Aerobio Growth of Listeria monocytogenes on Beef Lean and Fatty Tissue: Equations Describing the Effects of Temperature and pH

Abstract

The aerobio growth rate and the duration of the lag period were determined for Listeria monocytogenes strain Murray B growing on ground beef lean and on pieces of fatty tissue. The organism grew at 0°C on lean tissue at pH ≥ 6 and on fatty tissue. It failed to grow at 0°C on lean at pH 5.6 but did grow at 2.5°C. The effect of temperature, between 0 and 30°C, on the growth rate on fatty tissue can be described by a modified Arrhenius equation Ln (gen/h) = −205.73 + 1.2939 × 10⁵/K −2.0298 × 10⁷/K², where K = °Kelvin. This equation accounted for 99.7% of the variance. The combined effect of temperature and pH on the growth rate on beef lean was described by Ln (gen/h) = − 232.64 + 1.4041 × 10⁵/K - 2.1908 × 10⁷K² + 1.1586 × 10²/pH - 4.0952 × 10^2/pH² (variance accounted for 99.5%). For lean at about pH 5.5–5.6, this equation applied between about 2.5 and 35°C; for lean of pH 6–7, it applied between about 0 and 35°C. Though the lag period increased with decrease in temperature and pH, measured lag times were more variable than generation times, and the goodness of fit of modified Arrhenius equations to lag times was relatively poor (variance accounted for 83–92%).