Surface properties of yam ( Dioscorea sp.) starch powders and potential for use as binders and disintegrants in drug formulations

Abstract

A comparative investigation of the surface properties of starch powders from three species of yam ( Dioscorea spp.) was conducted, using corn starch BP as reference standard, with a view to assessing their usefulness as ingredients of tablets/capsule formulations. Significant differences were observed in the physicomechanical properties of the starches obtained from the various yam species. Granular diameter ranged from 5.4 μm (Chinese yam) to 34.5 μm (Round leaf yellow yam). Corn starch BP has a mean granular diameter of 12.3 μm. Chinese yam starch had the highest specific surface area (625.91 m 2/kg) while Round leaf yellow yam had the lowest (117. 4 m 2/kg); corn starch BP has a specific surface area of 232 m 2/kg. The surface tension of the starch mucilage also varied significantly with Bitter yam having the lowest (44.56 mN/m) and Round leaf yellow yam the highest (54.00 mN/m); corn starch had a surface tension of 62 mN/m. X-ray powder diffraction revealed three distinct crystalline patterns: Bitter yam and corn starch displayed the type A while Round leaf yellow yam and Chinese yam displayed the types B and C patterns respectively. In moisture adsorption, all the starches studied displayed monolayer adsorption profiles with rate order of moisture adsorption ranging from 0.92 mg%/h for Chinese yam to 1.07 mg%/h for Round leaf yellow yam starch. Since co-formulated materials will react or interact at the interface, the variations observed in the surface properties suggest a potential for significant botanical specie-dependent differences in performance of starch powder in formulated dosage forms.