1. Department of Food and Nutrition Sciences, Graduate School of Dairy Science Research, Rakuno Gakuen University, 582 Bunkyodai Midorimachi, Ebetsu, Hokkaido 069-8501, Japan, and Graduate School of Agriculture, Hokkaido University, Kita 9, Nishi 9, Kita-Ku, Sapporo 060-8589, Japan