Dealing with thermoduric microbes in the dairy industry

While pasteurisation may have revolutionised the food industry, certain microbes can survive pasteurisation. In the dairy processing industry, these heat-resistant - or thermoduric - microbes can turn milk sour and leave cheese soft and crumbly. Some even thrive in high temperatures.

Sanjeev Anand, a South Dakota State University dairy science professor, is developing ways to combat these heat-resistant microorganisms.

For nearly five years, Anand and a team of 18 researchers have worked on projects related to thermoduric bacteria and biofilms. They collected milk, cheese, milk powder and environmental samples from 10 dairies in South Dakota and three processing plants throughout the US, and then isolated the heat-resistant bacteria.

The isolates are identified using techniques such as molecular typing and MALDI-TOF (matrix-assisted laser desorption/ionisation using time of flight). The researchers are investigating ways to either kill the microbes or make them susceptible to thermal treatment, which Anand describes as “intervention prior to pasteurisation or in combination with it”.

The team has developed a method which, when combined with pasteurisation, has been relatively successful in dealing with vegetative cells of thermoduric sporeformers, with some success dealing with spores. The process has been used with a static or batch pasteurisation and is being adapted to a continuous processing system.

In addition, the team has also targeted microbial biofilms, which form on joints, plate heat exchangers and filtration membranes within the milk processing equipment. Each organism gathered from the dairy facilities is isolated and cultured to develop single- and multi-species biofilms.

This process helps the researchers determine under what conditions the biofilms form and, ultimately, how cleaning systems can be changed to remove biofilms more efficiently and effectively.

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. “This is closer to the real system,” said Anand.

The researchers are working to identify which chemicals are most effective on each species of organism and will analyse these results to develop a better cleaning protocol to knock out these microbes.

Anand’s work is supported by the Dairy Research Institute and the Midwest Dairy Food Research Center