PREDICTION OF LISTERIA SPP. GROWTH AS AFFECTED BY VARIOUS LEVELS OF CHEMICALS, PH, TEMPERATURE AND STORAGE TIME IN A MODEL BROTH

The effects of concentration of NaCl (0.5 to 12.5%), methyl paraben (0 .0 to 0.2%), sodium propionate (0.3%), sodium benzoate (0.1%), potassi um sorbate (0.3%), pH ( > 5.9) temperature (4 to 30 degrees C), storag e time (up to 58 d) and inoculum ( > 10(5) to > 10(-2) per ml) on the log(10) probability percentage of one cell of Listeria spp, to initiat e growth in a broth system were evaluated in a factorial design study. At pH 5.96 and temperature ranging from 4 to 30 degrees C the concent rations of sodium propionate, potassium sorbate, and sodium benzoate e xamined allowed growth of L. monocytogenes with lag phases at 4 degree s C of 18, 27 and 21 days, respectively. For 0.1 and 0.2% methyl parab en growth of all Listeria spp. was initiated at 8 degrees C and 30 deg rees C, respectively. At pH 6, concentration of 12% NaCl supported the growth of L. monocytogenes at 8 to 30 degrees C, whereas 12.5% inhibi ted all Listeria species. Four regression equations were derived relat ing probability of growth initiation to temperature, concentrations of NaCl and preservatives storage time, and Listeria species specific ef fects. From these equations, the number of cells needed for growth ini tiation can be calculated. The impact of this type of quantitative stu dy and its possible application on the development of microbial standa rds for foods is discussed. Published by Elsevier Science B.V.