New method uses electric shocks to kill bacteria

Harmful bacteria are inactivated by means of electroporation while maintaining product quality during the processing of whey proteins

A team from the University of Natural Resources and Life Sciences (BOKU) in Vienna, have identified conditions for inactivating Listeria, and other germs, while maintaining product quality during the processing of whey proteins. The new method, known as electroporation, destroys the harmful bacteria without damaging nutrients.

The researchers, in collaboration with an international food company, found that low temperatures and an acidic environment create the ideal conditions for applying an effective method of inactivating harmful bacteria in the processing of whey protein solutions without destroying valuable nutrients.

The conditions identified by the BOKU researchers will pave the way for the preservation of whey-protein solutions without significant loss of nutrients.

Electric weapon

Removing bacterial contamination from foodstuff is a challenge. Several methods are available, but getting the right “dosage” is a balancing act.

Procedures for ridding a product of germs also kill off valuable nutrients; but the flip side is that less aggressive processes do not remove the bacteria sufficiently.

The new method relies on what is known as pulsed electric fields (PEF), which destroy bacterial cell membranes but also use considerably lower temperatures than those applied in conventional thermal preservation.

Until now, this process has mainly been used with fruit juices and other fluid foodstuff.

Cool and acidic balance

Commenting on the findings, Henry Jäger, Deputy Head of the BOKU’s Institute of Food Technology, said: “Temperatures of 20°C or so and an acidic environment with a pH value of about 4 are ideal conditions for electroporating bacteria in protein solutions like the whey protein we tested.”

In this context, “ideal” means that sufficient bacteria are inactivated while also preserving valuable ingredients to the greatest possible extent.

This extremely precise analysis of process conditions and their implementation was made possible by the comprehensive range of equipment supplied by Vienna-based EQ BOKU, a partner of the University of Natural Resources and Life Sciences.

The study compared two different concentrations of whey proteins (2% and 10%). A Listeria strain that is harmless to humans was then added to these solutions and the degree of inactivation resulting from pulsed electric fields of different intensities was compared. A temperature of between 20°C and 40°C, and a pH value of 4 or 7, was selected.

After electroporation, the residual level of sensitive nutrients, such as vitamins and immunoglobulins, and the Listeria concentration were measured.

“Temperature plays a decisive part in this process,” Jäger explained, adding that the energy produced by the pulsed electric field causes the medium to warm quickly, which damages many valuable proteins. “This effect increases in line with the strength and duration of the electric field, which in turn kills off the bacteria more efficiently. So, it’s all about finding the right balance.”

The research team showed that a low starting temperature of about 20°C and a pH value of 4 represents the ideal equilibrium, allowing for greater intensity of the electric pulses and, in turn, effective inactivation of the Listeria.

The study will make an important contribution to the development of more efficient and less damaging methods of removing germs from sensitive products, as well as enhancing overall food safety.

Reference

Pulsed electric field preservation of liquid whey protein formulations – Influence of process parameters, pH, and protein content on the inactivation of Listeria innocua and the retention of bioactive ingredients. F. Schottroff, M. Gratz, A. Krottenthaler, N. B. Johnson, M. F. Bédard, H. Jaeger. 2019. Journal of Food Engineering, Volume 243, pages 142-152. https://doi.org/10.1016/j.jfoodeng.2018.09.003

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