Preparation and identification of carrageenan/nanoclay nanocomposite films containing Peganum harmala extract

Films manufactured by nano materials, biopolymers or so-called biopolymer nanocomposites exhibit desirable functional properties. Nowadays, various polysaccharides, such as cellulose, pectin, starch, marine algae and gum, are used in film production. Carrageenan is one of the natural polysaccharides that have been extensively studied in the field of the production of foods and protective coatings against drying, light and oxygen (Rhim & Wang 2014). One of the existing methods for producing active food packaging is the addition of active ingredients, including antimicrobial and antioxidant agents to packaging film (De Azeredo 2009). Among the extracts of various herbs, Peganum Harmala seed extract is one of the compounds with significant antimicrobial effect (Ghorbanpour and Jahedi, 1394). Peganum Harmala extract contains flavonoids and alkaloids antimicrobial agents (Diba et al., 2009). Among different extraction methods, ultrasound assisted extraction is a cheap, simple and effective method. Increasing the extraction efficiency and speed are the main important advantages of this extraction method (Chemat et al., 2012). Moreover, less temperature is required for extraction, in which causes less damage to heat-sensitive compounds. The aim of this study was to prepare carrageenan/nanoclay/glycerol films containing Peganum Harmala extracts prepared with ultrasound assisted extraction and investigating the physical, mechanical and antimicrobial properties of the film. For the preparation of extracts, 10 g of dried Peganum Harmala seed was weighed and blended with 90 ml ethanol. The solution was sonicated at 400 W for 10 min (7 seconds on and 3 seconds off) at room temperature, using an ultrasonic probe. An ice bath was used to prevent evaporation of the solvent. After the sonication, the extraction was filtered with a filter paper and stored at 4°C in dark glass vials for further use. Carrageenan based films were fabricated by the solution casting method. Firstly, 3 w/w% of nanoclay (based on Carrageenan dry weight) was added to 100 ml deionized water and vigorously stirred for 24 h at ambient temperature. Then, the nanoclay solution was sonicated using 100 W ultrasonic probes (7 seconds on and 3 seconds off) for 10 min. Then, 2 g carrageenan was added to the nanoclay dispersions and stirred at 82°C for 20 min. Finally, 1, 2 and 3 v/v% (based on solution volume) of the extract were incorporated into the film forming solution and stirred until a homogeneous mixture was obtained. The final mixture was cooled down to 65°C and 30 ml of film solution was cast onto polystyrene Petri dishes with 8 cm in diameter. All film samples were dried in an oven at 25 °C for 24 h. Eventually, the dried films were stored in plastic bags before conducting the tests. Then, the effect of incorporation of the extract on the carrageenan film morphology, thermal stability, mechanical, optical, barrier and antibacterial properties were investigated. The purpose of this study was to prepare carrageenan biopolymer-based antimicrobial films for active food packaging and environmental pollution reduction caused by synthetic packaging material accumulation. Carrageenan nanocomposite films containing 3% nanoclay (montmorillonite), glycerol and three concentrations of 1, 2 and 3% of the Peganum Harmala extract were prepared by casting method and their physical, mechanical and antimicrobial properties were investigated against E. coli and S. aureus bacteria. To investigate the variations
resulting from adding Peganum Harmala extract to carrageenan/nanoclay nanocomposite films, scanning electron microscopy, thermogravimetric analysis, UV-Vis spectroscopy, FT-IR analysis were performed along the Fourier transformation of the films. The scanning electron microscope images from carrageenan/glycerol/nanoclay films with and without extracts showed a surface containing nanoclay, which were dispersed throughout the film. UV-Vis spectrometry showed that ultraviolet light and visible light of carrageenan/nanoclay/glycerol film was reduced by adding Peganum Harmala extract. This reduction in the sample containing 3% extract under ultraviolet light has been 2.6 - 0.3% and that of the visible light was 17.7- 9.2%. According to a thermogravimetric analysis, adding Peganum Harmala extract to carrageenan film did not have any obvious effect on the thermal stability of the film. Tensile strength and lengthening of carrageenan/nanoclay/glycerol film without extract were 15.9 MPa and 15.0 mm. The results of the tensile test showed that the Peganum Harmala extract in a polymer-based carrageenan/nanoclay/glycerol film increased tensile strength by 2 times and lengthening 3 times greater than carrageenan/nanoclay/glycerol film without the extract. Finally, according to antimicrobial tests, the Peganum Harmala extract is antimicrobial materials suitable for producing films and biodegradable coatings for different food packaging. The UV-Vis spectroscopy showed that the addition of the Peganum Harmala extract to the carrageenan/nanoclay/glycerol film reduced its ultraviolet and visible light transmission. Based on thermogravimetric analysis, the addition of extract to carrageenan films did not have any significant effect on the thermal stability of the film, but the binding between the functional groups of component of extract, glycerol and carrageenan polymer increased the thermal degradation temperature of the Glycerol. The results of the tensile test indicate that the presence of extracts in the carrageenan film increases its tensile strength compared to the extract-free carrageenan film. According to antibacterial test results, the films containing the extract had antimicrobial activity. By increasing the extract content, the antibacterial activity of film increased.