The present invention concerns a method for the separation and/or isolation of inhibitors of cellulolytic, xylanolytic and/or beta-glucanolytic enzymes, inhibitors obtainable by said method, and process for obtaining micro-organism, plant or plant material wherein the activity of the inhibitor according to the invention is increased or reduced and to the use of the inhibitor, using the cited micro-organism, plant or plant material and/or the use of endoxylanases selected or modified using these inhibitors in a variety of process and applications.