Spectro-topochemical investigation of the location of polyphenolic extractives (tannins) in chestnut wood structure and ultrastructure
2019
Giovando, S. | Koch, G. | Romagnoli, M. | Paul, D. | Vinciguerra, V. | Tamantini, S. | Marini, F. | Zikeli, F. | Scarascia Mugnozza, G.
Tannins are an important industrial product, with chestnut being one of the most representative species for their production, due to the occurrence that the species possesses within its wood quite big amounts of hydrolysable tannins. For industry, it is quite important to know at the cellular level where tannins are located – in the cell lumen or cell wall – and the efficiency of a particular tannin extraction process. The objective of this study was to identify and locate tannins in chestnut wood by means of UMSP (UV microspectrophotometry), considering both shoots and standards in coppice stands. The analyses were also carried out in standards before and after tannin extraction according to the parameters and methodology of an industrial process. Tannins were localized mainly inside the cell lumen of parenchymatic cells and vessels, and they were visible in parts adjacent to the cell walls. In shoots, they have been found also in locations where the cell wall is degraded. In the standards, tannins with more UV absorbance were detected and evidently present in the corners of wood cells. After tannin extraction, the cell lumen was empty, but tannins, even with lower absorbance values, were still present, mainly in the cell corners. The results open up discussion on the utilization of residual wood flour as a by-product after initial tannin extraction, which could be further exploited from the overall perspective of a circular economy.
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