1. National Food Research Institute, Tsukuba, Ibaraki 305-8642, Japan.
2. Graduate school of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan.
3. Corresponding author. Phone: +81-29-838-8029. Fax: +81-29-838-8122. E-mail: okadome@affrc.go.jp