Shredded cabbage was inoculated with Listeria monocytogenes Scott A cells and stored in normal air or a modified (70% carbon dioxide and 30% nitrogen) atmosphere at 5 and 25°C. Under the normal atmosphere at 25°C, colony counts increased by 2 logs within 2 d of storage but then decreased to undetectable levels within 6 d of storage. In the modified atmosphere at 25°C, numbers also decreased to undetectable levels within 6 d, but with a less marked initial increase and a decline that was more rapid than in the unmodified atmosphere. In the cold (5°C), the counts increased gradually, but only by about 1 log, in both atmospheres. In the normal atmosphere at 5°C, however, colony counts decreased sharply after 13 d of storage. Reductions in colony counts coincided with decreases in cabbage pH and development of spoilage. The increased level of carbon dioxide was ineffective in controlling L. monocytogenes at 5°C. At 25°C cabbage spoilage was rapid and colony counts declined under both atmospheres of storage.
1Denver District Laboratory.
2Division of Microbiology, Washington. DC.
3Colorado State University