1. Tropical Biosphere Research Center; University of the Ryukyus; Nishihara Okinawa 903-0213 Japan
2. Department of Bioscience and Biotechnology, Faculty of Agriculture; University of the Ryukyus; Nishihara Okinawa 903-0213 Japan
3. Product Development Division; Mitsui Sugar Co. Ltd; Tokyo 103-8423 Japan