Physicochemical properties of glucomannan isolated from fresh tubers of Amorphophallus muelleri Blume by a multilevel extraction method

Abstract

Post-harvest treatment of Amorphophallus muelleri Blume (porang) tubers carried out by Indonesian farmers is slicing tubers into chips, drying, exporting, or processing them to a porang flour before export. To increase the economic value of porang tuber, it can be directly extracted to obtain glucomannan. Glucomannan is a polysaccharide that has many benefits. This work investigated the simple extraction method to produce high purity of glucomannan from fresh porang tubers and study the physicochemical properties of glucomannan. Sliced porang tuber repeatedly (three times) extracted by 60% ethanol (fixed concentration method). In addition, repeated extraction was conducted by varying ethanol concentrations (multilevel concentration method), in the first extraction, the sample was milled in 60% ethanol, then the precipitated sample was extracted again with 70% ethanol and finally extracted in 80% ethanol. Glucomannan with high purity (90.00%), whiteness degree (89.91), viscosity (14696.86 mPa.s), and a small number of impurities: ash (0.92%), fat (0.01%), protein (5.18%), without starch content was isolated by multilevel ethanol extraction method. By varying the concentration of ethanol, the impurities with different polarities could be dissolved effectively without heating, repetition of extraction, and further purification. FTIR spectra confirmed the presence of functional groups composing the glucomannan compound. XRD pattern showed that the extracted glucomannan had a more crystalline phase than commercial glucomannan. SEM results verified the purity of the appearance of glucomannan particles.