Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/2/2007
Publication Date: 12/1/2007
Citation: Abou-Zeid, K.A., Yoon, K.S., Oscar, T.P., Schwarz, J.G., Hashem, F.M., Whiting, R.C. 2007. Survival and growth of Listeria monocytogenes in broth as a function of temperature, pH, and potassium lactate and sodium diacetate concentrations. Journal of Food Protection. 70(11):2620-2625. Interpretive Summary: Listeria monocytogenes is an opportunistic human bacterial pathogen of food origin that causes illness in certain high risk groups including pregnant women, neonates, and immunocompromised adults, but may occasionally cause illness in persons with no predisposing underlying conditions. Due to the severity and case-fatality rates (20 to 25%) of listeriosis in the highly susceptible human populations, the development of control measures for this pathogen is of major interest to the food industry. Sodium and potassium lactates and sodium diacetate salts have been recognized as safe additives to different meat products. They are already widely used in the food industry to extend the shelf-life and increase the safety of meat and poultry products by reducing survival and growth of spoilage and pathogenic bacteria. A rather new development in the field of food safety is the use of a combination of sodium or potassium lactate and sodium diacetate to control pathogens, such as Listeria monocytogenes. In this study, the effect of a commercial mixture (PURASAL P Opti.Form 4TM) of potassium lactate and sodium diacetate on the survival and growth of Listeria monocytogenes in laboratory broth formulations was investigated. Inhibitory effects of PURASAL P Opti.Form 4TM on the growth and survival of the pathogen were observed in all laboratory broth formulations investigated with the most pronounced inhibition in broth formulations that simulated low pH meat and poultry products stored at cold temperatures. Results of this study suggest that PURASAL P Opti.Form 4TM can be introduced as a substantial hurdle to the survival and outgrowth of Listeria monocytogenes in meat and poultry products stored at a range of temperatures.
Technical Abstract: The objective of this study was to determine the antimicrobial effect of a combination of potassium lactate and sodium diacetate (PURASAL P Opti.Form 4TM, 60% solution) on the survival and growth of Listeria monocytogenes Scott A in pH adjusted broth (5.5, 6.0, 6.5 and 7.0) stored at 4, 10, 17, 24, 30 and 37C. Appropriate dilutions of broth were enumerated by spiral plating on tryptose agar and counting with an automated colony counter. Growth data were iteratively fit using non-linear regression analysis to a three-phase linear model using GraphPad PRISM software. At pH 5.5, the combination of lactate and diacetate fully inhibited (P< 0.001) the growth of L. monocytogenes at all tested levels and temperatures. At pH 6.0, addition of 1.8 % lactate and diacetate reduced (P<0.001) the growth rate of L. monocytogenes and decreased the lag time period; however, 3% and 4.5% completely inhibited the growth at the six temperatures studied. Efficacy of the lactate and diacetate mixture was reduced as pH and incubation temperature increased. Thus, at pH 6.5, at least 3.0% was required to reduce (P<0.001) the growth of L. monocytogenes. There was a limited effect of the lactate and diacetate mixture on the growth rate of the pathogen at pH 7.0. However, 1.8 and 3.0% significantly lengthened the lag time at 4 and 10 degree C. These results suggest that 1.8% of lactate and diacetate mixture can be used as a substantial hurdle to the growth of L. monocytogenes at pH of 5.5 and 6.0, but at least 3.0% of the lactate and diacetate mixture is needed to reduce growth of L. monocytogenes at pH 6.5. These data will be used to develop a predictive model for growth of Listeria monocytogenes in broth as a function of lactate and diacetate concentration, pH, and temperature.