[Change in composition of structural components of leaf cellulose sulfate during fermentation bleaching by xylanases]. 
The possibility of the use of xylanase preparations for hydrolysing hemicelluloses in a non-bleached kraft pulp in order to facilitate its bleaching was studied.  The effects of enzymatic preparations of the fungal and bacterial origins were examined, and the optimal conditions for xylanase activity were determined.  UV spectroscopy demonstrated that the treatment of kraft pulp with the enzymatic preparations containing xylanase facilitated the subsequent removal of lignin and increased the brightness by 5%.  The effect of enzymatic treatment was retained in the case of peroxide bleaching.  The enzymatic preparations studied are promising for the development of chlorine-free pulp bleaching technologies.