Characterization of glucomannan from some Amorphophallus species in Vietnam

In this work, konjac glucomannans (KGM) have been isolated from Amorphophallus tubers (used three Amorphophallus species: Amorphophallus panomensis, Amorphophallus paeoniifolius and Amorphophallus tonkinensis) by a simple method without using toxic chemicals. The konjac glucomannan content was about 5–9% (w/w) of original Amorphophallus tubers. The structure, moisture uptake, molecular weight of konjac glucomannan were investigated by nuclear magnetic resonance spectroscopy (NMR), differential scanning calorimetry (DSC) and viscosimetry. The results indicated that the main component of konjac flour was glucomannan. The mannose/glucose molar ratio and molecular weight (Mw) of glucomannan isolated from Amorphophallus paeoniifolius, Amorphophallus panomensis and Amorphophallus tonkinensis were 1/0.13; (Mw = 1.115 × 106), 1/0.10; (Mw = 1.023 × 106) and 1/0.25; (Mw = 1.043 × 106), respectively. The moisture uptake of konjac glucomannans was about 7.5–9.2%.