Platelet nanocrystals resulting from fragmentation of cassava starch granules by acid hydrolysis

K. Kasemwong, K. Laohhasurayotin, I. Samara, W. Kungwansupamongkol, K. Piyachomkwan
National Science and Technology Development Agency, TH

Keywords: acid hydrolysis, cassava starch, crystalline starch, nanocrystals, spherulite starch

Summary:

Nature, perhaps the most talented nanoscientist, has already mastered the synthesis of biological nanomaterials including proteins, lipids and polysaccharides as well as starch granule. This research was conducted to explore the structural and physico-chemistry of nanostructured starch powders (NSP). Nanostructured starch powders were prepared by hydrolyzing granular starch (derived from cassava root; Manihot esculenta) using sulfuric acid and then ultrasonicating in ethanol. Nanostructured starch powders or NSP was named, the remaining starch granules, after acid hydrolysis and characterized the physicochemical properties by XRD, SEM, FTIR and DSC. The crystallinity of nanostructured starch powders increase 80%, compared to native cassava starch. Differential scanning calorimetry (DSC) revealed that a mild hydrolysis for 24 h increased the melting enthalpy of the starch, which might indicate that the hydrolysis was selective in the amorphous regions. Later, at 48–312 h, the hydrolysis rate was higher and remained constant, with gradual increases in DSC melting enthalpy, indicating that the crystalline regions were predominantly. X-ray diffraction patterns revealed the same trend as the DSC results. Average diameter of starch granules or particles was decreased dramatically in both volume- and number-based measurements during the lastly stage of rapid hydrolysis (up to 312 h). The starch fragment of 0.5 µm was assumed to consist of crystalline blocklets.