Four new bacterial xylanases from different glycosyl hydrolase families (11, 10 and 5) were evaluated for hexenuronic acid (HexA) removal capacity and bleach boosting ability of a eucalypt kraft pulp. The family 11 xylanase was the most effective in enhancing HexA removal and also in increasing delignification and brightness. A very innovative point was that a xylanase from family 5 was applied in pulp bleaching for the first time, showing a notable contribution to pulp bleachability. On the contrary, the family 10 xylanases did not modify kappa number or brightness. A remarkable effect was that the tested xylanases reduced pulp HexA content. The effects produced by the different xylanases in pulp properties were closely related with the effects observed in the effluent properties. The effluents from enzymatic treatments showed the dissolved xylans and xylooligosaccharides branched with HexA, as well as lignin. In addition, a simple tool to assess the boost bleaching ability of a xylanase treatment was also used.

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