A group of food scientists from Cornell University in New York have concluded that a standard quality test often used for raw organic milk is not sufficient for differentiating between specific groups of bacteria and should be updated. The research appeared in January in the Journal of Dairy Science (doi: 10.3168/jds.2023-24330).
Nicole Martin, PhD, senior author of the study and assistant research professor in dairy foods microbiology and the associate director of the Milk Quality Improvement Program in the Department of Food Science at the institution, says that the present test, known as the laboratory pasteurization count (LPC), searches for thermoduric bacteria, but doesn’t distinguish whether bacteria form spores or not.
She notes that when dairies deliver organic milk to processors, the milk is sometimes tested for thermoduric bacteria using LPC. Under current standards, if thermoduric bacterial counts are high, the milk can be downgraded or even rejected by the processor. “We saw firsthand the struggle that some dairy farmers had with controlling and troubleshooting the LPC in their raw milk, which selects for thermoduric bacteria, or bacteria that can survive temperatures considerably above their maximum growth temperature,” Dr. Martin tells Food Quality & Safety. “This can lead to loss of premiums and, ultimately, even loss of contracts if the LPC is not brought back into compliance.”
With that in mind, the researchers noted that the criteria for determining milk quality at processing plants is no longer valid and a new way for producers to address milk-production hygiene is necessary.
The researchers went into the study looking to answer a few questions about the LPC that they hear frequently from farmers and other stakeholders, including, “Can milk be frozen prior to LPC testing?” “What are the types of organisms making up the thermoduric population in organic raw milk?” and “Can a rapid identification method used primarily for mastitis organisms be used to identify thermoduric bacteria?”
“So, it’s not necessarily that the LPC is insufficient, but that the LPC alone can only give us so much information, and for farmers who are actively trying to reduce LPC, it may be beneficial to understand the types of bacteria leading to the elevated LPC,” Dr. Martin adds. “This would also for more targeted troubleshooting efforts.”
The research showed that there are two different groups of bacteria making up the thermoduric population in organic raw milk—sporeformers and non-sporeformers—and an individual milk sample with a high LPC may have one or the other, or both, of these types. “Once we know what type of bacteria is driving the elevated LPC, it then allows for more targeted troubleshooting since these groups of bacteria are likely to originate from different sources on the farm,” she says. “We’re giving organic farmers the knowledge they need to make high-quality raw milk and for it to be economically viable; it will make a better dairy product in the end.”
The investigators concluded that, when troubleshooting elevated LPC, it is beneficial to know what the predominant type of thermoduric bacteria are that are contributing to the LPC. “Overall, our research shows that organic raw milk quality is very good, but some producers occasionally deal with high bacteria levels, and often it can take a lot of time and resources to resolve those issues,” Dr. Martin says. “So, when a farmer is dealing with this issue, it is a big problem for them.”
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