Characteristics of the Three Species of Yam (Dioscorea) for Karukan Making

Abstract

Kagoshima-shi 891-O1 Karukan, a traditional sponge cake in the Southern Kyushu, is originally made from rice powder and homogenized yam, and it is well- known that Jinenjo (the native Japanese yam, Dioscorea japonica THUNB) is most preferable to make Karukan. Here, for making Karukan, the characteristics of Jinenjo were elucidated, and the availability of the Tsukuneimo (cultivated in Japan, Dioscorea opposita THUNB) and KaU-09 (cultivated in SouthernEast Asia, Dioscorea alata L.) was investigated comparing with Jinenjo. At first, on 26 kinds of Karukan on the market in Kagoshima, correlation between their sensory score and texture characteristics were estimated. Elastic deformation measured under a constant load (100g) by a creep meter and also distance to rupture point (L-value) measured by a tensile machine correlated well with sensory score. Sensory score of Karukan increased with increasing elastic deformation and L-value. It was found that undesirable quality change of Karukan after storage was caused by retrogradation of starch, which was retarded by increasing water content in Karukan. The amount of water to be added to Karukan dough was depended on the viscosity of yam. Water holding capacity of dough made from high viscous yam was large. Accordingly, most viscous Jinenjo was preferable to make highly evaluated Karukan. Although KaU-09 showed high viscosity next to Jinenjo, Karukan made from it was very poor in textural quality showing less elastic deformation and large adhesiveness. This fact was ascertained to be caused by amylolytic action of amylase occurring in KaU-09. As KaU-09 amylase was poor in heat resistance, the pretreatment of homogenized yam at 60°C for 1h could improve the characteristics of KaU-09 for Karukan making by inactivating amylase.