Combating heat-resistant microbes in milk plants

Combating heat-resistant microbes in milk plants

Work at South Dakota State University is aimed at developing ways to combat the heat-resistant microorganisms that challenge dairy industry.

FOR more than a century, milk has been heated to kill bacteria or pathogens that can affect consumer health and shorten the product's shelf life.

However, microbes known as thermoduric can survive pasteurization, according to South Dakota State University dairy science professor Sanjeev Anand. Now, he has begun developing ways to combat heat-resistant microorganisms — a major challenge for the world's dairy industry.

Some microbes protect themselves from heat by forming spores, which "makes them trickier to inactivate," Anand explained.

Additionally, these organisms attach and form colonies on the contact surfaces inside the milk processing equipment, according to Anand. As the colony expands, the layers form a biofilm that feeds and protects the organisms. The processing system environment essentially supports their growth, he reported.

Furthermore, many of these biofilm-embedded organisms cannot be inactivated through conventional cleaning methods.

Through his research, also supported by the Dairy Research Institute and the Midwest Dairy Food Research Center, Anand has found that milk products containing high microbe counts have flavor, texture and spoilage problems. Additionally, his work has revealed that some spore formers produce harmful toxins.

For nearly five years, Anand and his team of eight graduate and 10 undergraduate researchers worked on projects related to thermoduric bacteria and biofilms. Milk, cheese, milk powder and environmental samples were collected from 10 dairies in eastern South Dakota and three processing plants outside the state. The team then isolated the heat-resistant bacteria.

The information gathered is shared with producers and the dairy industry, Anand pointed out. "This helps establish a link with management practices to bring these counts down at a producer level and further control them during processing."

The isolates are being identified using techniques such as molecular typing and matrix-assisted laser desorption/ionization using time of flight, or MALDI-TOF. "We are approaching this very systematically using the latest technology," Anand explained.

The researchers are also investigating ways to either kill the microbes or make them susceptible to thermal treatment, which Anand described as "intervention prior to pasteurization or in combination with it."

Even in this preliminary stage of investigation, the team developed a method that, when combined with pasteurization, has been relatively successful in dealing with "vegetative cells of thermoduric spore formers to a large extent and spores to a lesser extent," Anand reported.

The process has been used with static or batch pasteurization and is being adapted to a continuous processing system.

If successful, Anand said, "we will have an integrated process at pilot scale to share with the industry."

The team also is targeting microbial biofilms, which form on joints, plate heat exchangers and filtration membranes within milk processing equipment.

Each organism gathered from the dairy facilities is being isolated and cultured to develop single and multi-species biofilms. "Under lab conditions, a biofilm can take anywhere from 12 to 48 hours to form," he explained.

This process helps the researchers determine under what conditions the biofilms form and, ultimately, "how we can change our cleaning system to remove them more efficiently and effectively," Anand said.

The biofilm-embedded microbes are studied not only in a static system but also in bioreactors that simulate the continuous flow of milk or whey. Anand said although the bioreactors are not pressurized like the automatic processing system, "this is closer to the real system."

Researchers are identifying which chemicals are effective on each species of organism and then will analyze the results to develop a better cleaning protocol to knock out these microbes.

When spore formers persist in an environment, they can also do irreversible damage to stainless steel contact surfaces within the milk processing equipment, which Anand explained can lead to corrosion in pre-heaters and spray dryers. Continued support from Dairy Research Institute will allow the research team to look at modifying the contact surfaces within the equipment to reduce the microbes' ability to colonize and form biofilms.

Through this multipronged approach at lowering thermoduric microbe levels, the South Dakota State researchers hope to improve the quality, safety and shelf life of dairy products.



Dairy producers have become increasingly aware of the economic consequences of suboptimal cow fertility and survival.

Using a range of modern breeds in both grass-based and high-input confinement production environments, recent research results illustrate greater fertility and survival for crossbred cows compared with pure Holstein cows, according to Dr. Bradley Heins, assistant professor in the University of Minnesota's department of animal science.

Crossbreeding, he said, allows a dairy producer "to exploit the favorable characteristics of 'alternative' breeds, remove the negative effects associated with inbreeding and capitalize on a phenomenon known as heterosis."

Heins cited research from Ireland concluding that of the dairy breeds used for crossbreeding — Normande, Montbeliarde and Norwegian Red — the Norwegian Red was most suited to seasonal grass-based production because of its fertility and survival advantages. A follow-up study confirmed a fertility advantage (a higher proportion pregnant after the breeding season) for the Norwegian Red x Holstein compared to the Holstein, Heins explained.

Studies conducted in Northern Ireland also found superior fertility performance with Jersey crossbred cows offered low- and moderate-concentrate diets.

In New Zealand, crossbred dairy cattle (primarily Jersey x Holstein) are achieving similar rates of genetic gain for profitability compared to the purebred populations but are creating additional gain derived from economic heterosis.

In the U.S., an analysis of data from California showed higher first-service conception rates for Scandinavian Red x Holstein and Montbeliarde x Holstein breeds than for Holsteins, and the crossbreds also had fewer days open and greater survival.

At The Pennsylvania State University, Brown Swiss x Holstein cows had 17 fewer days open than Holstein cows during the first lactation.

At the University of Minnesota, Jersey crossbred cows had higher first-service conception rates, fewer days open and a higher percentage that calved a third time compared with Holsteins.

"The literature clearly illustrates favorable animal performance benefits from crossbreeding ... within the context of both grass-based and high-input confinement production environments," Heins said.

Heins and his colleagues recently completed a study comparing crossbred cows sired by Montbeliarde bulls to Holstein cows. They evaluated cows during their first five lactations from March 2005 to February 2013.

They found that all crossbred cows had similar 305-day fat plus protein production compared to their Holstein herd mates during their first, second and third-and-greater lactations.

Heins noted that the results for production were reported on a 305-day projected basis, which does not necessarily reflect milk produced within a fixed interval of time because cows that died or left the herd were projected to 305 days.

The researchers found that the Montbeliarde x Holstein and Montbeliarde x Jersey/Holstein cows were superior to the Holsteins for fertility across the first five lactations.

"To put this into perspective, 23% more three-breed crossbred cows became pregnant after one service than Holsteins, and the crossbred cows were becoming pregnant one to two heat cycles sooner than the Holsteins (fewer days open)," he explained.

The researchers also recorded survival rates and found that all crossbred groups had a higher percentage of cows that calved a third, fourth and fifth time versus Holsteins. The Montbeliarde x Holstein had lower mortality rate than Holstein cows, at 5.1% versus 17.7%.

"The results indicate that Holstein cows were two times more likely to die on farm than Montbeliarde-sired crossbred cows during their lifetimes," Heins noted. "Mortality represents a significant loss of income for dairy producers because salvage value is lost, carcass disposal is costly, future production is lost and heifer replacement costs may not be recovered."

While the results showed similar production between crossbred and Holstein cows, Heins pointed out that the crossbred cows had advantages over Holsteins for fertility, survival and longevity.

"Advantages for these functional traits will compensate substantially for any potential loss of production of crossbreds compared to Holsteins," he said. 

Volume:86 Issue:19

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