The effects of acetylation and pregelatinization on the material and rheological properties of selected botanical starches as pharmaceutical excipients were evaluated. Pregelatinized and acetylated forms of starches of cassava, Manihot esculenta Crantz (Euphorbiaceae) and sweet potato, Ipomoea batatas L. Lam (Convolvulaceae) were prepared and corn starch BP was the standard. The starches were evaluated using physicochemical, microscopic, rheological, FTIR, and X-ray diffraction (XRD) analytical techniques. Microscopic analysis indicated definitive alteration in the granular character of the modified starches. The native starches were susceptible to retrogradation, which was alleviated by acetylation and pregelatinization. Flowability of the starches improved with modification while FTIR and XRD analysis confirmed characteristic functional groups and crystalline morphology of the modified starches. The water absorption and swelling properties of the starches were related to amylose content. Acetylation and pregelatinization of cassava and sweet potato starches significantly altered their granular morphology, rheology, and structure resulting in their improved functionality as potential pharmaceutical excipients.

Starch is an abundant natural polymer with unique properties that make it amenable to various kinds of treatments. This deliberate attempt at altering the character of native starch results in modified starches. Starches are extensively used in the pharmaceutical industry, especially as excipients in tablet formulation. It is now widely acknowledged that starches in their native form have functional limitations. Modification is a means of enhancing the functionality of native starch for a wide variety of applications. The importance of modified starches as excipients for pharmaceutical direct compression has been identified. Although, there is a wealth of information on starch modification, characterization and applications in the literature, there does not appear to be as yet, any attempt at a methodological analysis of physical and chemical modification techniques as they apply to pharmaceutical direct compression. This review aims at addressing these gaps. It describes a range of physical and chemical techniques employed in producing modified starches and their potentials as excipients for direct compression. The effect of modification on the morphological and functional properties of starch in various direct compression formulations is also reviewed.

A B S T R A C TObjective: To investigate the effects of acetylation and pregelatinization of cassava and sweet potato starches on the mechanical and release properties of directly compressed paracetamol tablet formulations in comparison with official corn starch. Methods: The native starches were modified by acetylation and pregelatinization. The tablets were assessed using friability (F r ), crushing strength (C s ), disintegration time (D t ) and dissolution parameters. Results: Starch acetylation produced paracetamol tablets that were stronger and had the best balance of mechanical and disintegration properties, while pregelatinization produced tablets that were more friable but had a better overall strength in relation to disintegration than formulations made from natural starches. Correlations mainly existed between D t and the dissolution parameters t 80 , t 2 and k 1 in the formulations. Conclusions: Modification of the experimental starches improved the mechanical and release properties of directly compressed paracetamol tablet formulations. Thus, they can be developed for use as pharmaceutical excipients in specific formulations.