Growth and thermal inactivation of Listeria monocytogenes in cabbage and cabbage juice

Abstract

Studies were done to determine the interacting effects of pH, NaCl, temperature, and time on growth, survival, and death of two strains of Listeria monocytogenes. Viable population of the organism steadily declined in heat-sterilized cabbage stored at 5 °C for 42 days. In contrast, the organism grew on raw cabbage during the first 25 days of a 64-day storage period at 5 °C. Growth was observed in heat-sterilized unclarified cabbage juice containing ≤5% NaCl and tryptic phosphate broth containing ≤10% NaCl. Rates of thermal inactivation increased as pH of clarified cabbage juice heating medium was decreased from 5.6 to 4.0. At 58 °C (pH 5.6), 4 × 106 cells/mL were reduced to undetectable levels within 10 min. Thermal inactivation rates in clarified cabbage juice (pH 5.6) were not significantly influenced by the presence of up to 2% NaCl; however, heat-stressed cells had increased sensitivity to NaCl in tryptic soy agar recovery medium. Cold enrichment of heat-stressed cells at 5 °C for 21 days enhanced resuscitation. Results indicate that L. monocytogenes can proliferate on refrigerated (5 °C) raw cabbage which, in turn, may represent a hazard to health of the consumer. Heat pasteurization treatments normally given to cabbage juice or sauerkraut would be expected to kill any L. monocytogenes cells which may be present.