Sterols extraction from bark

Terpenes, especially triterpenes, are major components of extractives from barks (104, 292, 388). Among the most commonly reported major triterpenes are a- and 5-amyrin, betulin, friedelin, cycloartenol lactones, ursolic acid, oleanolic acid, serrantendiols, and sterols (see Chap. 8). 

All these lipophilic components perform a function for the living tree. The exact function is not understood for all substances. The composition of the lipophilic wood extractives varies from species to species, and is far from homogeneously distributed in the tree. All woods contain sterols, waxes, glycerides and other aliphatic extractives. However, softwood contains considerable quantities of rosin acids (e.g. abietic acid), but these acids do not exist in hardwood (e.g. birch and aspen). Certain components are predominantly located in the bark of the tree. The sterol fraction from birch and aspen bark comprises almost exclusively beta-sitosterol by way of example. 

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