1. Department of Microbiology, Yamaguchi University School of Medicine, Ube 755-8505, Japan
2. Department of Food and Nutrition, Yamaguchi Prefectural University, Sakurabatake, Yamaguchi 753-8502, Japan
3. Institute of Genetic Ecology, Tohoku University, Katahira, Sendai 980-8577, Japan
4. Department of Food Macromolecular Science, Institute of Food Research, Earley Gate, Whiteknights Road, Reading RG6 6BZ, UK