Physicochemical properties of acetylated glucomannan of Amorphophallus onchophillus as excipient of drug controlled release

Amorphophallus onchophillus is a local tuber rich in glucomannan, a hydrocolloid polysaccharide composed of β-1, 4 linked D-glucose and D-mannose. Glucomannan has valuable properties such as water soluble, forms film readily, biodegradable and biocompatible. However, hydrogen bonding could be introduced during glucomannan purification and drying process. This hydrogen bonding is responsible for formation of insoluble glucomannan. Acetylation of glucomannan effectively decreases the hydrogen bonding and increases its solubility which helps in the drug release system. Application of glucomannan as drug controlled release (DCR) excipient had been reported. For this application, it requires glucomannan at the range of degree of substitution (DS) 0.8-0.9. Previous research of acetylated glucomannan required a minimum of 2h reaction to achieve DS 0.8-0.9. Meanwhile, acetylated cellulose using phosphoric acid as catalyst reached 2.8 of DS only in 30 min. The objective of this work was to study the physicochemical properties of acetylated glucomannan for DCR excipient by using phosphoric acid as catalyst. The results showed the higher acetic acid concentration, the longer reaction time and the higher temperature showed a positive impact on DS due to the more acetyl group of the acid replaced the hydrogen bond of glucomannan. This higher DS had a positive impact on the solubility, viscosity, and swelling power of modified glucomannan. Higher glucomannan concentration, however, reduced the DS and showed a negative effect on the physicochemical properties of the modified glucomannan. For DCR excipient, the acetylation was recommended to be conducted using 8.0 M of acetic acid and 1% of glucomannan at 30°C for 60 min which resulted in a DS of 0.899. The morphology determination revealed the surface of acetylated form was smoother than that of the native glucomannan. The acetylated form showed an increase of absorbance at about 1740 cm−1 assigned to acetyl groups.