FACTORS AFFECTING THE VISCOSITY OF FREEZE -DRIED YAM

Factors which affect the viscosity and viscous polysaccharide of freez e-dried yams were investigated. (1) Three kinds of yam (Jinenjo (Diosc orea japonica), Thukune-imo (D. opposita) and Sore-yam (D. alata L.)) were freeze dried. The viscosity of freeze-dried Sore-yam was the high est. The decrease of the content of viscous polysaccharide in freeze-d ried yams was most remarkable in Jinenjo. The sucrose content in Jinen jo was less than that in Sore-yam, suggesting that the sucrose content in yams affects the viscosity of freeze-dried yam bacause sucrose add ition stabilized the viscosity of freeze-dried Jinenjo. (2) The change of viscosity was minimal during freeze drying, while there was a sign ificant decrease in the content of viscous polysaccharide during stora ge. As storage temperature was increased, the viscosity of freeze-drie d yam decreased during storage. Freeze-dried yam wrapped in nylon-poly ethylene laminate absorbed water during storage. Water absorption of d ried yam accelerated the viscosity change. (3) The viscosity of freeze -dried yam acidified before freeze drying decreased as the pH of the y am was lowered. (4) Viscous polysaccharide was purified with SDS-ethan ol and freeze dried. During storage at rom temperature, freeze-dried v iscous polysaccharide changed from water-soluble to water-insoluble. I t was ascertained that polysaccharide insolubility was one of the sour ces of the viscosity change of freeze-dried yam.