Properties of granular cold-water-soluble starches prepared at atmospheric pressure

Abstract

Granular cold-water-soluble (GCWS) starches were prepared from wheat, corn, tapioca and a hydroxypropylated cross-linked wheat starch by heating in a 1/1·5/4·5 (w/w/w) mixture of starch, water and propan-1,2-diol (PD). X-ray analysis showed that, immediately after heating, the products were amorphous. Following solvent exchange with ethanol, the prime starches gave a V-type pattern, whereas the modified wheat starch remained amorphous. GCWS wheat starch gave a quantitative yield of D-glucose after digestion with glucoamylase. Light microscopy revealed that GCWS starch granules were fractured internally, but contained an intact shell at the surface. Tiny polygonal bodies, formed by the fractures, refracted light under the microscope, and caused pinpoints of yellow and green colors to show inside the granule. The paste consistencies of GCWS tapioca and hydroxypropylated, crosslinked wheat starches measured at 25 °C in the Amylograph matched those of the starting starches that had been heated in water and then cooled to 25°C, whereas the consistency of GCWS wheat starch was reduced because of incomplete dispersion. GCWS corn starch prepared in aqueous PD versus that prepared in aqueous ethanol required almost twice as long to gel and gave 10% lower gel strength at 7% starch solids in the presence of 16% sugars.