A further study on supramolecular structure changes of waxy maize starch subjected to alkaline treatment by extended-q small-angle neutron scattering

Abstract

Recently, we reported the effect of mild alkaline treatment on the structure and enzymatic hydrolysis of waxy maize starch. Here, we have used extended-q small-angle neutron scattering (SANS) to examine the extent to which this treatment causes structural changes on even greater length scales — to yield a complete picture from the nanometre to micron — including on the lamellar distribution and larger-scale structural features of the same starch. For this A-type polymorph starch containing mostly amylopectin, we found the changes caused by NaOH solution treatment (0.1% or 0.5% (w/v)) were confined mainly to double helices and crystallites, whereas the lamellar and supramolecular structures were conserved. Although the overall lamellar ordering was reduced in the 0.5% (w/v) alkaline treatment for 6 days, further treatment until 12 days could restore the overall lamellar ordering. Despite changes in starch double helical order and crystallites, there were minimal changes at larger length scales (e.g., blocklets and growth rings). This combination of methods reveals the extent of structural changes occurring as a result of mild alkaline treatment of waxy maize starch; it also provides insight into the rational design of granular starch products with varied functionality via hydrolytic control.