Distribution of Amygdalin in Apricot (Prunus armeniaca) Seeds Studied by Raman Microscopic Imaging

Amygdalin is a cyanogenic glycoside found in the seeds of several plants belonging to the Rosaceae family. Cyanogenic glycosides can be specifically probed by Raman spectroscopy due to an inherent nitrile group which shows a well resolved band near 2245 cm-1. In the current study the subcellular distribution of amygdalin in thin apricot (Prunus armeniaca) seed sections is probed by high resolution Raman imaging with a step size of 2.5 µm. Further, Raman images and line maps were collected from four apricot seeds with step sizes between 30 and 70 µm. The data were processed by functional group mapping and the spectral unmixing algorithm vertex component analysis. One seed had low amygdalin content in its center and higher content towards its epidermis. The other three specimens showed different distributions of amygdalin, with highest concentration in the center and local concentration spots throughout the seed. We conclude from our Raman image analysis that amygdalin is unevenly distributed in the seed and its location does not follow the same pattern for all seeds. The observed biological variability of the amygdalin distribution cannot be explained satisfactorily yet and requires further investigation.