EFFECTS OF TEMPERATURE, A(W) AND PH ON THE GROWTH OF BACILLUS CELLS AND SPORES - A RESPONSE-SURFACE METHODOLOGY STUDY

Effects of water activity (a(w)), pH and storage temperature on the growth of spores and vegetative cells of Bacillus spp. isolated from bakery products were studied in a model system and the growth was monitored spectrophotometrically in microtitre plates. Experiments, performed following a Central Composite Rotatable Design and aimed at development of response surfaces, resulted in two polynomials based mainly on first order coefficients. For both cells and spores, temperature, a(w) and pH acted additively and without any synergistic effect. This was also confirmed by isoresponse plots for the combinations temperature-a(w), temperature-pH and pH-a(w). Applications of the models to predict the shelf life of the actual food product are discussed.