Microstructural evolution of wheat kernels during germination: a multi-scale approach

Wheat is one of the most extensively cultivated cereals, with its pre-harvest quality being critical for subsequent food production. In-field sprouting, triggered by sudden climatic changes, alpha-amylase levels in wheat rise, negatively impacting its quality. This study aims to examine germination progression at the microstructural level. Canadian Western Red Spring (CWRS) wheat was germinated under controlled germination conditions for 6, 12, 18, 24, and 36 h. Alpha-amylase activity, the Falling Number, bulk density, starch crystallinity and microstructural analysis by X-ray micro-computed tomography (micro-CT) and scanning electron microscopy (SEM) were measured. The decline in the Falling Number and the rise in alpha-amylase activity confirmed the progress of germination. Bulk density significantly ( p < 0.05) decreased in the germinated kernels, whereas porosity significantly ( p < 0.05) increased after 24-h germination. X-ray micro-CT and SEM images showed considerable structural changes at 36 h of germination. Although no significant differences in the cross-sectional area were observed across the kernels as germination progressed, pores were detected in the kernel crease after 36 h. Likewise, the 36-h germinated sample showed a significantly thicker outer layer in the apical region of the kernel, likely due to the detachment of the outer layer. Notable changes in starch and protein structures were observed after 18 h, while starch crystallinity increased throughout germination. Overall, the results indicate that germination-induced alpha-amylase activity significantly impacts the microstructure of wheat kernels, particularly by increasing the outer layer thickness at the apical part of the kernel. • Germinated wheat kernels have increased open and total porosity compared to sound wheat. • X-ray micro-CT images show the cracks appearing in the crease after 36 h germination. • The thickness of the outer layer increase, especially in the apical part of the kernel. • Detachment of the outer layers and the aleurone appears after 24 h germination. • Enzyme activities generate cavities particularly between germ and endosperm.