Survival of Listeria monocytogenes in a Food Colorant Derived from Red Beets

¹ Department of Food Science and The Food Research Institute, University of Wisconsin at Madison, Madison 53706

Three commercial lots of the red beet colorant were inoculated to contain circa 10³ to 10⁷ Listeria monocytogenes strains California, V7, or Scott A per milliliter and stored for 56 d at 7°C. McBride listeria agar was used to determine numbers of survivors. Selected colonies thought to be L. monocytogenes were confirmed biochemically. When necessary, samples were tested by cold enrichment (up to 8 weeks). Samples of colorant initially containing 10³ to 10⁴ strain California/ml were always free of the pathogen after 56 d, and sometimes after 42 d. Samples with high initial numbers (10⁵ to 10⁶/ml) were not free of the pathogen after 8 wk at 7°C. Strains V7 and Scott A, regardless of size of initial population, always survived beyond 56 d. Before inoculation, all test samples of colorant were free of L. monocytogenes (direct plating or cold enrichment).

Key Words: Listeria monocytogenes • food colorant • red beets

Submitted on February 26, 1990
Accepted on June 11, 1990