Preparation and characterization of retrograded cassava starch and its evaluation as directly compressible excipient
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Date
2017-01
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Addis Ababa Universty
Abstract
Starch is a semi-crystalline biopolymer that serves as a carbohydrate reserve in many plants,
including cereals, roots, tubers, seeds, and fruits. Starch granules can vary in shape, size,
structure, and chemical composition, depending on the origin of the starch. In recent years
among polysaccharides, starch is receiving utmost attention due to its usefulness in different
industrial products. Unprocessed native starches are structurally weak and functionally restricted
for application in pharmaceutical, food and non-food technologies. Modifications are necessary
to create a range of functionality. Modification can be, physical, chemical or enzymatic.
Starch was isolated from Cassava (Manihot esculenta), gelatinized in the presence of water then
allowed for retrogradation. Some of the physicochemical properties of the retrograded cassava
starch such as densities, flow, swelling power, solubility, moisture sorption were determined and
compared to those of native cassava starch and Starch 1500®. Compactability was determined
through volume reduction of the powder under tapping for Kawakita analysis and volume
reduction mechanism under compression pressure for Heckel plot. The comparative direct
compressibility and magnesium stearate sensitivity of these starches in tablet formulations were
also studied and the resulting tablets were evaluated for their physico-mechanical properties.
The results of flow and compactability studies of the retrograded starch powder (angle of repose,
Carr’s index (CI) and Hausner ratio (HR), and Kawakita analysis) indicate that retrogradation
improved both flow and compactability of the modified cassava starch. Retrograded cassava
starch showed angle of repose below 30, CI below 16, HR below 1.25, and flow rate of 8.23 ±
0.227 (g/s). In moisture sorption study, retrograded cassava starch exhibited relatively higher
moisture sorption pattern than the native form. Retrogradation also increased the swelling power
of the native cassava starch. The small “a” values of the Kawakita constant (indicating good
fluidity) supported the fact that modification of the starch improves the powder flowability.
Heckel plot was used as assessment parameter where the Py, D0, DA, DB variables were
investigated. Retrograded cassava starch depicted lower Py value than Starch 1500® owing to a
higher plastic deformation. Retrograded cassava starch showed higher sensitivity to magnesium
stearate than starch 1500®.From the foregoing it can be concluded that retrograded cassava starch has the potential to be
used as an alternative directly compressible excipient as it exhibits good flow and compaction
properties.
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Keywords
Cassava Starch; Retrogradation; Directly Compressible Excipient; Magnesium Stearate Sensitivity.