Reaction patterns of wheat starch granules substituted with an anionic propylene oxide analog (POA) revealed by confocal microscopy and 3D anaglyph imaging

A technique was developed for investigating granular reaction patterns of anionic starch derivatives, utilizing the optical sectioning capability of reflectance confocal laser scanning microscopy in combination with 3D anaglyphic imaging (3D glasses required for visualization). The method facilitated improved visualization of internal granular reaction patterns by discarding optical sections comprising the highly-reacted external granule surface (generating 3D image constructs from sections constituting exclusively internal regions of granules) and minimizing confounding background signal associated with non-starch constituents (e.g., proteins). For wheat starch A-type granules substituted with a propylene oxide analog (POA), granular reaction patterns revealed that reagent reached the hilum region of granules through channels, and primarily entered the granule matrix via lateral diffusion from channel surfaces, producing relatively homogeneous reaction patterns. The homogeneous nature of POA granular reaction patterns was attributed to the relatively low reactivity of the reagent (rate of diffusion > rate of reaction).