Cooperative Study with China
Professor Chong-Ren Yang, Kunming Institute of Botany (Yunnan) got PhD in Hiroshima on 1996 under the supervision of Former Professor Osamu Tanaka. Since then, we have been collaborating with his institute and several scientists from the same institute followed him to study in our lab. From 1991 to 1993, followed by the first visit (1987-1988), the second international cooperative research funded by Monbusho helped the visit of Ohtani, Kasai and Yamasaki to Kunming for field work as well as negotiation for collaboration with Chinese group.
On 1997 Prof. Yang organized International Symposium of glycosides at Kunming, and Yamasaki was invited to present a Plenary lecture on Non Cyanogenic Cyano-Glycoside, and visited local tribe village (for tourists), and Northern Yunnan as a post symposium tour.
Prof. Tanaka (Emeritus) collaborated with many other institutes in China mainly on Panax spp (Araliaceae). Hemslea spp (Cucurbitaceae) was also one of the main target plants. Prof. Tanaka and Dr. Kasai isolated many saponins from these plants as a cooperation research with China.
Research on natural sweeteners started from Prof. Tanaka and his group found a sweet diterpene glucoside, rubusoside from Rubus suavissimus (Rosaceae). Unexpectedly, it is a congener of famous stevioside isolated from Stevia rebaudiana (Compositae). Although the magnitude and the quality of rubusoside is inferior to stevioside, we tried to improve it's sweetness by adding several glucose units via enzymatic transglucosylation successfully. This method was applyed on the improvement of stevioside as well.
Apart from these works, Dr. Kasai and his group found variety of new sweet substances from Labiatae (diterpenoids), Cucurbitaceae (triterpenoids) and Juglandaceae (flavonoids). Research on the structure-sweetness relationship of these substances is in progress.