Tocopherol Content in Sweet Potato Tubers of Different Cultivar, Places Harvested and Cooking Methods

Abstract

Tocopherol (Toc) contents in nine cultivar of sweet potato tubers with known times and places of harvest were determined by the high performance liquid chromatography method, and changes in the content according to cooking methods. The following result was obtained.
1) Alpha-toc content was distributed in the order of the center>upper part>bottom part. But the distribution was not significantly different because of the wide deviations among individual values. There was also no difference in the toc content according to size.
2) The toc contents before and after cooking with different methods were compared. After roasting or microwave oven cooking, the toc content remained in quantities in the order of the bottom part>upper part>center. Steaming did not cause changes according to the parts of tuber.
3) Alpha-toc content difference according to cultivar was very small, which was attributed to different conditions at the places of harvest. This difference was especially noted in Simon.
4) As for changes in α-toc, that after heating was 41% of that of uncooked tubers. Compared to other species, Simon showed a high decomposition ratio for toc even after the microwave treatment which does not decompose the content so much. The remainder was much less after steaming or roasting.
5) Loss of water after cooking was considerably large in the order of microwave cooking<steaming<roasting. It was concluded that sweet potato tuber is one of the important sources of vitamin E similarly to edible oils because of a comparatively large amount ingested at one time despite its losses after cooking.