Crystallite orientation maps in starch granules from polarized Raman spectroscopy (PRS) data

• Orientation maps of crystallites on P. grandifolius starch granules were obtained by PRS.
• Anisotropic response of Raman bands in A-amylose crystals was evaluated.
• Isotropic and highly anisotropic regions were observed in the granules by PRS.

In this work, polarized Raman spectroscopy (PRS) was used to determine orientation maps of crystallites present in Phajus grandifolius starch granules based on the anisotropic response of the glycosidic Raman band at 865 cm−1. The response of this band was preliminarily evaluated using model A-amylose crystals as standard. The A‐amylose crystals oriented “in plane” showed a maximal intensity ratio of ∼3.0 for bands 865/1343 cm−1 when the polarization of the laser was along the chain axis of the crystal, i.e., parallel to the axis of the amylose double helices, and a minimal intensity ratio of ∼0.25 when perpendicular. The orientation maps of Phajus grandifolius starch granules showed two distinct regions: one isotropic and the other with a highly anisotropic response. The origin of the difference might be changes in both organization/concentration and orientation of the crystallites across the starch granules.