ELUCIDATION OF FACTORS INVOLVED IN THE FORMATION OF WESTERN HEMLOCK SAP BROWNING

Brown discolorations which occur in western hemlock, were investigated because they periodically cause great economic loss in the Canadian e xport lumber markets. In this study some factors involved in browning of western hemlock sap samples were determined in vitro. It was demons trated that oxygen is essential to the production of browning in sampl es of western hemlock sap. Furthermore, brown colorations were produce d in vitro in western hemlock sap samples when heated and when incubat ed at pH 7 or with fungi. Enzymes present in western hemlock sap seeme d not to be involved in the browning process. Stabilization of the sap pH in the acid range effectively controlled sap browning induced by f ungi. Catechin played a major role in the browning process but other s ap constituents must contribute to the coloration. Based on the findin gs made in this study chemical treatments and vacuum kiln-drying are b eing investigated as means to control the production of hemlock browns tain. Furthermore, fundamental research is underway to better understa nd the chemistry/biochemistry of hemlock brownstain.