Thermal resistance of Bacillus stearothermophilus spores has been established inoculating spores in alginate-mushroom puree mixture (ungelled) and in alginate-mushroom puree mixture set in calcium chloride (gelled). Data are compared with those obtained suspending the spores in distilled water, mushroom extract and in calcium chloride. Results indicated that, in general, D values obtained in gelled mixture were higher than D values obtained in distilled water, mushroom extract or in ungelled mixture, while the D value in the ungelled mixture was similar to that obtained in distilled water. D121 value in gelled mixture was close to that obtained in 2% (w/v) calcium chloride.