Discoloration of industrially important woods causes substantial economic loss. Although color defects are not always associated with structural degradation of wood, they are still a significant problem which negatively affects the applicability, and thus the value, of the wood. It has been proved that during discoloration of wood oxidation and polymerization of phenolic compounds usually occurs, yielding quinones and their oxidized polymers with high molecular weight. The products formed substantially effect not only the color of the wood, but also its durability, processability, and even its mechanical properties. It is therefore necessary to investigate the products formed by the discoloration processes and to invent methods for preliminary chemical indication of possible color defects in living trees and in cut logs. Pedunculate oak occupies 8% of forest sites of Hungary. The most significant type of discoloration, becoming increasingly frequent lately, not only in Hungary but also in Europe, is the so called ‘ring-like discoloration’ of oak heartwood. The causes and the chemical and enzymatic reactions resulting in the discoloration are not yet known. HPTLC separation then qualitative and quantitative scanning densitometry proved to be a rapid, effective, and reliable analytical technique for tracking and identifying the polyphenols associated with the discoloration. From among the tannins present in oak heartwood, gallic acid has been proved to undergo significant changes in concentration in the discolored tissues. The results could contribute to elucidating the causes of the discoloration, working out effective preventative strategies, and enhancing the treatment and utilization of discolored oak wood.
