TEMPO-oxidized Konjac glucomannan as appliance for the preparation of hard capsules

• OKGM polymers offer a new option for preparing vegetarian hard capsules.
• OKGM hard capsules were satisfactorily qualified for gastric soluble capsules.
• OKGM of higher DO is superior to prepare hard capsule than OKGM of lower DO.

TEMPO-oxidized Konjac glucomannan (OKGM) was developed as new material for preparing vegetarian hard capsules. OKGM of different degrees of oxidation: DO30%, DO50%, and DO80% were prepared to select optimum DO for capsule formation. FT-IR results proved that the primary alcohol groups on KGM were oxidized into carboxyl groups. XRD analysis suggested that TEMPO-oxidation decreased the crystallinity of KGM. DO80% was considered as the optimum candidate for capsule preparation owing to its superior solubility, transparency and reduced viscosity. The hydrophilicity of OKGM films, measured by contact angle measurement, increased with increasing DO. The elongation at break and tensile strength of the OKGM films enhanced with increasing DO. In vitro drug dissolution profile of OKGM capsules showed that the shell rupture time of DO80% capsule is about 5–10 min, and 80% of the drugs were released within 30–45 min. Thus DO80% OKGM was qualified to be used for gastric soluble hard capsules.