Packaging materials represent the largest category of plastic waste, since almost 50% of global plastic waste comes from the packaging field. The compound annual growth rate (CARG) for global plastic waste is 5.4% from 2022 to 2030. Edible food packaging has been investigated as an alternative, environmentally friendly method to maintain food freshness and extend shelf-life (Galus et al., 2020).
However, packaging materials based on natural biopolymers often exhibit poor barriers and mechanical properties. For this reason, other components such as crosslinkers may be used to enhance barriers, and mechanical properties (Otoni et al., 2017). Crosslinking agents improve the mechanical and barrier properties of the films based on proteins and polysaccharides. When a crosslinking agent is added to the matrix of the polymer, a three-dimensional structure is synthesized by binding the polymer chains with covalent or non-covalent bonds, resulting in more hydrophobic films (Garavand et al., 2017).
Polysaccharides can be effectively used to synthesize biobased packaging materials, due to their biodegradability and biocompatibility. Among biopolymers, cellulose, and its derivates have been reported for their applicability in the packaging field, as cellulose-based films are odorless and tasteless. Carboxymethyl cellulose (CMC) is produced by adding carboxymethyl group (CH2COONa) groups in cellulose molecules to obtain a water-soluble molecule. CMC-based films are biodegradable, but they exhibit poor barrier properties due to the hydrophilic nature of cellulose (Yildirim-Yalcin et al., 2022).
Plasma is an ionized gas containing electrons, photons, and atoms and it can be categorized as high temperature and low-temperature plasma. Cold Atmospheric Plasma (CAP) has been used in the packaging sector to improve the mechanical and barrier properties of polymers. Surface treatment of polysaccharide-based films using CAP may improve their functionality of the developed films (Zhu et al., 2021).
The objective of the study was the development of a novel polysaccharide-based and crosslinked, edible packaging film appropriate for fish and seafood. CAP was used as a surface modification method to enhance the barriers of the developed films. Fresh meagre fillets under refrigeration were selected as the case study.
Materials and methods
2% CMC-based films were produced according to the solvent casting method and glycerol was added as a plasticizer. Calcium cations (Ca+2) were added as a crosslinking agent at the concentrations of 1% and 2%. The produced films were treated with CAP (kINPen® IND, neoplas GmbH, Germany) with continuous flow (argon, 4 L/min) for 5 and 10 min. Films without the crosslinking agent and plasma treatment were produced and tested as controls. Water Vapor Permeability (WVP) and Water Vapor Transmission Rate (WVTR) were evaluated according to ASTM E96/E96M. The hydrophilicity of the surface of the films characterized through contact angle with Theta Flow Optical Tensiometer (Biolin Scientific, Gothenburg, Sweden). The mechanical properties were measured according to ASTM D882 (ASTM, 2001), by Instron 3400 (Norwood, MA, USA) and load 50 Ν. The color changes of the films before and after plasma treatment were recorded. CMC-based films were applied on fresh meagre fillets (Argyrosomus regius) stored isothermally at 2°C for shelf-life evaluation, based on Total Viable Count (TVC) and Pseudomonas spp. growth and compared with the respective data obtained for conventional Polyvinyl chloride (PVC) films.
The results for the water barriers showed that by adding Ca+2 to CMC film forming solution the produced films had lower WVTR and WVP. The WVTR for CMC-based films was 1206.73±66.24 g/day× m2 and reduced to 973.98±82.81 g/day× m2 and 869.88±282.10 g/day× m2 for films with 1% and 2% Ca+2, respectively. All the produced films had higher water barriers after CAP treatment. The WVTR for the CMC-based films was 1206.73±66.24 g/day× m2. After 5 minutes CAP the WVTR was 1107.01±127.61 g/day× m2 and after 10 minutes of CAP treatment the WVTR was 1080.25±157.08 g/day× m2. Similar trend was observed after CAP treatment for the films with the crosslinking agent. The contact angle of CMC based films was 60.25±8.04° represented hydrophilic materials. CAP treatment resulted in reduced contact angle (44.28±2.63° and 37.06±4.31° for 5 minutes and 10 minutes CAP, respectively). The addition of 1% Ca+2 led to increased contact angle of films (64.33±9.90°) but when 2% Ca+2 was added the contact angle was lower (47.69±3.81°). Films with Ca+2 had also lower contact angle after CAP treatment. The addition of Ca+2 into the CMC film-forming solutions led to more brittle films at higher concentrations (1.5 and 2% Ca+2). When 1% of Ca+2 was added, the young’s modulus of the films reduced from 3120.51±672.76 MPa to 2505±516.56 MPa for CMC-based films and CMC/1% Ca+2-based films, respectively. The tensile strength and the elongation at break were not statically different for the two types of the films. The color of the produced films did not change by adding the crosslinking agent or after CAP treatment. The replacement of conventional PVC films with the developed CMC-based films did not affect the microbial growth of meagre fillets during refrigerated storage, resulting at shelf-life of 10 days at 2°C (same for all the tested conventional and alternative packaging films).
Discussion and conclusion
The results of the study show the potential of CMC-based, edible packaging films for the effective preservation of chilled fish, without affecting quality and shelf-life. The appropriate design of polysaccharide-based films and surface modification for the enhancement of the barriers and mechanical properties of the developed packaging systems will contribute to the sustainability of the aquaculture sector towards a zero-waste future.
This study was supported by the Greek Operational Programme for Fisheries, Priority Axis “Innovation in Fisheries”, Project title: “Design and development of innovative packaging materials with enhanced protective activity for fisheries and from biodegradable materials using fish by-products (pack4fish)” (2021-2023) MIS5074718, website: http://pack4fish.aua.gr
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