Vitamin D_2 in Shiitake (Lentinus edodes) was identified and determined. The results obtained were as follows : (1) Vitamin D_2 in Shiitake was identified by HPLC, UV spectrum and GCMS, whereas 25-OH-D_2 could not be detected in it. (2) The HPLC-method reported previously (J. Nutr. Sci. Vitaminol., 30, 11-25, 1984) was confirmed to be also useful for the determination of vitamin D_2 in Shiitake. The recovery and coefficient value were 102.5±4.8 (M±SD)% and 4.6%, respectively, which were satisfactory. (3) The assayed values of vitamin D_2 In raw Shiitake (No.1 and 2) cultured outdoors (averages: 310 and 390_<IU>/100g) were higher than those cultured in a vinylhouse (73_<IU>/100g). In the case of dried Shiitake, vitamin D_2 values obtained Koshin cultured and picked up in September (the shape of pileus is spread, 969_<IU>/100g) were higher than those in Donko cultured and picked up in February (the shape of pileus is closed, 300_<IU>/100g). The results suggested that vitamin D_2 in Shiitake was photochemically produced from ergosterol during cultivation by solar radiation. (4) The assayed values of ergosterol in the samples of shiitake mentioned above were much higher than those of vitamin D_2 (about 6,500〜46,000 times as weight ratio). (5) Vitamin D_2 was not solubilized into water by Soaking or boiling of dried Shiitake with water. However, the content of vitamin D_2 decreased gradually during boiling, which suggested that the vitamin was not solubilized into water but destroyed during boiling. On the other hand, the vitamin was not destroyed by oil cooking (Fried with an oil for 2 min or in an oil for 1 min).
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