Concentrations of carbon (wheat bran), and nitrogen (soybean flour) sources, mineral salts (KH₂PO₄, MgSO₄ i CaCl₂) as well as pH of culture medium and time of cultivation were optimized within the scope of the presented work to achieve the highest yield of endoxylanase biosynthesis. Conditions of production of A. niger IBT-90 xylanase preparation with a very low cellulolytic activity and hence useful for bread-making, were optimized according to Box and Wilson [Box i Wilson, 1951]. For this purpose, two successive sets of experiments, i.e. factorial and gradient optimization procedures were carried out. In the former experiment, the linear increase in endoxylanase activity, achieved for subsequent variants of culture medium composition throughout its gradient optimization, indicated that optimum culture medium composition was not found. The latter was determined on completion of the second set of experiments and approximation of its results. Optimization of A. niger IBT-90 culture conditions resulted in 3 fold rise in the endo-1,4-β-xylanase activity (from 84.5 to 254.3 U·cm^-3) as compared to the activity observed at initial conditions. The activity of endoglucanase in the obtained preparation was low (1.5 U·cm^-3).

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