Common wheat (Triticum aestivum L.): evaluating microstructural changes during the malting process by using confocal laser scanning microscopy and scanning electron microscopy

Abstract

Confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) were used to investigate the microstructural changes in wheat (Triticum aestivum L.) during the malting process. With the help of these powerful optical tools, the organization of starch, proteins and cell walls of cereals could be investigated separately in projections and the microstructure was visualized with an imaging software. Both microscopes were necessary for the investigation and the evaluation of microstructural changes, because SEM and CLSM have different merits and optical benefits. CLSM achieves an overview of single compounds of the grain, which can be used to quantify them. On the other hand, SEM has a higher magnification, where a deeper insight in the kernel structure could be obtained. In particular, the surface of starch kernels can be visualized, when they get degraded by enzymes. Furthermore, a detailed starch structure can be monitored by using SEM. Various grain regions, such as aleurone layer, starchy endosperm and germ, were visualized with the CLSM, and differences in the single fractions were clearly visible. Starch in unmalted cereals revealed that it is embedded in a compact protein network, which consists of protein bodies and is degraded during the malting process. Also the cell walls, mainly consisting of β-glucan, are clearly visible in the unmalted stage and get more and more degraded during the malting process. Hence the differences in the overall structure of unmalted to malted grains were investigated by CLSM and SEM and verified using established malt analysis.