Synthesis and characterization of water-soluble O-carboxymethyl glucomannan derivatives

Water-soluble O-carboxymethyl glucomannan derivatives (O-CMG) with different degrees of substitution were synthesized successfully by reaction of a konjac glucomannan (isolated from the tubers of Amorphophallus paeoniifolius, one of the most abundant Amorphophallus species in Viet Nam forest) directly with monochloroacetic acid (MCA) without methanol. The structure of O-carboxymethyl glucomannan derivatives was characterized by FTIR, 1H, 13C and 1H–13C NMR-HSQC spectroscopy. The conditions for synthesizing of O-CMG derivatives were also evaluated. The results shown that the optimal conditions for carboxymethylation of glucomannan were pH 10, temperature of 60 °C for 3 h. The degree of substitution (DS¯) of O-substitution increased from 0.363 to 0.697 since the mass ratio (w/w) of glucomannan/monochloroacetic acid changed from 1/1 to 1/5.