ABSTRACT
This study examined growth and control of two enterohemorrhagic Escherichia coli serotype O157:H7 strains in a soft Hispanic type cheese (Queso Fresco). Cheese was made in the laboratory using a commercial procedure and after inoculation it was stored under vacuum at temperatures ranging from 8 to 30 degrees C. The minimum temperature that allowed growth of E. coli in the unmodified normal cheese (pH 6.6) was 10 degrees C. No growth of either strains was observed during a 2 month storage period at 8 degrees C. Accumulated data from the growth studies were used for development of models relating square root of 1/LT (LT = lag time) and specific growth rate, to temperature. The effect of selected antimicrobials (potassium sorbate, sodium benzoate, and sodium lactate) added to milk or cheese on the growth and survival of these pathogens at various storage temperatures was also evaluated. Addition of sodium benzoate (0.3%) to cheese (pH 6.6) or addition of potassium sorbate (0.3%) to cheese (pH 6) made from milk acidified to pH 5.9 with propionic acid, had a significant impact on delaying or preventing growth of the pathogens.
Subject(s)
Cheese/microbiology , Escherichia coli/growth & development , Food Contamination/prevention & control , Animals , Antibiosis , Escherichia coli/drug effects , Food Preservatives/pharmacology , Hydrogen-Ion Concentration , Milk/microbiology , TemperatureABSTRACT
This study evaluated the growth and control of Salmonella serotypes in a soft Hispanic type cheese (Queso Fresco). Cheese was made in the laboratory using a commercial procedure and after inoculation it was stored under vacuum at temperatures ranging from 6 to 30 degrees C. The minimum temperature that allowed growth of Salmonella was 8 degrees C. Accumulated data from the growth studies were used for the development of models relating the square root of 1/LT (LT = lag time) and specific growth rate to temperature. The effect of selected antimicrobials (potassium sorbate, sodium benzoate and sodium lactate) on the growth and survival of Salmonella in milk and in cheese at various storage temperatures was also examined. Addition of sodium benzoate (0.3%) to cheese (pH 6.6) or addition of potassium sorbate (0.3%) to cheese (pH 6.0) made from milk, which was acidified to pH 5.9 with propionic acid, had a significant impact on delaying or preventing growth of the pathogen.
