Development and validation of visible spectrophotometric method for the determination of total D-glucose and D-mannose levels calculated as glucomannan in porang powder (Amorphophallus oncophyllus) and Konjac powder (Amorphophallus konjac)

Abstract

Objective: Porang or konjac is one type of tubers that are widely used in industry, food, cosmetics, and
medical. Porang and Konjac contain glucomannan, a polysaccharide consisting of D-glucose and D-manosa.
Materials and Methods: One way to determine the content is using phenol-concentrated sulfuric acid reagent
with visible spectrophotometric method. Before determinate how much glucomannan in porang, the color
stability test and method validation were performed. Results: From the color stability test, the absorbance was
observed after 180 min. For the validation result, the selected wavelength was 492.0 nm, and the equation of
regression was y = 0.0266x+0.0019 (r = 0.9992 > r table = 0.834) and Vxo 2.16%, while the precision gave the
coefficient of variation 0.54% and accuracy gave average recovery for porang powder (99.60 ± 0.86% w/w)
and konjac powder (100.48 ± 0.56% w/w). Conclusion: The determination of glucomannan was carried out in
two samples, which were taken from Indonesia (porang powder) and China (konjac powder). The result showed
that the concentration of glucomannan in porang powder was 52.33 ± 0.74% (w/w) and in konjac powder was
61.24 ± 0.60% (w/w).