Abnormal Freezing of Milk Caused by Ice-Nucleating Bacteria

Area of Science:

• Microbiology
• Food Science
• Dairy Science

Background:

• Raw milk can contain microorganisms that influence its physical properties.
• Ice nucleation is a critical factor in food processing and storage.

Purpose of the Study:

• To identify ice nucleating bacteria in raw producer bulk milk.
• To investigate the role of these bacteria in milk freezing behavior.

Main Methods:

• Isolation and identification of bacteria from raw milk.
• Cryoscopic testing of milk samples to assess freezing points.
• Assessing the impact of bacterial cultures on milk's ice nucleating activity.

Main Results:

• Gram-negative rods, predominantly Pseudomonas fluorescens, were identified as ice nucleating bacteria.
• Milk samples containing these bacteria exhibited premature freezing during supercooling.
• Cultured bacterial cells transferred to normal milk samples induced ice nucleation.

Conclusions:

• Pseudomonas fluorescens in raw milk possesses ice nucleating capabilities.
• These bacteria can significantly affect the freezing properties of milk.
• Understanding bacterial ice nucleation is crucial for dairy processing and quality control.