Tracking spore-forming bacterial contaminants in fluid milk-processing systems

Area of Science:

• Food Microbiology
• Dairy Science
• Molecular Biology

Background:

• Psychrotolerant spore-forming bacteria, including Bacillus and Paenibacillus species, are a major challenge for extending the shelf life of pasteurized fluid milk.
• Current shelf life limitations for high-temperature, short-time (HTST) pasteurized milk are often around 14 days due to microbial spoilage.

Purpose of the Study:

• To characterize spoilage bacteria in raw milk supplies using a DNA sequence-based subtyping method.
• To assess the transmission of these spoilage organisms from raw milk into pasteurized products within two processing plants.

Main Methods:

• A recently developed rpoB DNA sequence-based subtyping method was employed.
• Samples of raw milk (n=39) and pasteurized products (n=11) were collected across the processing continuum.
• Bacterial isolates were enumerated after cold storage (6°C for up to 16 days).

Main Results:

• A total of 88 bacterial isolates were characterized, yielding 31 distinct rpoB allelic types of Bacillus and Paenibacillus species.
• Five specific bacterial allelic types were detected in both raw milk sources and finished pasteurized products.
• The presence of identical subtypes in both raw and finished milk indicates contamination originating from the raw milk supply.

Conclusions:

• The raw milk supply is a significant source of psychrotolerant spore-forming bacteria that cause spoilage in pasteurized milk.
• Eliminating these specific bacterial contaminants from milk-processing systems is essential for extending the shelf life of HTST pasteurized fluid milk.
• Further research into controlling spore-forming bacteria in raw milk is needed to improve dairy product longevity.