THERMAL INACTIVATION OF BACTERIA - A NEW PREDICTIVE MODEL FOR THE COMBINED EFFECT OF 3 ENVIRONMENTAL-FACTORS - TEMPERATURE, PH AND WATER ACTIVITY

An empirical, linear-Arrhenius model for predicting the combined effec t of three environmental factors on the thermal inactivation (i.e. dea th) rate of Escherichia coli, namely inactivation temperature, pH and water activity (a(w)), is synthesised from published, and independent experimental data. For inactivation rates obtained both at isothermic condition, a constant temperature of 58 degrees C, with a seven level pit range (pH 3 to pH 9), and a three level range of values of a(w) (0 .928 to 0.995); and anisothermic conditions (a range of inactivation t emperature 52.05 to 63.10 degrees C, with a four level pH range of bet ween pH 3 to pH 9, and a three level range of a, from 0.928 to 0.995), the model gave a very high degree of fit. The synthesised model is qu adratic in form. For isothermic inactivation the model has three terms (pH, pH(2), and a(w)(2)) and explained 96.7% of the variance accounte d for (% V) in the overall data (i.e. seven levels of pH and three lev els of a,). The model with four terms (1/T, pH, pH(2), and a(w)(2)) ex plained 80.7 % V in the overall anisothermic data, and between 90.1 an d 95.3 % V at each level of a(w). Comparison with an existing model hi ghlighted the advantages of the newly synthesised model including ease of formulation, and ease of use. The new model form should permit rea dy integration with equations describing the viscous and thermal prope rties in design for batch or continuous steriliser design. Findings su ggest an additive linear-Arrhenius model is applicable to the combined influence of n environmental factors on the thermal inactivation rate . Copyright (C) 1996 Canadian Institute of Food Science and Technology . Published by Elsevier Science Ltd