Small-angle X-ray scattering measurements of gel produced from α-amylase-treated cassava starch granules

Cassava starch granules slightly hydrolyzed by alpha-amylase from Aspergillus niger show significantly enhanced gelling properties (Ichihara, Fukuda, Takaha, Yuguchi, & Kitamura, 2014). This paper investigates the mechanism of these enhanced gelling properties by dynamic viscoelastic analysis and small-angle X-ray scattering (SAXS). The storage modulus (G') of alpha-amylase-treated cassava starch paste was greater than that of native cassava starch paste, and the tan delta (G ''/G') of the treated paste was almost zero at the tested angular frequency, which is much lower than for native cassava starch. The SAXS results suggest that the microscopic gel structure is composed of highly aggregated inhomogeneous nano-scale structures and diluted regions of single and helical amylose chains. Starch crystallization and growth of aggregates were faster, and the size of aggregates larger, for alpha-amylase-treated cassava starch than for native starch. These results further support our hypothesis that alpha-amylase treatment improves the elasticity of starch gel by constructing a strong filler-in-matrix type structure. (C) 2015 Elsevier Ltd. All rights reserved.