Non-thermal Processing with Plasma Technologies Brendan A. Niemira Food Safety and Intervention Technologies Research Unit U.S. Department of Agriculture, Agricultural Research Service Eastern Regional Research Ctr. 600 E. Mermaid Ln, Wyndmoor, PA, USA
Cold plasma: this isn’t it B.A. Niemira .
Non-thermal plasma • What is a plasma? – Fourth state of matter – Equivalent to a highly energetic form of ionized gas ENERGY ENERGY ENERGY SOLID LIQUID GAS PLASMA • Why is it sometimes called “cold” plasma? – For food processing, intended to operate at conventional room temperatures B.A. Niemira
Non-thermal plasma • Inputs to the system – energy (electricity, microwaves, etc.) – carrier gas: air, a pure gas (He, O 2 , N 2 , etc.) or a defined gas mixture • Output – self-quenching plasma – resolves to UV light and ozone – chemical residues are expected to be minimal to non-existent • New technology for food processing – adaptation from existing applications – regulatory status B.A. Niemira
Non-thermal plasma Free Elemental e - radicals Oxygen NO x Ozone UV light Nanoparticles Injected volatiles Oxygen Nitrogen Carbon dioxide B.A. Niemira
Making cold plasma: gas and pressure One atm., 760 torr pd = pressure*distance between parallel plates
Making cold plasma: gas and pressure Higher voltage required; equipment = $$$ Ease of ionization Lower volatage required; Cost of feed gas equipment = $ $ $$$$$ $$$ N 2 , Air H 2 He, Ne, Ar
Non-thermal plasma: technologies • Remote treatment and enclosed chambers • Contact with electrodes, corona discharges • Direct applications • In-package treatments B.A. Niemira
Enclosed plasma treatment chambers OAUGDP (Kayes, M.M. et al., 2007. Foodborne Path Dis 4(1). DOI: 10.1089/fpd.2006.62)
Enclosed plasma treatment chambers Microwave pumped plasma, enclosed chamber (Amidi, M., et al. 2007. Food Science Australia)
Electrode contact plasma treatment air nitrigen co2 argon 1.00E+07 1.00E+06 1.00E+05 Survival counts 1.00E+04 1.00E+03 1.00E+02 1.00E+01 1.00E+00 0 5 10 15 20 25 30 35 Treatment time (second) 0 0 10 20 30 40 -0.5 -1 -1.5 Dielectric barrier discharge, Log(N/No) -2 applied to E. coli on almonds -2.5 16 kV -3 (Deng, S. R. et al. 2007. J. Food Sci. 20 kV -3.5 72(3):M62-M66.) 25 kV -4 -4.5 Time (s)
Direct application of plasma, open air (Niemira and Sites. 2008. J Food Prot.)
USDA-ARS cold plasma research subjects
Direct application of plasma, carrier gas Honeydew Mango Feed gas: 99.5% He, 0.05% O 2 Perni, S. et al. 2008. JFP, 71(2):302–308
In-package treatments: ozone generation E. coli O157:H7 inactivation on spinach (Klockow, P.A., K. Keener. 2009. LWT) “Electrodes were placed above and below the bag, oriented on top of each other to allow for maximum ozone production. Electrodes rested on top of each other with the bag in between having an approximate gap distance of 3-3.5 mm [1/8 inch]. The system was then activated for a 5-min treatment.” “Treated samples showed varying levels of discoloration”
In-package treatments: ozone generation • PlasmaLabel. (Schwabedissen, A. et al. 2007. Contrib. Plasma Phys. 47 , 551-558 ) • Electrically conductive labels on (+) inside surface – Rigid container, clamshell, bag, etc. • Cold plasma generated by induction • 4 log cfu reduction of B. subtillis on agar, 10’ treatment. – Ozone concentration inside the package to 2000 ppm (-) • Sensory impact? • Optimization – shape of the applied electrodes – method of application (screen- printed, applied, bonded, etc)
Plasma treatment of liquids • Air plasma microjet in a quasi-steady gas cavity – reduces pH to 3.0-4.5 after 10’. - & NO 2 - increases to 37 mg · L −1 and 21 mg · L −1 – NO 3 after 20’ – Suspended Staphylococcus aureus inactivated by pH 4.5. – Mode of action: perhydroxyl radical (HOO•) reaction with cell membranes (Liu et al, 2010, Plasma Processes and Polymers 7(3-4):231-236) • Thin film application • Continuously renewed liquid surface • Co-injected spray into plasma discharge – Can yield H 2 , H 2 O 2 or NO x , depending on plasma feed gas (Burlica et al., 2010. Ind. Eng. Chem. Res., 49(14):6342–49) B.A. Niemira
Commercial Equipment Ingersoll-Rand PlasmaTreat Enercon Industries
Non-thermal plasma: conclusions • Many different ways to make plasma • How well it works is determined by: – Type of plasma – Nature of power delivered – Feed gas composition • What are you trying to achieve? • What product are you trying to treat? • What kind of packaging are you using? B.A. Niemira
Brendan.Niemira@ars.usda.gov www.tinyurl.com/Niemira B.A. Niemira
Non-thermal plasma: technologies A. remote exposure reactor (Gadri et al., 2000) B. plasma pencil (Laroussi and Lu, 2005) C. plasma needle (Sladek and Stoeffels, 2005) D. gliding arc (Niemira et al., 2005) E. microwave plasma tube (Lee et al., 2005) F. dielectric barrier discharge (Deng et al., 2005) G. resistive barrier discharge (Laroussi et al., 2003)
NTP Technology Class I. Remote treatment II. Direct treatment III. Electrode contact Nature of NTP applied Decaying plasma (afterglow) Active plasma - short and Active plasma - all chemical - longer lived chemical long-lived species species, including shortest species lived and ion bombardment NTP density and energy Moderate density - target Higher density - target in the Highest density - target remote from electrodes. direct path of a flow of active within NTP generation field However, a larger volume of NTP NTP can be generated using multiple electrodes approx. ≤ 1 cm; arcing can Spacing of target from NTP- Approx. 5 - 20 cm; arcing approx. 1 - 5 cm; arcing can generating electrode (filamentous discharge) occur at higher power occur between electrodes unlikely to contact target at settings, can contact target and target at higher power any power setting settings Electrical conduction through No Not under normal operation, Yes, if target is used as an target but possible during arcing electrode OR if target between mounted electrodes is electrically conductive Suitability for irregular High - remote nature of NTP Moderately high - NTP is Moderately low - close surfaces generation means maximum conveyed to target in a spacing is required to flexibility of application of directional manner, requiring maintain NTP uniformity. NTP afterglow stream either rotation of target or However, electrodes can be multiple NTP emitters shaped to fit a defined, consistent surface Examples of technologies Remote exposure reactor, Gliding arc; plasma needle; Parallel plate reactor; plasma pencil microwave-induced plasma needle-plate reactor; tube resistive barrier discharge; dielectric barrier discharge
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