A Study on the Kinetic Behavior of Listeria monocytogenes in Ice Cream Stored Under Static and Dynamic Chilling and Freezing Conditions

Growth curves of Listeria monocytogenes in ice cream products A (a) and B (b) under different isothermal storage temperatures. Each point is a mean of 4 values. Vertical bars indicate the standard deviation.

Square root model for the effect of chilling temperature on the maximum specific growth rate (μ_max) of Listeria monocytogenes in 2 ice cream products (□: product A; ○: product B). Each point represents the mean of 2 replications from one experiment.

Predicted time-temperature conditions during the aging step that do not allow Listeria monocytogenes to exceed the level of 100 cfu/g at the end of the aging process, assuming a maximum potential contamination of 1 cfu/g for the ice cream mix prior to the aging step.

Comparison between the observed (points) and the predicted (lines) growth of Listeria monocytogenes in 2 ice cream products (□: product A; ○: product B) stored under periodically changing chilling conditions (a: 12h at 4°C, 6h at 8°C, and 12h at 12°C; b: 24h at 4°C, and 6h at 16°C). Each point represents one replication from the same experiment.

Survival of Listeria monocytogenes (open symbols: inoculation level of 10⁶ cfu/g; solid symbols: inoculation level of 10³ cfu/g) in ice cream (product A) stored under different isothermal freezing conditions. Each point is a mean of 4 values. Vertical bars indicate the standard deviation.

Comparison between observed (points) and predicted (lines) growth of Listeria monocytogenes in ice cream product A stored under 2 different dynamic chilling-freezing temperature profiles with random temperature fluctuations simulating temperature abuse during distribution and storage (a: profile A; b: profile B). Each point represents one replication from the same experiment.

Percent relative errors (%RE = [(n_observed−n_predicted)/ n_observed]×100, n in log cfu/g) for the comparison between the observed and predicted growth of L. monocytogenes in ice cream stored under dynamic temperature conditions (□ dynamic chilling conditions, ○: dynamic chilling-freezing conditions).