Differences between the stability of ��-, ��-, ��-, and ��-tocopherol as well ��-tocotrienol stored at -20 ��C and -80 ��C were studied in broccoli and blueberry samples. Before storage up to 28 days, they underwent different initializing processes such as freezing quickly with liquid nitrogen and freeze-drying, followed by homogenization. While ��-tocopherol levels in blueberries did not significantly differ, levels in broccoli were substantially higher after homogenization of freeze-dried samples compared to fresh broccoli samples. This might be caused by higher extractability of ��-tocopherol from the changed cell structure. Storage of fresh broccoli samples at -20 ��C led to decreasing ��-tocopherol levels. Nevertheless, the deviation between freeze-dried samples to the initial fresh samples and fresh samples frozen with liquid nitrogen stored at -20 ��C for 7 days were in the same order of magnitude. In conclusion, storage up to 7 days for vitamin relevant samples before analysis seemed to be justifiable.
