U.S – A study by Cornell University researchers has revealed that improper cleaning of equipment in the microfiltration process can introduce pasteurization-resistant bacteria into fluid milk, potentially compromising its safety.

Microfiltration is an emerging technology designed to prolong the shelf life of milk by employing semipermeable membranes to exclude undesirable microbes.

It offers an alternative to high-temperature ultra-pasteurization for extending milk’s shelf life. Unlike ultra-pasteurization, which can impart a “cooked” flavor to milk, high-temperature, short-time (HTST) pasteurization is favored in the United States for preserving the natural taste of milk.

Microfiltration achieves microbial reduction in raw milk by utilizing membrane pores measuring 0.8–1.2 microns.

This process demands less energy compared to pasteurization and preserves milk’s flavor. By eliminating bacteria, microfiltration can extend the refrigerated shelf life of fluid milk products from 14–21 days to an impressive 60 days.

This technology, already in use in Europe, is poised for adoption in the U.S.

However, the Cornell study emphasizes the critical need for thorough cleaning of equipment involved in handling raw milk well before the pasteurization step.

If equipment is not cleaned adequately and in a timely manner, microfiltration may allow very small, pasteurization-resistant microbacteria to enter fluid milk.

The research conducted by Cornell involved observing whole milk and skim milk samples that underwent both microfiltration and pasteurization processes.

These samples were subsequently refrigerated at temperatures of 3 °C, 6.5 °C, and 10 °C for a period of 63 days.

The study found that the amount of bacteria in the milk samples increased with higher refrigeration temperatures, with no significant variation based on fat content.

Of particular concern was the presence of microbacteria, which managed to penetrate microfilter membranes, survive HTST pasteurization, and thrive at refrigeration temperatures.

This research underscores the importance of rigorous cleaning protocols for equipment used in the microfiltration process, ultimately ensuring the safety and quality of extended-shelf-life milk products.

“Fluid milk processors often rely on the pasteurization process to apply the final kill-step for organisms,” Martin said, “but we’re showing that to achieve a longer shelf-life with this newer technology, processors should thoroughly clean the intake equipment for raw milk long before they pasteurize.

In other words, they should do everything they can to remove these microbes prior to processing,” said Nicole H. Martin, Associate Director of Cornell’s Milk Quality Improvement Program.

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