Characterization using Raman microspectroscopy of arabinoxylans in the walls of different cell types during the development of wheat endosperm

The time course and pattern of arabinoxylan deposition in the wheat (Triticum aestivum) endosperm during grain development were studied using Raman spectroscopy. The presence of arabinoxylans (AX) is detected at the beginning of grain filling. At this stage, AX appear more substituted than at the later stages. Feruloylation of AX increases during the grain-filling stage, especially in the case of the aleurone layer. Whatever the stage of grain development, four populations of cells could be defined according to Raman arabinoxylan signatures. In the walls of the aleurone cells, AX appeared to be little substituted and highly esterified with phenolic acids. In the walls of prismatic cells, AX were found to be highly substituted and poorly esterified. Apart from aleurone and prismatic cells, the substitution degree of AX in endosperm was in the same range. Cells in the crease region were distinguished from cells in the starchy endosperm by their lower amount of esterified phenolic compounds.     

Conformational interpretation of vescalagin and castalagin physicochemical properties

Vescalagin and castalagin are two diastereoisomers. The variability of their principal physicochemical properties, compared with their small structural differences, suggests important conformational variations. This study shows, experimentally, that vescalagin has a greater effect on polarity, oxidizability in solution, and thermodegradability than castalagin. Conformational analysis by molecular mechanics demonstrated that vescalagin was more hydrophilic and was more reactive to electrophilic reagents than castalagin. Experimental results were thus explained and demonstrated the distinct behaviors of vescalagin and castalagin. These results were attributed to the C1 position of the two compounds because vescalin and castalin have comparable characteristics. Experimental data were confirmed and interpreted by molecular mechanics. This work represents one of the first attempts to correlate conformation and the properties of phenolic compounds. This step constitutes a predictive method for the pharmacology or chemistry of new compounds.     

Classification of wheat varieties based on structural features of arabinoxylans as revealed by endoxylanase treatment of flour and grain

Arabinoxylans (AX) are cell wall polysaccharides of complex structure involved in many aspects of wheat flour end uses. The study of the variations of AX structure can lead to the identification of genes involved in their biosynthesis, and thus in the control of the various aspects of grain quality related to their presence. A method is proposed to identify AX variations directly in whole grain by enzymatic degradation. An endoxylanase from Trichoderma viride was used to extract AX from a collection of 20 wheat cultivars (Triticum aestivum L.). Enzymatic degradation products were analyzed by HPAEC and multivariate analysis techniques (principal component analysis, canonical correlation analysis, and cluster analysis) were applied to analyze chromatographic data. The method evidenced variations in the proportion of mono- and disubstitution of the xylan backbone by arabinose side chains, allowing classification of the different varieties according to the structural features of AX. A similar classification was obtained starting from flour or whole grain, indicating that the method was specific of AX from endosperm tissues. In conclusion, the method combining endoxylanase treatment of wheat grain and the analysis of degradation products, e.g., enzymatic fingerprinting, can be applied to collections of wheat cultivars, and possibly other cereals in order to establish quantitative trait loci related to the biosynthesis of AX.