Inactivation Kinetics of Pathogens during Thermal Processing in Acidified Broth and Tomato Purée (pH 4.5)

Area of Science:

• Food Microbiology
• Thermal Processing
• Food Safety

Background:

• Acidified foods, particularly tomato-based products, require validated thermal processes to ensure pathogen inactivation.
• Understanding the thermal inactivation kinetics of key foodborne pathogens is crucial for effective food safety.
• Accurate modeling of thermal inactivation is essential for process design and regulatory compliance.

Purpose of the Study:

• To determine the thermal inactivation kinetics of Shiga toxin-producing Escherichia coli (STEC), Listeria monocytogenes, and Salmonella enterica in acidified media.
• To compare log-linear and nonlinear (Weibull) models for describing pathogen inactivation.
• To provide data supporting thermal process validation for acidified tomato products.

Main Methods:

• Single strains and cocktails of STEC, L. monocytogenes, and S. enterica were heated in acidified tryptic soy broth (TSB) and tomato purée (pH 4.5).
• Inactivation curves were generated at various temperatures (52-58°C).
• Data were analyzed using log-linear and Weibull models to determine D-values and z-values.

Main Results:

• Both log-linear and Weibull models provided comparable D-values (time for 5-log reduction) across most trials, despite observed nonlinearity.
• Pathogen thermal resistance varied, with S. enterica showing lower D-values than L. monocytogenes and E. coli O157:H7 in tomato purée.
• Z-values (thermal resistance constants) for E. coli O157:H7 and S. enterica were similar and lower than for L. monocytogenes.

Conclusions:

• The Weibull model effectively describes thermal inactivation, and its parameters (t*, β) correlate well with D-values from the log-linear model.
• The findings support the use of thermal processing for acidified tomato products (pH ≤ 4.5) to control STEC, L. monocytogenes, and S. enterica.
• This research provides valuable data for small-scale processors needing to validate thermal lethality for acidified canned foods.