Effect of seed coat extract from black soybeans on radial maze performance in rats.

1. In the present study, we tested the effect of seed coat extract from black soybeans on eight-arm radial maze performance in rats. 2. Rats were fed a diet containing 5% seed coat extract from black soybeans or a normal diet for 40 days. 3. One week after the start of feeding, rats were tested for learning ability related to two types of memory, reference memory and working memory, with a partially (four of eight) baited eight-arm radial maze. 4. A significant decrease in the total number of errors was observed 30 (mean value of five trials of 26-30 days) and 35 days (30-35 days) after the intake of the diet containing seed coat extract compared with the control group. In addition, the mean number of days taken to reach this criterion was significantly decreased after the intake of the diet containing the seed coat extract. 5. The number of reference memory errors was significantly decreased 30 and 35 days after the intake of the diet containing seed coat extract. However, no significant decrease was observed in the number of working memory errors. 6. From these results, it is concluded that the intake of seed coat extract from black soybeans effectively enhances memory and learning ability, especially long-term memory, in rats.