GROWTH KINETICS OF LISTERIA MONOCYTOGENES IN SOYMILK OF VARYING INITIAL pH AND SUGAR CONCENTRATIONS

ABSTRACT The ability of Listeria monocytogenes to grow at 5–30C in soymilk of varying initial pH (6.0–6.8) and sugar concentration (0.5–10%, w/w) was challenged using a cocktail of three hemolysin positive strains of the microbe. Growth was determined using trypticase soy agar plus yeast extract and the data were analyzed using Gompertz equation to generate lag phase duration (LPD), exponential growth rate (EGR), generation time and maximum population density values. The result indicated that soymilk is a favorable medium for the growth of L. monocytogenes. The growth kinetics was dependent on interactions of temperature, pH and sugar concentration. Increase in temperature, initial sugar level and pH significantly reduced LPD and increased EGR. Since the microbe is a highly heat‐resistant vegetative pathogen, there is the need for effective control of the processing and handling of soymilk especially at household level to prevent possible incidence of listeriosis through the product. PRACTICAL APPLICATIONS Listeria monocytogenes growth data could provide vital information for risk assessment of the pathogen in soymilk. Such data are necessary for establishment of guidelines for the product safety and inspection purposes.