Purpose: The objective of the research was to evaluate the performance of Combase model (for E. coli O157:H7) and Ratkowsky square-root model recommended by Huang for the prediction of the growth of STECs in ground beef (Huang model).
Methods: Irradiated ground beef (fat, 73/27; and lean, 93/7) was inoculated with ca. 2 CFU/g of five-strain cocktails of O157:H7, O26, O45, O103, O104, O111, O121, O145, and six-serovar STEC cocktails from USDA-ARS and ATCC, respectively. Inoculated ground beef was packaged in vacuum bags, placed in programmable water baths to follow time-varying temperature profiles (sinusoidal; low or high temperature profiles) for a total of 300h and 25h, respectively. Growth data were collected and fitted into the models described by Huang and Combase. Model performance indicators (Root mean squared error, RMSE; bias factor, BF; and accuracy factor, AF) were calculated to evaluate the performance of these models.
Results: The Huang model underestimated the growth of all STECs for both temperature profiles; the average RMSE for fat and lean meat were 1.87 and 2.14 at low temperature, and 2.39 and 2.42 at high temperature profiles. Combase model over-predicted the growth of all STECs with a mean RMSE of 1.44 and 1.60 log CFU/g for fat and lean ground beef, respectively. Besides, Combase model cannot predict the growth of E. coli O157:H7 at temperatures below 10°C where growth of STEC can occur.
Significance: None of the two models precisely predicted the growth of STECs in ground beef. However, Combase could be a conservative option given the limited availability of predictive models for STECs.