Quality of Konjac Flour and Its Objective Measures

Abstract

The sol-marking property and the konnyaku-forming ability of konjac flour (gluco-mannan) were investigated on 9 samples from 3 varieties, native, shina and haruna-kuro, in connection with their grades. The viscosity of the 1% sol, ηc=1% measured by a Brookfield-type viscometer closely related to the grade of the flour except 2 samples from shina, which seemed to be a peculiar variety producing a fragile gel in spite of its ability to make a highly viscous sol. The breaking strength, S (g) and the breaking deformation, d (cm) of the konnyaku-gel, both of which were obtained by the penetrating-test using Okada's jelly-strength tester, were also examined as measures of the flour grade. S was related to the concentration C by the following equation; S=kCⁿ, where the parameter k was almost the constant value ca. 100g without regard to the kinds or grades of the flour, whereas n varied 1.3 to 1.8 with the flour grade. On the other hand, d was little influenced by the concentration and the values seemed to be intrinsic for each kind of the flour. ηc=1% and n and d for the 3% gel were recommended as the objective measures for evaluating the qualities of konjac flour.