Characteristics of Eco-Friendly Nanocomposie Films Based on Basil Seed Mucilage Rainforced with Carboxymethyl Cellulose and Nanoclay

Introduction: The seeds of Ocimum basilicum L., also known as basil, include a remarkable content of mucilage with great functional properties. According to literature, two major fractions of glucomannan (43 %) and xylan (24.3 %) are the main polysaccharidic components of basil seed mucilage (BSM). Some outstanding advantages of BSM such as biocompatibility, low production cost, hydrophilicity, biodegradability and worthy rheological properties are qualified it for making edible films and coatings. One of the most important ether derivatives of cellulose is carboxymethyl cellulose (CMC) accompanied by many applications in the pharmaceutical, cosmetics and food industries. Also, CMC is a good material for synthesis edible film or coating because of efficient barriers to oils, gases and aromatic compounds. In order to reform the defects of biopolymeric packaging films, researchers have loaded different nano-scale materials into the films matrix. As a result, mechanical, thermal and barrier traits of the produced nanocomposites considerably improved in comparison with conventional composites and unmodified biopolymers. Layered silicate clays have been received much attention for use as nanomaterial due to their more availability, low cost and biocompatibility. In the recent two decades, montmorilonite was incorporated into the films from various sources such as hydrophilic biopolymers (starch, chitosan and CMC) for improvement of the mechanical and barrier properties against water vapour, oil, aroma, etc.
Materials and methods: Firstly, mucilage extraction from basil seeds (T = 50 °C, soaking time = 20 min, water to seed ration = 50 : 1) was carried out, mucilage purified and dried at 50 °C for 48 h. BSM net film (T1) was fabricated from mixing of 0.4 g BSM powder with glycerol as plasticizer (100 % w/w BSM powder) by casting method. Blended films were made from combination of BSM powder and CMC (100, 162.5 and 225 % w/w of mucilage powder) as T2, T3 and T4 treatments. For preparation of nanocomposites, a nanoclay suspension was prepared, gradually added at constant concentration of 8 % w/w to T2, T3 and T4 film solutions. After drying of casted film solution on polypropylene moulds, the casted films were conditioned and used for next examinations. Water vapour permeability (WVP) of the films was measured by ASTM E 96 - 00 method. Solubility in water was determined by Zahedi et al (2018) and water uptake was evaluated by method of Fathi-Achachlouei and Zahedi (1397). A colorimeter was used to determination of L* a* b*. Opacity and light absorbance of the films were assayed by a UV - Visible spectrophotometer at 200 to 800 nm wavelengths. Crystallinity of the nanocomposites was investigated by X - ray diffraction at 2Ɵ = 10 - 80 °. The experiments were performed at a completely randomized design, and results were analyzed using one-way ANOVA.
Results and discussion: Results showed that WVP of BSM film was the maximum and it was reduced significantly due to CMC addition, and by incorporation of MMT more than two times decrease for WVP was recorded (p < 0.05). The BSM film showed the maximum solubility in water due to hydrophilic nature, that was gradually decreased by rainforcement of film matrix via loading of CMC and MMT materials (p < 0.05). An increased water solubility is a favourite trait when a film is discarded in the nature because of an accelerated biodegradability. The moisture uptake of control film reduced from 95 to 63 % by adding 225 % CMC, and continuously reduction up to 58 % took placed at simultaneuous presence both of CMC and MMT (p < 0.05). A decreased water uptake is of importance when application of films on hygroscopic foods. Employment of different ratios of CMC and MMT did not significantly change L* and a* color values, while b* values of nanocomposite films indicated a decreasing trend with increasing CMC (p < 0.05). BSM film had a opaque appearance, and opacity was positively influenced by both of CMC and MMT so that T7 nanocomposites were 5 orders transparent than that of the control films. The efficiacy of all films for UV absorption was very higher than visable region, and the maximum light absorption obtained at 230 - 240 nm. BSM films superimposedly absorbed more light at both UV and visable regions, and light absorption remarkably reduced by CMC addition because net CMC films are basically transparent. XRD spectra of MMT and CMC powders showed a crystaline and semicrystaline structure, respectively. For the films, XRD spectra revealed a semicrystaline structure for BSM films, and crystalinity was increased to some extent by loading nanomaterials.
Conclusion: Simultaneous employment of CMC and nanoclay improved all physicochemical properties of basil seed mucilage-based biodegradable films, with the minimum negative effects because of hydrophilicity of CMC and heterogenicity of nanoclay. Take together, the treatment with the most content of CMC and montmorillonite (T7) showed the best results among the treatments and we can advice for application in primary packaging of different foods and decrease the layers of packaging.