Identification of Listeria innocua as a biological indicator for inactivation of L. monocytogenes by some meat processing treatments

Abstract

Four strains of Listeria monocytogenes and two strains of L. innocua were studied for their response to heat, gamma radiation, lactic acid and sodium nitrite treatments generally used in the meat industry. Listeria spp., when heated in 10% meat homogenate at 75 °C, showed a phenomenal tailing effect with a thermal death time of 1 min. The D10 value (dose required for 10% survival) of Listeria spp. to gamma radiation in phosphate buffer at -40 °C was observed to be higher (0.3 kGy) than at 0 °C (0.15 kGy), whereas the protection offered by 10% meat homogenate did not vary with change in irradiation temperature (D10 = 0.5 kGy at 0 ° and -40 °C). While 1.25 g/L lactic acid in brain heart infusion (BHI) or meat homogenate was bacteriostatic, a higher concentration (> 1.25 g/L) was bactericidal to both Listeria spp. The combined effect of 1.25 g/L lactic acid and 10 g/L NaCl was also bactericidal. Growth inhibition of Listeria spp. by either lactic acid or NaNO2 at low pH was also demonstrated. The overall response of both Listeria spp. to these processing treatments were comparable suggesting possible use of L. innocuua in lieu of L. monocytogene for the safe evaluation of processes used in the meat industry to control potentially hazardous L. monocytogenes. © 1996 Academic Press Limited.