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.