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Cold Atmospheric Plasma (CAP) sterilization of powdered products: optimization and validation at alimentary and pharmaceutical levels

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Making sure ‘sleeping’ spores do not wake

Many products intended for human consumption are sold in powder form, but inherent dormant microbial spores can wreak havoc upon rehydration. EU research is paving the way to eco-friendly and safe treatment of powdered products.

Industrial Technologies icon Industrial Technologies
Food and Natural Resources icon Food and Natural Resources

Baby foods, spices, vitamin and protein complexes, and insect- or algae-based foods are among the many powdered products that exploit powder’s stability, long shelf-life and simplified transportation. However, effectively inactivating inherent microbial spores with conventional heat treatments is challenging, and subsequent air cooling poses additional risk of recontamination. CAP SAliPharm, the first Marie Skłodowska-Curie Individual Fellowship, MSCA-IF ever awarded to a University of Applied Sciences, set out to evaluate the use of a novel plasma technology to safely prepare powders for packaging.

From primordial soup to our tables

Plasma is a fourth state of matter, a gas so hot that the vigorous collisions among atoms and molecules cause most or all electrons to be ripped free. This hot ionised gas is the stuff of which stars are made. In the laboratory, cold atmospheric plasmas, CAPs are generated by free electrons in an electric field rather than extremely high temperatures. These partially ionised gases at room temperature and standard atmospheric pressure consist of a mix of electrons, ions, excited atoms and molecules, reactive species, UV radiation and heat. The content and environmental conditions make CAPs particularly amenable to practical applications. CAP-SAliPharm set out to harness the reactive species and UV light to reduce the viability of microbes in powders. “The non-thermal, low energy processing achieved with CAP technology, relative to conventional dry- or wet-heat processing or high-energy radiation, should preserve desired food properties better. No chemicals or long living toxic compounds are used or produced. Finally, if green electric energy generates the plasma, the environmental footprint of sterilisation is minimised,” explains CAP-SAliPharm coordinator Michael Beyrer of the University of Applied Sciences and Arts of Western Switzerland (HES SO).

Overcoming powders’ challenges

CAP technology has been used as an antimicrobial surface treatment in industry but never in the context of products intended for human consumption. Powder generally decreases the rate and efficacy of CAP spore inactivation relative to other matrices. CAP-SAliPharm had two key objectives: to characterise and quantify the factors affecting inactivation efficacy and to evaluate potential side effects. The team assessed bacterial spores on a number of organic and inorganic particles with various features. Fellow Maria Consuelo Pina-Pérez summarises: “We found that the inactivation effects of CAP on dormant spores are predictable and scalable, primarily determined by the discharge power and the process time. A very low discharge power density in the range of a few mW/cm2 and a process time of a few minutes produced decades of inactivation.” Importantly, achieving such impressive outcomes with such low applied energy should reduce potential side effects.

Building on the past, working toward the future

The CAP-SAliPharm team has been assessing reference strains of pathogenic microorganisms in food powders for some time, including those found in an industrial environment in addition to those inherent to the preparations. The current collaboration with Nestlé has put increasingly stringent regulations in the spotlight. Beyrer summarises: “The project integrates preliminary and follow-up work and promotes pan-European communication among the scientific community. This is an equally important outcome, expediting commercialisation of an emerging technology.” Dissemination campaigns have met with tremendous enthusiasm and the team is preparing to scale the technology, build partnerships and head to market with benefits for consumers and industry alike.


CAP-SAliPharm, cold atmospheric plasma (CAP), powder, spores, inactivation, plasma, food, microbial, sterilisation

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