Structural and chemical analysis of native and malted barley kernels by polarized Raman spectroscopy (PRS)

• Native and malted barley kernels were studied by polarized Raman spectroscopy.
• Band-target entropy minimization resolved six spectra in barley kernels.
• Reconstructed images revealed the chemical changes of barley kernels upon malting.
• Raman anisotropic response of barley starch granules was analyzed.

In this work, barley kernel sections embedded in resin were mapped using polarized Raman spectroscopy (PRS) for evaluation of both chemical and structural changes in endosperm upon malting. A multivariate analysis that includes Band-Target Entropy Minimization (BTEM) was used to resolve the individual spectrum of components present on sections and to reconstruct images based on their relative signal. BTEM-resolved spectra matched with several individual model compound spectra that allowed the identification of protein, starch, non-starch carbohydrates, esterified ferulic acid and embedding media. Raman images also revealed chemical changes in the cell walls within starchy endosperm and inside cells due to enzymatic reactions in malting. The anisotropic response of the C–O–C Raman band associated with the orientation of ordered structures inside starch granules remains despite a notorious shape distortion of large starch granules.