Physicochemical, thermal, pasting and microstructural characterization of commercial Curcuma angustifolia starch

The physicochemical, thermal, pasting and microstructural properties of commercial Curcuma angustifolio starch were analyzed. Scanning electron and light microscopic analyses revealed that the starch granules were polyhedral to round in shape, and were similar to corn starch in appearance. The mean particle diameter was 15.57 mu m at 3% moisture, which increased to 16.79 mu m at 12% moisture content after adsorbing water. Fourier-transform infrared spectroscopy revealed that the 0-C stretching band was double-peaked. X-ray diffractogram manifested mostly `A' type crystalline structures, similar to that of arrowroot and corn starches. The NMR spectrum of this starch also resembled closely that of corn starch, with typical resonances at 100, 71-78 and 60 ppm. The moisture sorption isotherms of C angustifolia starch were sigmoidal shape, with cross over at higher temperature. The glass transition temperature (T-g) decreased linearly from 70.15 degrees C at 3% moisture content to 64.65 degrees C at 12% (R-2 = 0.985) while the peak gelatinization temperature of starch was 78.2 degrees C, with an enthalpy of 20.43 J/g. Thermogravimetric analysis showed that 76% of mass loss related to depolymerization of starch occurred between 275 and 345 degrees C. The derivative curve was single-peaked. Pasting studies showed that C. angustifolia starch showed peak, breakdown and setback viscosities much higher than those of cassava and arrowroot starches. The high phosphorous content conferred high paste viscosity and improved gel strength during pasting. (C) 2016 Elsevier Ltd. All rights reserved.