Gram-negative postpasteurization contamination patterns of single-serve fluid milk produced in 4 different processing...

Area of Science:

• Food Microbiology
• Dairy Science
• Food Safety

Background:

• Historic data indicates single-serve milk has higher bacterial counts and lower sensory scores at 14 days postprocessing compared to half-gallon containers.
• Postpasteurization contamination with gram-negative bacteria is a suspected cause of increased spoilage in single-serve milk.

Purpose of the Study:

• To comprehensively assess the microbial quality and shelf life of single-serve high temperature, short time (HTST) fluid milk.
• To identify the sources of gram-negative contamination in single-serve milk production.

Main Methods:

• Analysis of 265 commingled single-serve HTST fluid milk samples from four commercial facilities over two visits.
• Microbial quality assessment, including gram-negative bacteria spoilage frequency and bacterial counts.
• In-facility surveys and ATP swab tests to identify contamination sources, focusing on carton forming mandrels.

Main Results:

• Gram-negative spoilage frequency ranged from 14% to 79% across facilities, with significant variations between visits, facilities, milk types, and filler lanes.
• Milk with gram-negative contamination exhibited higher bacterial counts and lower sensory scores on days 7 and 14.
• Bacterial genera like Pseudomonas and Bacillus were frequently isolated from both milk samples and carton forming mandrels.

Conclusions:

• The unhygienic design of single-serve fillers is a likely root cause of gram-negative contamination.
• Despite interventions to improve cleaning of carton forming mandrels, gram-negative spoilage frequency was not significantly reduced.
• Further investigation into filler design and sanitation protocols is crucial to improve single-serve milk quality.