PREDICTIVE MODEL TO DESCRIBE THE COMBINED EFFECT OF PH AND NACL ON APPARENT HEAT-RESISTANCE OF BACILLUS-STEAROTHERMOPHILUS

The combined effect of pH and NaCl on the apparent thermal resistance of Bacillus stearothermophilus ATCC 12980 spores was studied. Spores w ere heated at different temperatures (115-125 degrees C) in mushroom s ubstrate, acidified using glucono-delta-lactone to different pH levels (from 5.75 to 6.7), which contained concentrations of NaCl that range d from 0.5 to 3% (w/v). The recovery medium was acidified to the same pH level and contained the same NaCl concentration as the heating mens truum. A factorial experimental design allowed a predictive model to b e developed, which described the combined effect of heating temperatur e, pH and NaCl on the thermal resistance of B. stearothermophilus spor es. Predictions from the model provided a valid description of the dat a used to generate the model, and agreed with observations from the li terature and from an independent experiment performed using asparagus and bean substrates. (C) 1998 Elsevier Science B.V. All rights reserve d.