Surface structure and water adsorption behavior of waxy/amylose extender (wx/ae) double‐mutant rice starch

Abstract

We studied the surface structure and water adsorption behavior of waxy/amylose extender (wx/ae) double‐mutant rice starch using scanning electron microscopy, nitrogen gas adsorption, and water adsorption capacity analysis under various relative humidity conditions, and the nature of the bound water in the starch by differential scanning calorimetry. The wx/ae starch sample had a specific surface area of 3.26 m2/g and pores on its surface with diameters ranging from 6 to 60 nm. Its water adsorption capacity was 0.278 of the weight fraction of water and its weight fraction of bound water molecules was 0.233, both of which are larger than those of wx and wild‐type (WT) starches. We suggest that the starch–water interaction is primarily determined by the morphology and nanostructure of the starch, such as the granule shape and size, specific surface area, porosity, and crystal structure, and that wx/ae starch has a greater capacity to interact with water molecules because of its unique structure.

Selective Adsorption of Essential Oil Compounds by Waxy/Amylose Extender (wx/ae) Double‐Mutant Rice Starch Revealed by Gas Chromatography

“…The surface structures of wx/ae and wx starch granules are different. The specific surface area of the former (3.26 m 2 /g) is about 80% larger than that of the latter, with many more pores on its surface; wx starch granules show mostly a smooth surface without pores . The relationship between the surface structure of starch granules (and their derivatives like dextrin) and the adsorption properties of other compounds has been studied before.…”

“…These conditions were decided by using technical information from GL Science Inc. Table 1. Summary of structural and physical properties of wx/ae and wx rice starches [3][4][5] . www.advancedsciencenews.com www.starch-journal.com…”

“…One of these mutants is the rice double mutant waxy/amylose extender ( wx/ae ) with defective granule‐binding starch synthase (GBSSI) and starch branching enzyme b (BEIIb). We found that wx/ae starch had unique structural and physical properties summarized in Table . It consists only of amylopectin with long unit chains, has B type crystallinity and is indigestible by α‐amylase .…”

“…It consists only of amylopectin with long unit chains, has B type crystallinity and is indigestible by α‐amylase . A larger surface area and more pores on its surface than wx starch give it greater water‐binding capacity than wx starch . We expect that wx/ae rice starch will be useful as an adsorbent for chemical compounds.…”

“…We found that wx/ae starch had unique structural and physical properties summarized in Table 1. [3][4][5] It consists only of amylopectin with long unit chains, has B type crystallinity and is indigestible by α-amylase. [4] A larger surface area and more pores on its surface than wx starch give it greater water-binding capacity than wx starch.…”