Quantifying growth of cold-adapted Listeria monocytogenes and Listeria innocua on fresh spinach leaves at refrigeration temperatures

The Baranyi model was used to obtain the initial cell concentration, yo, lag time, tlag, maximum cell concentration, ymax, and maximum growth rate, μmax, using data collected on the growth of cold-adapted (CA) Listeria monocytogenes and Listeria innocua on fresh spinach leaves under refrigeration temperatures (3, 5, and 8 °C). For L. monocytogenes, a dynamic model was validated for ymax, tlag, and μmax. Although L. monocytogenes grew on the leaves at all refrigeration temperatures, L. innocua did not show growth at 3 °C. At 5 and 8 °C, the growth parameters (tlag and ymax) for L. monocytogenes and L. innocua were significantly different (P < .05). Therefore, CA L. innocua is not a suitable surrogate for CA L. monocytogenes in growth studies. Total aerobic mesophilic and psychrotrophic microorganisms restricted growth of L. monocytogenes at 3-8 °C on the leaves.