Survival and growth of Listeria monocytogenes in broth as a function of temperature, pH, and potassium lactate and sodium diacetate concentrations.
The objective of this study was to determine the antimicrobial effect of a combination of potassium lactate and sodium diacetate (0, 1.8, 3, and 4.5%; PURASAL P Opti. Form 4, 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 37 degrees C. Appropriate dilutions of broth were enumerated by spiral plating on tryptose agar and counted with an automated colony counter. Growth data were iteratively fit, using nonlinear regression analysis to a three-phase linear model, using GraphPad PRISM. At pH 5.5, the combination of lactate-diacetate fully inhibited (P < 0.001) the growth of L. monocytogenes at all four levels and six temperatures. At pH 6.0, addition of 1.8% lactate-diacetate reduced (P < 0.001) the specific growth rate of L. monocytogenes and increased lag time; however, 3 and 4.5% completely inhibited the growth at the six temperatures studied. Efficacy of the lactate-diacetate mixture was decreased as pH increased and incubation temperature increased. Thus, at pH 6.5, at least 3% was required to retard (P < 0.001) the growth of L. monocytogenes in broth. There was a limited effect of the lactate-diacetate level on the specific growth rate of the pathogen at pH 7.0. However, 1.8 and 3% significantly lengthened the lag time at 4 and 10 degrees C. These results suggest that 1.8% of lactate-diacetate mixture can be used as a substantial hurdle to the growth of L. monocytogenes when refrigerated temperatures are maintained for products with pH less than 6.5.
Center for Food Science and Technology and, U.S. Department of Agriculture, Agricultural Research Service, University of Maryland Eastern Shore, Princess Anne, Maryland 21853, USA.
K A
KA
Abou-Zeid
K S
KS
Yoon
T P
TP
Oscar
J G
JG
Schwarz
F M
FM
Hashem
R C
RC
Whiting
D015169:Colony Count, Microbial; D003470:Culture Media / Q000737:chemistry; D004305:Dose-Response Relationship, Drug; D005511:Food Handling / Q000379:methods*; D005516:Food Microbiology; D005519:Food Preservation / Q000379:methods*; D005520:Food Preservatives / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007773:Lactates / Q000494:pharmacology*; D008089:Listeria monocytogenes / Q000187:drug effects / Q000254:growth & development*; D019346:Sodium Acetate / Q000494:pharmacology*; D013696:Temperature; D013997:Time Factors
D003470:Culture Media; D005520:Food Preservatives; D007773:Lactates; D019346:Sodium Acetate