Food sanitization is a crucial aspect of the agri-food chain to ensure the safety and quality of food products, extending their shelf life and reducing waste. Typically, most operations in the food industry use heat as an energy source for processing and sanitizing food. While thermal processes are effective in microbial and enzymatic inactivation, they can significantly impact the nutritional and sensory quality of foods.

To minimize the negative effects of temperature by reducing the contact time between food and heat during processing, many studies have evaluated the effectiveness of pre-treatments, such as ultrasound, pulsed electric fields, high pressure, and ethanol. However, these technologies also present notable challenges. The energy dissipated by ultrasound can damage cell structure, decreasing food rigidity and its sensory acceptance, while high pressure can induce physical alterations that affect both the appearance and quality of foods. Other non-thermal technologies, such as chlorinated water washing, often leave residues and are not suitable for dry foods, which do not respond well to liquids. This is why, in recent years, cold plasma has emerged as an innovative and eco-friendly technology for enhancing food safety.

Plasma was discovered by William Crookes in 1879. While studying electrical charges in gas, Crookes observed a light produced by what he called “radiant matter”. It wasn’t until 1928, however, that Irving Langmuir officially named it plasma. Langmuir went on to win the Nobel Prize for his studies on the effects of plasma on materials it came into contact with, particularly the containers in which it was produced.

Plasma consists of a gas that can be either partially or fully ionized, and it exists in two types: thermal plasma and non-thermal (or cold) plasma. Thermal plasma is a state of matter reached when a system receives a large amount of energy, putting all particles in energetic equilibrium. In contrast, non-thermal plasma is generated at atmospheric pressure or under vacuum, with particles that are not in equilibrium. In this case, it is referred to as ionized plasma, meaning that a certain percentage of electrons has been removed from its atoms.

Cold plasma, despite its name, has a temperature of 25 degrees Celsius and a pressure of 1 atmosphere, so it does not require refrigeration. It is commonly generated by the interaction between an electric field and air, creating a mixture of electrons and ions. This mixture is further excited by the electric field, which promotes collisions with air atoms and molecules, producing a large number of new charged particles. Cold plasma generated in this way exhibits antimicrobial characteristics and effects, sparking researchers’ interest in applying this new technology in the food sector to prevent the proliferation of bacteria, microbes, and pathogens harmful to the products we consume.

Many studies on cold plasma focus on bacterial species such as Salmonella, Escherichia coli, and Listeria monocytogenes, some of the most common foodborne pathogens responsible for gastroenteritis, diarrhea, and food contamination. These conditions lead to tens or even hundreds of thousands of deaths worldwide, particularly among children. Escherichia coli, for example, causes approximately 760,000 cases of severe diarrhea fatalities each year among children under the age of 5.

Given its characteristics, plasma is also used as a pretreatment for various processes, thereby expanding its range of applications in the food sector. It can, for instance, reduce the time required for drying, improve food extraction and cooking, and transform saturated fats into unsaturated ones without producing unwanted chemical species. Plasma can also be used to deposit a film onto a base material, allowing for the slow release of a substance, such as a fungicide.

Within this technological framework, the Physan project of Spoke 2 aims to use plasma to reduce fungal contamination and mycotoxins in cereals and legumes, selecting suitable bacterial strains as protective agents and assessing the effectiveness of treatments. Romolo Laurita, a researcher at the Department of Industrial Engineering at the University of Bologna and one of the professors overseeing the PHYSAN research activities, explains: 

“For the PHYSAN project, we built a prototype that generates cold plasma. It’s a box the size of an A4 sheet, about 2-3 cm high. The food to be decontaminated is placed inside the box, and the upper wall generates a plasma discharge. This discharge is created through a high-voltage generator and electronic components that ionize the air, producing reactive species, including ozone, which diffuses within the box to sanitize the food”.

The prototype Laurita mentioned is at an advanced development stage; however, its practical application faces specific challenges related to the structure of the food being decontaminated. “One drawback,” Dr. Laurita continues, “is that it’s a surface approach that does not penetrate the food, so it depends on the structure of the food. For example, if the food is whole, it will be sterile inside; if it’s sliced, such as in ready-to-eat products, each part exposed to air needs to be sanitized. Additionally, one carrot can differ from another and may experience various types of contamination depending on when it is harvested, processed, and delivered. Many tests are therefore needed to find the optimal configuration that can act across a broader spectrum.”

Scalability is certainly one of the prototype’s limitations. For a box the size of an A4 sheet, a generator is required, and to increase capacity, multiple generators are necessary, which raises costs. Finally, although cold plasma does not affect the organoleptic properties or nutritional characteristics of fruits and vegetables, researchers still aim to carefully analyze any possible unintended effects of plasma use on food composition.

Projects like Physan, which experiment with new ways to apply plasma, are paving the way for concrete innovations that could radically transform the agri-food sector, reducing waste and improving public health on a large scale. In a context where sustainability and food safety are global priorities, research into this technology represents a strategic investment, not only for the industry.