Structural changes during starch pasting using simultaneous Rapid Visco Analysis and small-angle neutron scattering

Rapid Visco Analysis (RVA) is an industry-wide method extensively used for determining the viscous properties of starch slurries enabling information to be extracted on pasting properties; however little is known about structural changes that occur during standard protocols. A commercial RVA instrument was modified to allow the passage of a neutron beam through its heating block and paddle assembly to enable the simultaneous measurement of SANS and RVA on a variety of commercial starches. SANS measurements were made at 1 min intervals throughout a standard 13 min RVA process across a q range of 0.018–0.2 Å−1. In each of the starches, the well-known lamellar structure was observed up to the point at which the viscosity began to increase markedly. At this stage, the lamellar structure transformed instantaneously; the scattering patterns are indicative of the formation of a large scale structure with no apparent semi-crystalline properties and whose spatial arrangement may be analysed in terms of a fractal-like gel. The basic building blocks of this gel, under the assumption that they are spheroidal, appear to have dimensions of approximately 1 nm across all the starches tested. The sizes of the aggregates formed are several times larger and were found to vary across the time course of the experiment.

► First simultaneous Rapid Visco Analysis and small-angle neutron scattering study.
► Lamellar structure observed in commercial starches up to viscosity increase point.
► Structure transformed to larger dimension with loss of lamellae.
► Structure analysed as fractal-like gel with ca. 1 nm building blocks.
► Aggregates formed vary with time; increased aggregate dimensions correlate in general with increased viscosity.
► Aggregates formed are larger and vary with time; increased aggregate dimensions correlate with increased viscosity.