Heat resistance of Listeria monocytogenes

Area of Science:

• Food microbiology
• Dairy science
• Food safety

Background:

• Raw milk consumption poses risks due to potential pathogen contamination.
• Listeria monocytogenes is a significant foodborne pathogen of concern in dairy products.
• Thermal processing is a common method to reduce microbial load in milk.

Purpose of the Study:

• To investigate the survival of Listeria monocytogenes in raw milk after heat treatment.
• To determine the efficacy of different temperatures in eliminating Listeria monocytogenes.
• To assess the necessity of cold enrichment for detecting thermally injured Listeria monocytogenes.

Main Methods:

• Raw milk was inoculated with Listeria monocytogenes.
• Milk samples were subjected to heat treatments ranging from 69°C to 73°C.
• Post-heating, samples were stored under refrigeration.
• Bacterial recovery was performed after variable periods of cold storage.
• Cold enrichment techniques were employed to detect surviving organisms.

Main Results:

• Listeria monocytogenes was recovered from 46.6% of heat-treated milk samples.
• No Listeria monocytogenes were detected in samples heated at 73°C.
• Survival of Listeria monocytogenes was observed after thermal treatments below 73°C.
• Thermally injured Listeria monocytogenes required cold enrichment for recovery.

Conclusions:

• A small population of Listeria monocytogenes can survive pasteurization temperatures.
• Heat treatment at 73°C effectively eliminated Listeria monocytogenes under the tested conditions.
• Cold enrichment is essential for the detection and recovery of sublethally injured Listeria monocytogenes in milk.
• These findings highlight the importance of process control and sensitive detection methods in ensuring milk safety.