Evaluation of Starch from Ghanaian Sweet Potato Varieties as Excipients for Solid Oral Dosage Forms

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The study sought to investigate the functional properties of starches obtained from four (4) new Ghanaian sweet potato varieties, in order to facilitate their exploitation as substitute excipients for the local pharmaceutical manufacturing industry. The varieties, namely: CRI Hi-starch, Sauti, Ogyefo and Faara were developed by way of introgression of desirable genes into adapted local germplasm, while their respective starches were obtained by wet separation techniques. Organoleptic properties ofthesweet potato root tubers and their starches, in addition to pre-formulation studies on the starches’ physicochemical properties, proximate composition and pasting properties were undertaken in order to determine their suitability for pharmaceutical use. Furthermore, validation studies onthe sweet potato starches were carried out in order to determine their performance as pharmaceutical binder and disintegrant. Differences in the physicochemical properties, proximate composition, pasting properties and functional properties (as binder and disintegrant)for the four sweet potato starches were not significant. The Hi-starch sweet potato variety however had substantially high starch yield on fresh and dry weight basis (31.7 % fwb; 79.9 % dwb) and may becommercially suitable for industrial exploitation. Starches from all four sweet potato varieties were white in colour and predominantly fine (particle size < 75 µm). Granule shape of the sweet potato starches ranged from round to polygonal with mean diameter in the range of 14.2 - 16.3 µm. The sweet potato starches had higher bulk density (0.50 - 0.58g/cm3), tapped density (0.75 - 0.82 g/cm3) and true density (1.15 - 1.18g/cm3) compared to a commercially available maize starch (0.40, 0.61 and 1.10g/cm3, respectively). The sweet potato starches also had acidic pH (5.1 - 5.9), lower amylose content (22.3 - 26.2 %) and higher purity (97.37 - 97.84 %) compared to the commercial maize starch (5.2, 27.6 % and 96.82 %, respectively). Starch from all four sweet potato varieties had a ‘type A’ pasting pattern; which was characterized by a high swelling power, maximum granule fragmentation, low setback and final viscosities. The swellingcapacity of the sweet potato starches (694 - 762 BU) was comparable to that of a commercially available ‘super disintegrant’ [sodium starch glycolate (762 BU)], but higher than that of the commercial maize starch (451 BU). The tensile strength (tablet hardness) and friability of paracetamol tablets formulated with the sweet potato starches as binder were significantly better (p < 0.05) than similar compacts containing the commercial maize starch. The sweet potato starches also caused faster tablet disintegration and release of paracetamol. The results established thesweet potato starches to be suitable for pharmaceuticaluse andthey were more robust as binder and disintegrant compared to the commercially available maize starch.
A Thesis submitted to the Department of Pharmaceutics, Kwame Nkrumah University of Science and Technology, in partial fulfillment of the requirements for the degree of Master of Philosophy, January-2013