Grain ultrastructure is of utmost importance when designing grain processing procedures in the food industry. Optical microscopy is widely applied in characterizing cereal grain structures. However, localisation of certain cereal grain components such as arabinoxylan is challenging since specific dyes for staining are lacking. Raman microscopy (Raman imaging or mapping) provides an alternative staining-free microscopic technique to image the distribution of different components in sub-micron resolution in different plant-based samples. However, only a few papers on Raman analysis of cereal grains exist.
Jääskeläinen and colleagues (2013) applied both Optical and Raman microscopy to localise cereal grain components. They found out that optical microscopy was relatively fast and provided the localisation of most of the substances in a relatively large sample area but it requires utilisation of several stains and immunolabeling to localize certain components. Raman spectroscopy, especially when combined with basis spectral analysis, provided a tool to investigate most of the cereal grain components simultaneously. This method did not require any significant sample pretreatment, but the strong fluorescence emission of the substances in the pericarp hindered the Raman studies of these outer layers of the grain. Concluding, Jääskeläinen and colleagues found out that both methods provided consistent information on the grain structures, illustrating the distribution of polysaccharides, aromatics and protein in endosperm and aleurone layers.
Jääskeläinen A-S, Holopainen-Mantila U, Tamminen T, Vuorinen T. Endosperm and aleurone cell structure in barley and wheat as studied by optical and Raman microscopy. J Cereal Sci 2013.
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