Soybean seeds were collected from 5 sites in Japan (20 cultivars, 31 samples), and the quantities of isoflavone, thiamine (vitamin B1), riboflavin (vitamin B2) and tocopherol (vitamin E) were determined. Of the analyzed elements, isoflavone and a-tocopherol equivalent tended to change greatly among the sample seeds. Total isoflavone content ranged from 131.6 to 568.7 mg/100 g DW in the whole samples, and the mean value was 302.9 mg/100 g DW. The coefficient of variation was 40.7%. For each site, total isoflavone content tended to change more than other elements, so that isoflavone appears to be easily influenced by the growing conditions of cultivars. α-tocopherol equivalent ranged from 3.4 to 13.3 mg/100 g DW, with a mean value 5.6 mg/100 g DW, and coefficient of variation of 40.5%. In soybean seeds, changes in α- and β-tocopherol were large, and the nutritional value of soybeans as a source of vitamin E was greatly influenced by changes in a-tocopherol content. The coefficient of variation for thiamine and riboflavin were 13.0 and 10.3%, respectively, and their variation was smaller than isoflavone or α-tocopherol equivalent. Samples of soybean cultivar Fukuyutaka were collected from 11 sites in Kyushu, and the same analyses were conducted to investigate the influence of growing location. Results obtained were similar to those of the soybeans from all 5 sites. In conclusion, the selection of soybean type seems to be important when isoflavone or vitamin E is the purpose of soy food production.
