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Biopolymers have intrinsic drawbacks compared to traditional plastics, such as hydrophilicity, poor thermo-mechanical behaviours, and barrier characteristics. Therefore, biopolymers or their film modifications offer a chance to create packaging materials with specified properties. Cold atmospheric plasma (CAP) or Low temperature plasma (LTP) has a wide range of applications and has been used in the food industry as a potent tool for non-thermal food processing. Though its original purpose was to boost polymer surface energy for better adherence and printability, it has since become an effective technique for surface decontamination of food items and food packaging materials.
No. | Plasma Treatment Conditions | Matrix and Fillers; Composite Type | Applications | Effect of Plasma Treatment on Properties | References |
---|---|---|---|---|---|
1. | Dielectric barrier discharge (DBD) cold plasma, for 5, 10 and 15 min. Maximum transmission power: 50 W; Voltage: 15 kV; Current: 10 mA; Frequency: 50 kHz; Power source: DC pulse type with pulse width modulation (PWM) |
Chitosan + cellulose nanoparticles; Films | Packaging of strawberry | For films: Improved mechanical properties (TS & EAB), water vapour permeability, oxygen transmission rate, moisture content and water contact angle. For substrates: Enhanced mechanical properties (firmness and Young’s modulus), chemical attributes (pH, soluble solid content and total ascorbic acid), physical characteristics (weight loss and colour features), microbial activities (bacteria, yeast and mould) |
[10] |
2. | Open-air DBD cold plasma. Peak voltage: 20 kV; Frequency: 20 kHz | Polylactic acid multilayer films | Active packaging of sunflower oil and “pesto” sauce; Biodegradable multilayer active packaging, to extend food products shelf-life and/or maintain high quality levels of oily foods during storage. | Immobilization of oxygen scavenger agent (ascorbic acid); Decreased oxidation kinetics; Better and more stable quality characteristics in terms of colorimetric, microbiological and textural parameters | [12] |
3. | DBD cold plasma, for 60 and 120 s. Gas source: Air; Argon gas type, oxygen gas pressure of 0.4 millibars equivalent to 0.3 Torr and power of 89 watts equivalent to radiometric waves |
Chitosan solution | Preservation of quality and safety (shelf life) of pistachios during storage | Significant reduction in the amount of aflatoxin, mold and yeast after 120 days; Physicochemical characteristics of pistachios did not change significantly; No adverse effect on the sensory characteristics of pistachios | [13] |
4. | Atmospheric air cold plasma treatment for 5, 10 and 15 min in the excitation mode. Input voltage: 6.2 kV; Power level: 60 kW; Pulse frequency: 10 kHz |
Wild almond protein isolate (WAPI) + Persian gum (PG); Films | Edible films in food packaging | Progressively improved mechanical properties (increased thickness, TS and EAB); No significant effect on WVP and solubility; Surface roughness directly proportional to plasma treatment time, but surface remained integrated; Best results obtained for films with 10 min treatment; Properties tend to deteriorate after 15 min treatment | [14] |
5. | Dielectric Barrier Discharge Atmospheric Cold Plasma (DBD–ACP); Fixed exposure time (3 min) with varying voltages of 10, 20, 30, 40, and 50 kV; Fixed voltage (30 kV) with varying exposure times (1, 2, 3, 4, 5 min) | Soy protein films | Edible packaging and food preservation | Increased water interactive properties and thermostability; Decreased surface roughness; Effects of different ACP treatment times too | [15] |
6. | Cold plasma based on helium. Glow discharge reactor at 13.56 MHz. Chamber vacuum: <8 Pa. Treatment with He: Self-bias voltage −100 V; Treatment time: 10 min. Treatment with HMDSO: Self-bias voltage −60 V; Treatment time: 20 min |
Hexamethyldisilox-ane (HMDSO) treated extruded corn starch films | Barrier films for food packaging and pharmaceutical products | More homogeneous coating and smaller granules; Increased hydrophobicity, but roughness created by helium plasma was not effective in increasing the water contact angle of the modified surface; No much effect on water vapour permeation; Significant reduction in absorbed water content, mostly due to the formation of a barrier to water absorption of around 80%; Physical barrier to water, while allowing permeation to water vapour | [16] |
7. | DBD cold plasma treatment. Voltage: 20 kV; Excitation frequencies: 50, 400 and 900 Hz; Treatment time: 5 min |
Starch, gelatin and bacterial cellulose films | Sustainable and biodegradable alternatives for plastic packaging | Improved hydrophobicity, surface morphology, tensile strength, and elasticity module; Reduced water solubility; Pronounced changes for starch films at low excitation frequency (50 Hz) of plasma, and for gelatin and bacterial cellulose films at high excitation frequency (900 Hz) |
[17] |
8. | Cold plasma treatment. Vacuum plasma reactor. Frequency: 13.56 MHz; Pressure: 0.0643 Torr; Power: 30 W; Treatment time: 60 s | LDPE + Myristica fragrans Essential Oil (MFEO); Films | Active food packaging material | Cold plasma treatment improved the properties of LDPE films by facilitating MFEO coating | [18] |
9. | Surface dielectric barrier discharge (SDBD) plasma from Plasma Assisted Sanitation System (PASS) for 5 and 10 min. Gas: Environmental air; Relative humidity: 20–40%; Voltage: 1–20 kV; Frequency: 1–20 kHz; Tunable duty cycle: 1–100%. Imposed voltage: 6 kV; Frequency: 5 kHz; Fixed duty cycle: 100% |
Polyethylene terephthalate (PET) trays (350 microns thick) and polypropylene (PP) film (69 microns thick) |
Newly developed plasma sanitation system for food packaging decontamination from SARS-CoV-2 RNA | Plasma treatment decontaminated virus, without significantly affecting the properties of packaging and food substrate; 5-min treatment reduced detected RNA for both surfaces, but to different extents. Indicated that interaction between reactive species and viral genetic material is affected by the matrix; 10-min treatment completely degraded RNA molecules from both surfaces | [19] |
10. | Plasma activated water (PAW) produced using surface barrier discharge (SBD) sourced high voltage cold plasma (CP). Sinusoidal signal frequency: 18 kHz; Atmospheric pressure; Plasma-inducing gas: Room air |
Sodium alginate films | Food packaging | Increased TS, tensile modulus, EAB, LVE region and storage modulus; No intersection between G′ & G″; Showed shear thinning properties or non-Newtonian behaviour; decreased WVTR | [20] |
11. | Cold plasma treatment. Treatment time: 30 s; Power: 350 W; Nitrogen flow rate: 100 standard cubic centimeters/min (sccm) | Momordica charantia polysaccharide (MCP) nanofibre + Phlorotannin (PT); Electrospun nanofibre membranes | Active food packaging | Increased release efficiency of PT, resulting in an increase in antibacterial and anti-oxidant activities, without the alteration of chemical structure | [21] |
12. | DBD cold plasma. Voltage changed group adjusted at a changed treatment of 0, 30, 40, 50, 60 and 70 V under the duration of 60 s. Time changed group subjected to a sustaining time of 0, 15, 30, 45, 60, 90 and 120 s under the voltage of 50 V; Current: 2 ± 0.2 A |
Casein edible films | Packaging material | Crystalloid migration and casein aggregation (via SEM) leading to reinforcement of structure stability; Slight change in crystal structure (via XRD); Stable state of molecular structure (via FTIR); Remarkable improvement in packing characters (including mechanical and barrier properties); Slight modifications of colour and transparency; Rearrangement in order of protein chains | [22] |
13. | Carbon tetrafluoride (CF4) reactive-ion etching (RIE) using 13.56 MHz radio-frequency plasma equipment. Flow rate: 3 sccm; Working pressure: 3.0 × 10−2 Torr; Treatment time: 4 min; Power: 100 W | Transparent, colourless and self-disinfecting polyethylene terephthalate (PET) film that mimics the surface structure of Progomphus obscurus (sand dragon) wing, physically killing the attached bacteria | Antibacterial overcoating with good optical properties for contactable surfaces in private and public interior spaces and packaging applications | Introduction of nanopillars; Improved optical properties (transparency and colourlessness); Notable enhancement in antibacterial activity against S. aureus and E. coli by activating or strengthening physical biocidal action | [23] |
14. | Cold plasma (CP) generated by dielectric barrier discharges (DBD) plasma reactor. Voltage: 60 V; Current: 1.5 A. Short-term treatment time: 60 s; Long-term treatment time: 120 s |
CP pre-treated zein films + Porous PLA layer coating by breath figure self-assembly | Biodegradable packaging | Better-ordered porous structure after coating with PLA; Induced compatibility between zein and PLA molecules, by changing the protein conformation and by enhancing the intermolecular hydrogen bonding interactions; Significant improvement in surface hydrophobicity, fracture resistance, water vapor barrier, and thermal stability; Improved UV barrier and excellent biodegradability; Potential to enhance adhesion and improve functionalities of porous coating on other biopolymer materials | [24] |
15. | DBD atmospheric air cold plasma (at ambient temperature and atmospheric pressure). Plasma discharge frequency: 50 Hz; Voltage: 31 kV; Treatment time: 1, 5, 10, 15 and 20 min | Polycaprolactone (PCL) or poly(lactic acid) (PLA) and cassava starch multilayers | Multilayer packaging materials | Increased hydrophilicity and surface roughness; Improved adhesion between layers, zeta potential, delamination resistance, etc. | [25] |
16. | Cold plasma treatment. Power: 400 W; Treatment time: 4 min; Nitrogen flow rate: 100 sccm | Silk fibroin nanofibers + Cold plasma treated thyme essential oil (TO) composite films, post-treated with cold plasma | Effective antimicrobial packaging to increase shelf life of foods |
Increased antibacterial activity by increasing TO release amount, due to surface modification, but without affecting chemical composition of the films; Decreased number of Salmonella Typhimurium in chicken and duck meat |
[26] |
17. | DBD-50 cold plasma reactor. Power: 100 W; Treatment time: 30, 60, 90, 120 and 150 s | Zein + Chitosan films | Food and pharmaceutical packaging materials | Improved wettability, TS, EAB, water vapour barrier and thermal stability; Secondary structure of zein molecules became ordered; Rougher surface morphology, increased surface free energy and enhanced hydrogen bond interactions between zein and chitosan after plasma treatment (optimum range: 60–90 s) | [27] |