CHARACTERISATION OF SILICIFIED DIOSCOREA DUMETORUM STARCH MODIFIED BY ADDITION OF CHARGED AMINO ACIDS AT VARIOUS PH LEVELS

Oladapo Adewale Adetunji* and Damilola Oluwamayokun Ibrahim

ABSTRACT

Introduction: The use of starches as excipients in drug delivery has led to the modification of starch to improve its functional properties. This study involved two step modification of Dioscorea dumetorum Pax starch (Family: Dioscoreacea) by silicification and co-blending with charged amino acids at various pH levels. The modified starch was characterized and evaluated for its flow and functional properties in comparison with unmodified Dioscorea dumetorum starch (DDS). Methods: DDS was modified by thermal blending with silicon dioxide to yield sDDS. Buffer solutions of pH4 (acetate 0.1M), pH7 (phosphate 0.5M) and pH10 (carbonate 0.05M) were prepared. 20g of sDDS was added into a beaker containing lysine (or aspartic acid) and buffer solution of pH4, pH7 or pH10. The mixture was stirred and dried in the oven at 300C. The dried samples (A-G) were granulated (A=sDDS/lysine/pH4; B=sDDS/lysine/pH7; C=sDDS/lysine/pH10; D=sDDS/aspartic-acid/pH4; E=sDDS/aspartic-acid/pH7, F=sDDS/aspartic-acid/pH10, G=DDS). All samples were characterized using density measurements, flow properties, morphology, Fourier-transform infra-red (FTIR) spectroscopy and pasting properties. The results were analyzed using mean and standard deviation. Results: Bulk and tapped density measurements ranked D>E>F>C>B>A>G and G>B>A>C>D>E>F, respectively, thus indicating that the modification led to a reduction in the spatial volume of the granules. Angles of repose ranked G>C>A>B>D>E>F. Spherical granules were formed by samples A,B,D and E, while others formed irregular shaped granules. FTIR spectra of DDS showed prominent peaks that were retained after modification, but with introduction of more functional groups due to the silicification and amino-acid blending. The peak and breakdown viscosities was ranked D>B>E>F>C>A>G, while the trough viscosity was the reverse. Conclusion: The two-step modification of DDS led to enhanced functional properties of the starch. Granules C and E had better flow and pasting properties respectively, than other granules. Further studies involving modification of the starch using uncharged non-polar amino acids may be carried out.

Keywords: Dioscorea dumetorum starch, Modification, Silicification, Amino acids, Functional properties.