Preparation and characterization of modified dioscorea bulbifera starch and evaluation of its use as a disintegrant in tablet formulations

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Addis Ababa Universty


Starch is a naturally occurring biodegradable polysaccharide. It is found in different parts of plant organs, including seeds, fruits, tubers, roots and bulbil. Locally, Dioscorea bulbifera is a rich source of starch that forms an important dietary supplement. Starch is usually modified either chemically or physically to overcome shortcomings of native starch, making them more suitable for specific uses. This study aims to prepare modified D. bulbifera starch (DBS) by pregelatinization and carboxymethylation and evaluate its disintegrant effect in tablet formulations. In this study, DBS was isolated from bulbil and modified by pregelatinization and carboxymethylation. Pregelatinized starch was prepared using 2:1(water to starch ratio) that was heated at 64 ˚C for 15 min. Carboxymethylation was carried out in 80% isopropanol at different molar ratio of monochloroacetic acid: anhydrous glucose unit (MCA:AGU) (0.2:1, 0.6:1 and 1:1) and at 20% and 30% of NaOH using native and pregelatinized D. bulbifera starch (PGDBS). The influences of the amount MCA, NaOH and types of starch on degree of substitution (DS) of carboxymethylated starch were investigated. Properties of pregelatinized and carboxymethylated starch such as, densities, flow, swelling power, percentage solubility and moisture sorption were investigated and compared to those of native D. bulbifera starch (NDBS), Starch 1500® and sodium starch glycolate (SSG). Tablets were produced by wet granulation method using modified DBS as disintegrant at different concentrations: PGDBS (5%, 7.5%, 10% and 12.5%), sodium carboxymethyl DBS (SCMDBS) and sodium carboxymethyl pregelatinized DBS (SCMPGDBS) (2%, 4%, 6% and 8%) using paracetamol as a model drug. The granules prepared at constant binder concentrations (povidone 3%) were characterized for density related properties and flow properties and the tablets were tested for weight uniformity, crushing strength, friability, disintegration time (DT) and dissolution rate using standard methods. FTIR spectral findings show the presence of the carboxymethylated group on modified starch granule with new band at 1593.09 cm-1; and for pregelatinized starch weak absorption at 1610 cm−1 due to bound water. The FTIR of a mixture of paracetamol and SCMDBS or PGDBS showed no interaction. Both were found to be compatible with paracetamol. The DS value increased with increasing molar ratio of MCA: AGU from 0.2 to 1 with 30% NaOH. Higher DS obtained with SCMDBS (0.36652+0.021) showed higher swelling power followed by SSG and SCPGDBS. The moisture sorption profiles indicated that the relative humidity during tablet production and storage should be carefully monitored. The shortest DT was obtained for tablets prepared at 4% disintegrant concentration with SCMDBS (0.49+0.01 min) followed by SSG (0.5+0.01 min) and SCMPGDBS (0.53+0.011 min). Swelling power exhibited some direct effect on disintegrant VIII activity of the starches. The tablets prepared with PGDBS and Starch 1500® exhibit comparable characteristics. The results also indicated that the properties of paracetamol tablets formulated with native and modified starches as disintegrants were affected by their concentration and nature of disintegrant. The dissolution studies of paracetamol tablets fulfilled USP requirements (quantity dissolved in 30 min ≥ 80%). Paracetamol tablets prepared with SCMDBS exhibited shorter DT than others but generally all the tablets containing the NDBS and modified DBS also passed the official disintegration time test.



Dioscorea bulbifera starch, pregelatinization, carboxymethylation, sodium carboxymethyl pregelatinized DBS, tablets disintegrant.