High purity glucomannan after ultrasonic-assisted extraction and α-amylase liquefaction of porang flour

Glucomannan extracted from the porang plant (Amorphophallus oncophyllus) is encapsulated by starch impurities. The main objectives of this study were to evaluate the effect of purifying glucomannan using thermostable α-amylase, ultrasonic-assisted extraction (UAE), and the combination of both treatments on glucomannan purity and the physiochemical properties of the porang flour, such as viscosity. This research was conducted through four main steps as follows: thermostable α-amylase production and preparation, liquefaction, extraction, and purification of glucomannan with ethanol, and the glucomannan properties assay. The liquefaction process was carried out at 70°C, at which α-amylase exhibited maximum activity. The combined treatment of UAE and α- amylase liquefaction successfully purified glucomannan from porang flour. This treatment significantly reduced starch and ash contents, increased glucomannan content to 89.69%, lowered viscosity to 160 cP, and enhanced solubility to 46.18%. This treatment improved the transparency and lightness of the flour. The pure glucomannan granules obtained by combining UAE and the enzyme treatment showed regular shaped and relatively smooth with more hydroxyl and carbonyl groups than the other treatments. These results provide an alternative method to obtain pure glucomannan by combining UAE and thermostable α -amylase liquefaction.