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 gr owth of spores and vegetative cells of Bacillus spp. isolated from bak ery products were studied in a model system and the growth was monitor ed spectrophotometrically in microtitre plates. Experiments, performed following a Central Composite Rotatable Design and aimed at developme nt of response surfaces, resulted in two polynomials based mainly on f irst order coefficients. For both cells and spores, temperature, a(w) and pH acted additively and without any synergistic effect. This was a lso 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.