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Optical emission spectroscopy characterisation of plasma reactors for liquid food treatments

Traditional food preservation techniques, involving thermal processing, have detrimental sideeffects regarding the nutritional composition of fruit juices. This is especially relevant for aromatic profile and composition of bioactive/functional components. Therefore, in the recent years, there has been an extensive research aimed towards the development of new nonthermal methods that would effectively inactivate undesirable microorganisms (bacteria, yeasts and molds) and preserve the nutritional value of the food. These new methods include, among others, exposing the food to the high pressure, high power ultrasound, pulsed light, oscillating magnetic fields, pulsed electric fields and cold plasma. The aim of this study was to investigate relative composition of the cold plasma, its electron and heavy particle temperatures and possible chemical pathways leading to observed molecular species. These properties have been measured for different plasma reactor designs, working gases and electrical conductivity of the treated water using optical emission spectroscopy. The working gases were argon and compressed air, while the conductivity of water was adjusted by adding NaNO3.The plasma was generated using a pulsed high voltage DC source (30 kV, pulse duration 100 ns), at a discharge frequency defined by rotating spark gap at 30-250 Hz. Preliminary measurements show that this kind of atmospheric plasma discharge leads to significant dissociation of N2 and OZ ; emission spectra are abundant in N2, N, N, 0, 0", H lines. Lower electrical conductivity of the water generally leads to higher emission intensity. Regarding the type of the working gas, argon was found to decrease the width of emission lines and at the Same time to increase the background continuum radiation. This work was supported in part by Croatian Science Foundation under the project #2753 and the project P-11-2013- 6248 [1] I. Elez Garofulić, A. Režek Jambrak, S. Milosevic, V. Dragović- Uzelac, Z. Zorić, Z. Herceg LWT Food Sci. Technol. 62 (2015) 894-900 [2]_T. Vukušić. M. Shib. Z. Herceg, S. Rogers, P. Estifaee, S. Mededovic Thagard, lnnov. Food SCI. Emerg. 38 (2016) 407-41 3

Optical emission spectroscopy, liquid plasma reactor

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