Eucalyptus globulus wood and pulp localization pof sterols involved in pitch deposition using filipin fluorescent staining

Abstract

Sitosterol is one of the main compound found in pitch deposits during totally-chlorine free (TCF) bleaching of Eucalyptus globulus kraft pulp. Filipin staining was used for the first time as a selective method to localize sitosterol in eucalypt pulp and wood. This polyene antibiotic reacts specifically with several 3-hydroxysterols, such as sitosterol representing 72% of total sterols in E. globulus wood, forming fluorescent complexes. Filipin staining showed sitosterol in the walls and lumen of rays parenchyma cells. Distinct fluorescence was observed also in the bordered pits of fibers, as well as in tyloses occluding vessels. In general, the different wood elements in pulp retained the filipin reaction pattern observed in wood, but fluorescent aggregates were found on the surface of unbleached fibers. Parenchyma cells in pulps showed fluorescent pits especially at their stubby ends. A significant removal of sitosterol from the different pulp elements was observed after TCF bleaching.