Abstract

CANAS, Sara et al. Modelisation of Heat Treatment of Portuguese Oak Wood (Quercus pyrenaica L.). Analysis of the Behaviour of Low Molecular Weight Phenolic Compounds. . Ciência Téc. Vitiv. [online]. 2000, vol.15, n.2, pp.75-94. ISSN 0254-0223.

The heat treatment is of primary significance for the barrel quality. In the last fifteen-years many papers have been focused on the effects of heat treatment on the phenolic composition of French and American oak woods, but the oak species grown in Portugal traditionally used in Portuguese cooperage have never been studied. In this study we characterised the toasting levels with temperature and time by modelling, in laboratory, the heat treatment applied to barrels of a Portuguese oak wood (Quercus pyrenaica L.) during coopering. The effect on some phenolic acids and aldehydes was assessed by HPLC. In all toasting levels and throughout the depth, it was found that the best curve to fit the data was given by a 5^th degree polynomial equation. The analysis of phenolic composition indicates that the optimization of this technological operation, in order to maximize the quality of the wood barrels, implies the control of both temperature and time. The results also show that the time has a secondary role in comparison with temperature. The phenolic fraction trends to increase with toasting temperature over time. These effects essentially derive from the increment of ellagic acid and phenolic aldehydes contents, as a consequence of ellagitannins and lignins degradations respectively. Except for ferulic acid, it was observed a decrease of phenolic compounds contents from the surface layer (0 to 2 mm) to the depth layer (2 to 4 mm) of the stave. This could be due to the higher temperature in the surface layer, which certainly causes more intense degradation of the wood constituents, as well as the modification of wood physical and structural properties. Ellagic acid has a more pronounced decrease than the lignin breakdown products throughout the depth, which could indicate that ellagitannins are more affected than lignins.

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