A thermostable endo-β-D-xylanase (1,4-β-D-xylan xylanohydrolase, EC 3.2.1.8) was purified from the culture filtrate of a thermophilic fungus Thermoascus aurantiacus C436, using a single chromatographic step on SP-Sephadex C50. The purified preparation was homogeneous based on denaturing polyacrylamide and isoelectric focusing gels. The xylanase had a subunit molecular mass of 32 000 daltons, isoelectric point at pH 7.1, apparent Km and Vmax of 0.17% (w/v) xylan and 61.3IU/mg protein, respectively, at 50 °C. The pH and temperature optima for xylan hydrolysis were pH 5.1 and 80 °C, respectively. The xylanase retained full activity following incubation at 60 °C for 97 h or 70 °C for 24 h. At 80 °C, the half-life of the enzyme was 54 min. The xylanase was not affected by copper sulfate, zinc sulfate, calcium chloride, cobalt chloride, barium chloride, magnesium sulfate, and EDTA at concentrations of 2 mM. Mercury chloride at 2 mM concentration abolished all xylanase activity, while lead acetate at the same concentration reduced xylanase activity by approximately 25%. From the initial hydrolysis products of xylan, the xylanase was deduced to hydrolyse xylan through an endo-acting mechanism.

In order to support regulations directed towards ensuring the safety of heat processed dairy products, data on inactivation of alkaline phosphatase (AP) in whole milk in a pilot plant high-temperature short-time (HTST) pasteurizer were obtained. A Computer program was designed to calculate the integrated lethal effect, or pasteurization effect (PE), at temperatures of 60 to 74°C and with holding tubes for 3 to 60 s. An equation was derived which related values of PE to log % residual activity (r2 of 0.964). These results suggest that predictive equations based on PE could be used to assess the effectiveness of commercial pasteurization processes.

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When purified xylanases from Trichoderma harzianum E58 or from a clone of Bacillus circulans were incubated with various low-yield wood pulps, little of the original enzyme activity could be detected in the filtrate at the end of the reaction. Partial bleaching of the pulps prior to enzymatic treatment generally resulted in an increased recovery of the xylanase activity. It appears that both nonspecific adsorption and soluble inhibitors may be responsible for the loss of much of the xylanase activity. However, xylanases from Aureobasidium pullulans and Schizophyllum commune were not as inhibited by the pulps, and the activity of the latter enzyme actually increased after incubation with several high-yield pulps. Although a lignin preparation from spent sulfite liquor at a concentration of 0.06 mg/mL could inhibit the xylanase activity of T. harzianum and B. circulans by 65% and 50%, respectively, xylanases from Thermoascus aurantiacus, S. commune, and A. pullulans were activated at similar lignin concentrations. At higher concentrations these latter xylanases were also inhibited. Water-soluble lignins extracted from a variety of pulps and used at a lignin concentration of 2.5 mug/mL resulted in inhibition of more than 65% of the original activity of the xylanase from T. harzianum. Kinetic studies showed that lignin from spent sulfite liquor resulted in noncompetitive inhibition of this enzyme.