The lethal effect of carrot on Listeria species

When shredded or sliced carrots were inoculated with Listeria monocytogenes the number of viable listerias decreased rapidly. On carrot slices stored at 8 degrees C there was a decrease after 3d followed by an increase, after 7d, to numbers similar to those present initially. The numbers of spoilage micro-organisms increased throughout storage at 8 degrees C. Carrots macerated in a Stomacher Lab Blender also showed an antilisterial activity which resulted in a decrease in number of viable bacteria and in sublethal damage. The effect was shown by five carrot cultivars and acted on nine strains of L. monocytogenes and single strains of L. innocua, L. ivanovii, L. seeligeri, L. melshimeri. This antilisterial effect was heat-labile, was inactivated after a few hours at 4 degrees C or at 30 degrees C and was active over the pH range 5.8 to 7.0. Maceration of carrots in an Atomix blender for 1 min or in liquid nitrogen destroyed the antilisterial activity.