Three strains of the thermophilic fungus Thermomyces lanuginosus were used to produce beta-xylanases. The thermal stability of these xylanases at low levels of water activity was studied. Isothermal inactivation experiments were performed in the temperature range of 100-130 degrees C. Reduction of water activity to 0.63 and as low as 0.13 had a drastic effect on the observed D and z-values. At water activity of 0.13 the D(120 degrees C) and z-values of the three xylanases ranged from 20.4 to 37.6 min and from 23.3 to 28.9 degrees C, respectively. The applicability of the developed kinetic models was tested under time-temperature profiles representative of typical thermal processes. The developed systems can be applied as time-temperature integrators (TTI) at this high thermal processing range. Calculations demonstrated that the use of a triple xylanase TTI system could provide acceptable F-values prediction for z-values lower than the achieved range. (C) 2010 Elsevier Ltd. All rights reserved.