Assessing Raw Milk Quality: Understanding Laboratory Pasteurization Count (LPC)
Laboratory pasteurization count (LPC) serves as a crucial tool for evaluating the quality of raw milk. Some dairy producers utilize LPC data to determine raw milk quality premiums for farmers and to troubleshoot bacterial contamination problems. LPC primarily identifies thermoduric bacteria, which possess the ability to survive pasteurization. However, distinguishing between sporeformers and non-sporeformers based solely on LPC levels remains a challenge.
A recent study conducted by researchers at Cornell University aimed to investigate whether LPC levels could indicate the presence of specific types of bacteria in raw milk. The researchers collected 94 organic raw milk samples from various locations across the US, analyzed them using LPC, and characterized the bacterial isolates. The study revealed a range of LPC concentrations, from undetectable to 4.07 log10 cfu/mL. The thermoduric bacteria isolated from the samples were classified into three groups: gram-positive sporeformers (52%), gram-positive non-sporeformers (44%), and gram-negative bacteria (2.4%).
Among the samples tested, the majority (66) exhibited LPC levels ≤100 cfu/mL, six samples had LPC levels between 100 and 200 cfu/mL, and ten samples had LPC levels ≥200 cfu/mL. Interestingly, an inverse relationship was observed between the proportion of gram-positive sporeformers and LPC concentration. Samples with higher LPC levels tended to have lower proportions of gram-positive sporeformers, although this trend was not deemed statistically significant by the researchers.
The researchers concluded that LPC levels alone do not provide sufficient information about the composition of thermoduric bacteria in raw milk. Further characterization is necessary to identify the bacterial factors contributing to elevated LPC levels. Leveraging a microbial identification tool known as MALDI-TOF MS, the researchers compared the method to 16S rDNA PCR and sequencing. While MALDI-TOF MS showed agreement with 16S at the genus level for 66.6% of isolates, 24.2% and 9.2% could not be accurately identified or were mischaracterized using MALDI-TOF, indicating the need for method optimization.
The study underscores the importance of developing rapid and accessible bacterial testing methods for the dairy industry to enhance milk quality troubleshooting efforts. By advancing characterization techniques, producers, cooperatives, and processors can better understand the microbial composition of raw milk and improve outcomes for all stakeholders involved in dairy production. This research provides valuable insights into the complexity of thermoduric bacteria and highlights the limitations of LPC as a standalone indicator of raw milk quality.
Source:
Troubleshooting high laboratory pasteurization counts in organic raw milk requires characterization of dominant thermoduric bacteria, which includes non-sporeformers as well as sporeformers
Authors: Lee, T. R., et al
Published: Journal of Dairy Science, 20 January 2024
DOI: 10.3168/jds.2023-24330
Read More: [High-Quality Raw Milk Needs Rapid and Accessible Bacterial Testing Methods](https://www.dairyreporter.com/Article/2024/02/12/high-quality-raw-milk-needs-rapid-and-accessible-bacterial-testing-methods?utm_source=RSS_Feed&utm_medium=RSS&utm_campaign=RSS)