Polyphenols and Colour of Douglas Fir Heartwood

Heartwood Colour Dihydroquercetin Leucocyanidin Summary The natural red-orange colour of Douglas fir heartwood limits its utilization for the production of thermo-mechanical pulps. Heartwood colour, determined in the CIEL*a*b* system, is studied in relation to various treatments applied to the wood. Heartwood differs from sapwood by the presence of poorly extractible pigments, fairly resistant to hydrogen peroxide bleaching. A model experiment suggests that they are formed by the enzymic reduction of dihydroquerce tin, the main extractive of Douglas-fir heartwood. The resulting unstable leucocyanidin spontaneously auto-oxidizes to polymeric pigments similar to those found in heartwood.