 40 d egrees C, the total tocopherol content in the oil was reduced by more than 90%. In intact seeds, no tocopherol degradation was observed; only the seed s incubated at 40 degrees C and in open flasks showed slightly lower tocoph erol contents. However, the analysis of the tocopherol composition in the s tored seeds showed a decrease in the alpha-tocopherol content and an increa se in the gamma-tocopherol content, which resulted in a decreasing alpha-/g amma-tocopherol ratio. This trend was most apparent at 40 degrees C and aft er 24 weeks of storage. A reduction of plastochromanol-8 occurred only at 4 0 degrees C and was more pronounced in open flasks. At 40 degrees C and in closed flasks a gradual increase in the content of alpha-tocotrienol was ob served, a compound normally not accumulated in rapeseed.