Plasma

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Cold Plasma Technology


General Information

Overview

Plasma technology is used already in industry to treat glass, electronic, textiles, paper and other products at commercial scale. (Niemira 2014). There are two typical commercial applications: Modification of the surface energy to improve adhesion between different polymers or between an aluminum coating and a polymeric substrate; and the modification of the surface chemistry to improve polymer functionality (Muredzi 2012).

The technical aspects of cold plasma largely unfamiliar to food producers. (Niemira 2014). It has a high potential for fragile surface foods processing as fruits and vegetables. (Muredzi 2012). Plasma technology is diverse and flexible with new systems continuously being built. (Niemira 2014).


Advantages

  • Effect of multiple antimicrobial mechanisms simultaneously.
  • Low pressure and low temperature processing parameters.
  • Scalable technology (from pilot to industry).
  • Recognized as more cost effective than chemical sterilization.

(Niemira 2014)


Disadvantages

  • Cost of the feed gas + electricity use are critical.
  • Critical evaluation of the interaction between the food and the different species formed in the plasma is needed. (Niemira 2014)
  • Technology in Infancy stage, chemical processes not fully understood. (Muredzi 2012)


Base

  • Plasma is comparable to an ionized gas consisting of neutral molecules, electrons, and positive and negative ions. When a gas is given sufficient energy, its intramolecular and intra-atomic structures break down liberating free electrons and ions. When the separated particles of the ionized gas recombine, the applied energy is realized as visible light, ultra violet light and the creation of new chemical species.
  • The gas´s ionization voltage is determined by the distance between the electrodes, the shape of the electrodes and the gas pressure.
  • For the generation of cold plasma there is need of an arch discharge, enabled by an ionizing voltage differential created between two electrodes. A stream of gas expands and cools until it discharges upwards, as with the gliding arch.
  • The chemical composition of the feed gas is critical to the resulting contact behavior with food.

(Niemira 2014)


Description of techniques

  • The driving force for the generation of plasma is typically electricity, but it is also possible to use microwaves or lasers.
  • There are three different categories of plasma techniques in food processing depend on where the food is with respect to the cold plasma being generated. The first category is the “Remote treatment” at some significant distance from the point of plasma generation, it has a flexible and simple design, but there is a recombination of plasma species among themselves before they reach the food leading to a less effective exposure; the second category is “Direct treatment” in which the food is relatively close to the point of generation with the full effect of plasma but with the risk of electricity conduction; the last category is the “electrode contact” in which the product is within the plasma generating field itself, with a maximum exposure but potential discharge possibilities and the limitation of the space between the electrons.
  • Air can be used as feed gas, helium is easy to ionize and the other noble gas are commonly used. Combinations of different gases can also be used as feed gas.
  • Alternative techniques for cold plasma generation are microwaves and radio frequency: Micro wave pumped system: Use microwaves in the treatment chamber to enable the ionization. UV production is effective and air is more effective as feed gas than ammonia or argon. In the cases of Radio frequency generation, the gas ionization take place through rapidly cycling electrical impulses, operating at various power and voltage settings. Power of 100-400 W is possible using hydrogen, argon and oxygen.
  • Vacuum processing highly encourage, as it is an easier ionization condition.
  • Both alternating current and direct current system are possible. The first one is easier to integrate into conventional power.

(Niemira, 2014)

  • There are two typical generation techniques of plasma: The first one is Pulse discharge plasma, generally used in large scale with a spiral electrode, it needs a power of 500 KV. The other technique is Surface discharge plasma, excellent to generate good plasma but noisy and expensive, the generation of O3 is concerning.

(Muredzi, 2012)


Changes in process (Operation Unit Applications)

Pasteurization

One of highest potential of plasma technologies in the food industry is in the pasteurization process because of the effect of simultaneous inactivation mechanisms:

1) Direct interaction cells with reactive species and charged particles.

2) UV damage of cellular components and membranes.

3) UV-mediated DNA strand breakage.

(Niemira, 2014)


Case:

Inactivation of Staphylococcus aureus on the beef jerky by radio-frequency atmospheric pressure plasma discharge treatmentOriginal Research Article

Innovative Food Science & Emerging Technologies, Volume 22, April 2014, Pages 124-130

Joo-Sung Kim, Eun-Jung Lee, Eun Ha Choi, Yun-Ji Kim


Blanching

Pretreatment and enzyme inactivation enabled by plasma technology avoiding conventional thermal treatment. The quality of freshly cut fruits and vegetables mainly depends on the activity of naturally occurring enzymes, which catalyse browning reactions at surfaces. Understanding of cold plasma effects on enzyme activity and could be a foundation for a possible industrial implementation.

(Surowsky, Fischer, Schlueter, Knor, 2013)


Cleaning of bottles and cases

The application of plasma for surface cleaning has relevant applications for packaging cleaning and for post-harvest. It helps to avoid any post-process recontamination or hazards from the package itself. In-package DBD plasma is a novel and innovative approach for the decontamination of foods with potential industrial application.

(Pankaj et all, 2014)

Plasma-based sanitation technique for fresh fruits and vegetables can also be implementable into running process lines without detrimental effects to product quality. There is also antibacterial capacity of cold plasma on different produce surfaces.

(Baier et al, 2013)


Energy Savings

  • Improve Energy Efficiency due to the combined effect of different sterilization mechanism leading to a lower production time, this is less energy per production unit.


Change in Energy Distribution

  • Use of electricity instead of the conventional thermal treatment.


References

  • Baier, M., Görgen, M., Ehlbeck, M., Knorr, M., Herppich, W., Schlüter, O. (2013) 'Non-thermal atmospheric pressure plasma: Screening for gentle process conditions and antibacterial efficiency on perishable fresh produce', Innovative Food Science & Emerging Technologies, 22(April), pp. 147-157.
  • Muredzi, P. (2012) 'Chapter 9: Gas, Cold Plasma Technology', in Aleman, M. (ed.) Emerging Non-thermal Food Processing Technologies. USA: CBH books, pp. 199-213.
  • Niemira, B. (2014) 'Part III: Other non-thermal processing techniques: Chapter 18: Decontamination of food by Cold Plasma', in Sun, D. (ed.) Emerging Technologies for Food Processing. UK: Academic Press, pp. 327-332.
  • Pankaj, S., Bueno-Ferrer, C., Misra, N., O´Neill L., Jiménez, A., Bourke, P., Cullen, P. (2014) 'Characterization of polylactic acid films for food packaging as affected by dielectric barrier discharge atmospheric plasma', Innovative Food Science & Emerging Technologies, 21(January), pp. 107-113.
  • Surowsky, B., Fischer, A., Schlueter, O., Knor D. (2013) 'Cold plasma effects on enzyme activity in a model food system', Innovative Food Science & Emerging Technologies, 19(July), pp. 146-152.



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