Worldwidedemand for food is expanding and will probably keep on going for decades,impelled by 2.
3 billion person incrementin world population along with increase in per capita wages through middle ofthis century (Godfray et al., 2010). So preservation of foodmaterial is need of an hour. The primary goal of food preservation technologiesis to control and eliminate microorganisms along with maintaining the qualityand nutritional value of food. Till now food industries are using many thermaltechnologies for food preservation but over past several decades, industriesare heading towards novel non thermal technologies to reduce the thermal impactof heat based technologies This move is credited to different reasons,including (1) consumer demand for safe and nutritious food products; (2)process and energy efficiency; and (3) legislative and regulatory requirementsaiming to minimize the use of chemical preservatives (Ojhaet al.
, book chapter). Several novel coldprocessing technologies are introduced including irradiation, high pressureprocessing (HPP), ultrasound, pulsed electric field, radio frequency etc. butprocesses requires specializedequipment, trained personnel and expensive too (Yun et al., 2010) Cold plasma isan innovative technology which recently been used in biological treatmentsincluding sterilization and surface modification (Rodríguez et al., 2017). Reactiveoxygen species (ROS) like singlet oxygen, ozone, energized molecular nitrogenare produced by cold plasma (Misra et al., 2014).
which helps in inactivation of several spoilagemicroorganisms and food borne pathogens. (Brun et al., 2010; Niemira, 2012). Several studiedshowed that the effective microbial destruction like inactivation of Escherichiacoli from fresh produce (Bermudez-Aguirre, 2013), Aspergillusparasiticus and Penicillium sp from seeds of various vegetable,legumes and cereals (Selcuk, 2008), Erwiniacarotovora in potatoes(Moreau, 2007), Listeria monocytogenes from plastic trays, paper cupsand aluminum foil (Yun, 2010).Thistechnology has successfully employed for surface decontamination of fresh meat,poultry, fish, and fruits and vegetables (Fernandez et al., 2013; Noriega etal., 2011; Ziuzina et al., 2014) and surface disinfecting of packaging material and enhancing functionalproperties of these materials.
(Güleç et al., 2006; Lee et al., 2015; Ozdemir et al.,1999; Pankaj et al., 2014). As cold plasma technology currentlytrending area of research and liitle exploited by food industries so the aim ofthis article is to provide current review of this innovative technologies, itsapplications and significance in food industries and future scope of nonthermal technologies for food preservation.
Princple /Mechanism Incold plasma technology plasma generation is the first and important step. Plasma,a fourth state of matter is fully ionised gas composed of various substanceslike electrons, free radicals, photons and excited state atoms with neutralcharge (Ekezie et al., 2017; Dasan et al., 2017).
Theseplasma particles have equal number of positive and negative ions thus possessingnet neutral charge. (Kudraand Majumdar, 2009). Thermal and non thermal plasma two classification ofplasma are based on generation mechanisms of inducing varying temperature andpressure by energizing neutral gas. Thermal plasma requires high pressure (>105 Pa) and up to 50 MW of energy for itsproliferation, which is likewiserecognized by a thermodynamic harmony between the electrons and heavier speciesbecause of uniform gas temperature for all constituents (Scholtz et al.
, 2015). While non thermal plasma also known as near ambient temperatureplasma (NTP) is produced under atmospheric pressure at temperatures of30-60°C requiring low power. These plasma do not require localized thermodynamicequilibrium and hence known as non-equilibrium plasma. When a high voltage isapplied on food material atmospheric gas get ionised and producing reactiveionised species (ROS) , the microorganisms present inside the food material receivedradical bombardment which provokes the lesions on the surface of cell that arenot healed by microorganisms and thus starts cell lysis. The accumulationelectrostatic forces on cells surface leads to lesion formation. This phenomenonis known as etching. Along with microbial destruction ROS also interact with vital cellularbiomolecules, such as DNA, proteins and enzymes in cell. It also formsunsaturated fatty acid peroxides from lipids and oxidise amino acids.
(Misraet al., 2016) Applications: Microbial destruction:Microbial inactivation willaffect several quality parameters of food. The interaction of plasma ions withmicrobial cells made it a inevitable processing technique with little damage tofood nutrients.
Its antimicrobial efficacy had been studied on wide rangeon microorganisms (Dasan et al., 2017; McClurkin-Moore,Ileleji, & Keener, 2017; Wang, Zhuang, & Zhang, 2016; Xu et al., 2017). Plasma reactive reactive interacts with DNA resulting information of malondialdehyde (MDA) whichforms DNA adducts and thus damaging the microbial cells. These plasma speciesalso interacts with water forming OH* ions which are highly reactive andharmful. These ions forms hydration around DNA and damaging 90% of it. Hydroxyl radicals also reacts with othercell components leading to chain oxidation which will damage them along withcell membranes. (D.
Dobrynin, G. Fridman, G. Friedman, A. Fridman doi:10.
1088/1367-2630/11/11/115020), The significantreduction in E.coli and L.monocytogenes was studied on red chicory (Cichoriumintybus) keeping stableconditions with 22°C temperature, 60% RH, varying time for 15 and 30 min andkeeping food material at 70mm difference from discharge of cold plasma (Pasqualiet al., 2016).
Choi et al. (2017) showed the effect of coronadischarge plasma on dried squid at 20 kV (58kHz) for 0 to 3 min and 2.0, 1.6 and 0.9 log reduction was observed for aerobicbacteria, marine bacteria and Staphylococcus aureus, respectively with veryless nutritional changes. The 40 min duration of microwave induced cold plasma significantlyinhibit B. cereus, A.
brasiliensis, and E. coli O157:H7 by 2.1, 1.
6 and 1.9 log CFU/cm2,respectively, after 21 days against onion powder without affecting color andantiodiant property of sample (Kim, Oh, Won,Lee, & Min, 2017). Packaging material Packaging materialsare solely responsible food materials protection during handling, transportationand distribution. So a good packaging material with better sustainability and functionalityprovide better protection to food materials inside it. The innovative plasmatechnology providing high potential in food packaging as it improves adhesionproperties, polymerization and aids in good printability (Pankaj et al.,2013).
This technology helps in external decontamination of packaging material (Shakilaet al., 2012), improved fuctionalization, etching and deposition as plasma isstreaming all round the surface. Surface fuctionalization involves inclusion offunctional groups and turnable surface energies tomaterial with a specific end goal to affect antimicrobial properties andupgrade mechanical properties (Contini etal., 2014; Pankaj et al., 2014; Sen & Mutlu, 2013). It also helps in keeping up sealing properties of polymerfoils or laminates (Heise, Neff, Franken, Muranyi,& Wunderlich, 2004).