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

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 mu m (Chinese yam) to 34.5 mu m (Round leaf yellow yam). Corn starch BP has a mean granular diameter of 12.3 mu m. Chinese yam starch had the highest specific surface area (625.91 m(2)/kg) while Round leaf yellow yarn 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. (C) 2007 Elsevier B.V All rights reserved.