Fabrication And Characterization Of Bio-nanocomposite Edible Films Based On Tara Gum Reinforced With Chitosan Nanoparticles

The need for replacing conventional synthetic packaging with biodegradable polymers from biological origin in order to decrease waste through biological recycling has created an increasing demand for new materials with film forming abilities. The aim of this study was to use tara gum as a novel material for the production of edible films suitable for active packaging applications reinforced with chitosan nanoparticles.In the first phase of the study, tara gum was optimized as edible film material and the influence of polyols as plasticizers on the physicochemical properties of the films was evaluated. Thermomechanical, physicochemical and barrier properties were determined as a function of plasticizer type and concentration. Three polyols with different molecular mass and number of oxygen atoms (glycerol, sorbitol and PEG400) were used as plasticizers in the range of0.075-0.3g/tara gum g. Tensile strength and elongation at break decreased with the increasing molecular mass and number of oxygen atoms of the plasticizer. Characterization of the plasticized films showed that glycerol was the best plasticizer in terms of mechanical properties with the highest elongation (16-44%) and resistance (>45MPa) and sorbitol presented the best barrier properties by exhibiting the lowest hydrophilicity and water vapor permeability (0.24-0.34g mm m-2h-1kPa-1). PEG400on the other hand had no plasticizing effect on the polymer and diminished all its properties. Fourier transform infrared (FTIR) spectroscopy showed no significant effect on the structure of the polysaccharide. Dynamic mechanical analysis (DMA) revealed that incorporation of plasticizers increased the mobility of the system by decreasing the intermolecular forces between the polymer chains and therefore reduced both glass transition and melting temperature. Glycerol and PEG400had the biggest effect on the glass transition and melting temperature reducing it by30℃and100℃respectively.In the second phase of this study, we describe the conditions to optimize chitosan-tripolyphosphate nanoparticles as potential nano-fillers in edible films production. The size of chitosan-tripolyphosphate particles depends highly on ionic cross-linking between the cationic amino groups on the chitosan (CS) chain and the anionic phosphate groups of sodium tripolyphosphate (TPP). Ionic cross-links are affected by the relative concentrations of CS and TPP, ionic strength, pH. Particle size, polydispersity index (PDI) and surface ξ-potential were controlled by chitosan’s Mw and concentration. Post-processing methods such as centrifugation and ultra-sonication were used to further control particle size. We show that particle size can be controlled by selecting appropriate conditions. Particles with sizes below120nm were produced at different CS:TPP mass ratios depending on the CS concentration. Dilute NaCl was the optimal solution ionic composition that decreased the size by25%and also resulted in a narrow particle size distribution. We show using UV-vis spectrophotometry that particles of different size, separated by centrifugation, had different phosphorus content. Ultra-sonication can be used to reduce the size by50%but long time caused fragmentation of the nanoparticles. Transmission electron microscopy (TEM) revealed the differences in the morphology of chitosan nanoparticles under various fabrication conditions.During the fabrication of chitosan-tripolyphosphate nanoparticles, there was formation of sodium acetate during (NaOAc) in the solution as a result of the reaction between the acetic acid used for the dissolution of chitosan and sodium hydroxide used for adjusting the pH of the chitosan solution. For that reason, the effect of sodium acetate on the mechanical and physicochemical properties of tara gum films was examined. The results reveal that incorporation of NaOAc into the TG films diminished all of its physicochemical properties except elongation. Addition of20%NaOAc:TG decreased the TS by approximately80%while E%increased by93%. Additionally, with increasing NaOAc concentration the moisture content of tara gum films gradually increased up to13.19%due to its hydrophilic and hygroscopic nature. This attraction of water in the structure of the film weakened the intermolecular forces between the chains of adjacent macromolecules allowing the water molecules to permeate through the polymer matrix of TG and consequently increase water solubility and water vapor permeability. These results show that incorporation of NaOAc had very similar plasticizing effects with glycerol when introduced in the polymer matrix. However, NaOAc diminished the tensile strength of the film more compared to glycerol.Finally, tara gum films were successfully produced with the inclusion of bulk chitosan or chitosan nanoparticles at various concentrations. The composites films were compared in terms of antimicrobial activity, thermomechanical, physicochemical and barrier properties. The thermal stability of the films was studied using thermogravimetric analysis (TGA). Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) measurements were used to study the interactions and compatibility between the polysaccharides within the films. The microstructure of the films was analyzed using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Incorporation of chitosan nanoparticles improved mechanical, physicochemical and barrier properties. Tensile strength was increased by35.73MPa while the elongation was decreased by7.21%. Water solubility and water vapor permeability (WVP) were reduced by74.3%and22.7%, respectively. The compact structure of the chitosan nanoparticles reduced the free volume of the polymer matrix more than bulk chitosan by obstructing the diffusion of water and thereby decreasing the moisture content of the films. Additionally, the microstructure of the films showed that the nanoparticles were distributed homogenously with in the structure and increased the roughness of the surface. However, tara gum films with bulk chitosan exhibited better antimicrobial activity. Incorporation of chitosan nanoparticles produced films less effective against Escherichia coli compared to Staphylococcus aureus, and their antimicrobial activity was reduced at high concentrations probably due to agglomeration.