Comparative Evaluation of Physical Properties of Edible Chitosan Films Prepared by Different Drying Methods

Edible films are alternative packaging, which have recently received much attention due mainly to environmental reasons. Edible films may be formed from edible biomaterials such as polysaccharides, proteins, or lipids. Among these biopolymers, chitosan is of interest because it has a good film-forming property and is biodegradable, biocompatible, and nontoxic. Several techniques have been used to prepare edible chitosan films with various degrees of success. However, it is always interesting to find an alternative technique to produce films of superior quality at shorter processing (drying) time. In this study, the influences of different drying methods and conditions on the drying kinetics and various properties of chitosan films were investigated. Drying at control conditions (ambient air drying and hot air drying at 40°C) as well as vacuum drying and low-pressure superheated steam drying (LPSSD) at an absolute pressure of 10 kPa were carried out at different drying temperatures (70, 80, and 90°C). The properties of chitosan films, in terms of color, tensile strength, percent elongation, water vapor permeability (WVP), glass transition temperature (T_g), and crystallinity, were also determined. Based on the results of both the drying behavior and film properties, LPSSD at 70°C was proposed as the most favorable conditions for drying chitosan films.     

Formation and stability of multiple-layered liposomes by layer-by-layer electrostatic deposition of biopolymers

The sequential deposition of biopolymers onto the surface of liposomes; lamellar bilayer vesicles composed of polar lipids; was investigated. Submicron-sized liposomes were prepared from lecithin with a high speed blender and an ultrasonic homogenizer. Positively (chitosan), and negatively (high methoxyl pectin and λ-carrageenan) charged biopolymers were alternatingly added to liposomes to build up to 6 sequentially-stacked interfacial layers on top of the phospholipid membranes. After formulation, particle size and ζ-potential of liposomes were determined using dynamic light scattering. The primary liposomes had diameters of approximately 80 nm. Particle size increased linearly with each successive deposition up to four layers but increased to several micrometers when a fifth and sixth layer was deposited indicating that aggregation may have occurred. Addition of λ-carrageenan as an anionic biopolymer led to less aggregation than when high methoxyl pectin was used. Results were attributed to (i) unbound polymers in the aqueous phase forming coacervates that may lead to depletion flocculation and (ii) unoccupied binding sites and uneven charge distributions causing bridging flocculation. Our results show the limitations of the layer-by-layer deposition approach, which is important for food manufacturers wishing to form very thick polymer layers to stabilize dispersions such as emulsions or liposomes.     

Formation and characterization of lactoferrin/pectin electrostatic complexes: Impact of composition,pH and thermal treatment

Protein–polysaccharide complexes may be used for the development of delivery systems with applications in several industries. In the present work, the interaction of lactoferrin (LF, 0.2wt%) with a High-Methoxyl pectin (0.005–0.15wt%) in aqueous solutions was studied at different pH values (2–7) and temperatures (30–90 °C) at low ionic strength. ζ-potential and light-scattering techniques were used to provide information about the electrical charge and aggregation of individual biopolymers and complexes. At pH 7, the electrical charge went from positive to negative when increasing amounts of pectin were added to the LF solution, which was attributed to the formation of an electrostatic complex. These complexes remained soluble (low turbidity) from pH 7 to 3.5, but became turbid between pH 3.5 and 2, due to charge neutralization and bridging effects. At pH 7, the stability of LF–pectin complexes to aggregation during heating was much better than LF alone. The results of this study should provide information that will facilitate the utilization of lactoferrin as a bioactive component in food systems.     

Optimization of the biocide properties of chitosan for its application in the design of active films of interest in the food area

The influence on biocide performance of some unprecedented physicochemical features of chitosan cast films such as film thickness, pH of the nutrient broth, film neutralization, film autoclave sterilization and temperature exposure were analyzed against Staphylococcus aureus and in some experiments also against Salmonella spp. The work demonstrates for the first time the influence of the release or positive migration of protonated glucosamine fractions from the biopolymer into the microbial culture as the responsible event for the antimicrobial performance of the biopolymer under the studied conditions. From the results, a reliable and reproducible method for the determination of the bactericidal activity of chitosan-based films was developed in an attempt to standardize the testing conditions for the optimum design of active antimicrobial food packaging films and coating applications.     

Surface Morphology and Dissolution Rate of Slow Discharge Urea Coated with Starch-Urea-Borax Matrix

Pure starches do not exhibit fast tacking and high viscosity to meet the standards set by many industrial processes. Therefore, the objective of this work was to obtain high- viscosity coating solutions after modifying tapioca starch with urea as a cross-linker and borax as a thickener. Study of the physical properties confirmed that the prepared solutions were exhibiting more pronounced non-Newtonian behavior. A shear-thinning behavior followed by shear-thickening was observed for all solution compositions. At room temperature, the critical shear rate at which the transition from shear-thinning to shear-thickening occurred was ranging from 45.8 to 78 s^?1. However, the shear-thickening response to the applied shear rate was less prominent at higher temperatures. The surface tension and density of the solutions were found to decrease monotonically with an increase in temperature. Once the physical properties were fully understood, 1, 1.5 and 2 mL of each solution were used to coat 30 g of urea fluidized above its minimum level of fluidization. The phenomenological analyses of the coated and uncoated urea samples were carried out by understating their surface morphology, coating thickness, percent coating, dissolution rate, percent release and crushing strength. It was concluded that the coating thickness, percent coating, dissolution rate and percent release increase over time with an increase in solution volume and borax mass; however, some random results were obtained while investigating the effects of the solution volume on the crushing strength. The highest crushing strength was noticed for urea samples coated with 1.5 mL of solution followed by 1 mL, 2 mL and without coating.     

Structure and properties of nanocomposite films based on sodium caseinate and nanocellulose fibers

Films made from sodium caseinate and nanocellulose were prepared by dispersing the fibrils into film forming solutions, casting and drying. Composite films were less transparent and had a more hydrophilic surface than neat sodium caseinate ones. However, the global moisture uptake was almost not affected by filler concentration. Addition of nanocellulose to the neat sodium caseinate films produced an initial increase in the barrier properties to water vapor, and then, it decreases as filler content increased. This was explained in terms of additional detrimental changes (cracks and bubble formation) induced in the morphological structure of the film by the reinforcement.The tensile modulus and strength of composite films increased significantly with increasing cellulose concentrations, while the values of elongation decreased. In the same way it was found that the storage modulus increases considerably with filler addition in the low temperature range (<60 °C), though the effect of temperature on the films performance is even more dramatic, as expected in protein-based materials.     

Filament stretchability of biopolymer fluids and controlling factors

Filament stretchability of biopolymer fluids composed of casein and waxy maize starch has been investigated as a function of fluid properties (viscosity and viscoelasticity) and stretching speed. The stretching of a filament was conducted at a controlled speed using a Texture Analyzer and was monitored using a high speed camera. The maximum stretchable length, L_max, was used to quantify the stretchability of a filament. Influences of various contributing factors were analyzed using dimensionless numbers (Ohnesorge number Oh, Weber number We, and capillary number Ca). It was found that, for fluids that are dominantly viscous, the capillary number could be the dominant factor determining filament stretching, demonstrated by the master curve of the maximum stretchable length against the capillary number. However, for increasingly viscoelastic fluids, the stretching behaviour showed significant deviation from the master curve, suggesting that viscoelasticity could be another pronounced factor influencing the stretching of such biopolymer fluids.     

Anomalous Viscosity Behavior in Aqueous Solutions of Hyaluronic Acid

Summary Effects of steady shear flows on intermolecular interactions in dilute and semidilute aqueous solutions of hyaluronic acid (HA) are reported. Pronounced shear thinning behavior is observed for solutions of HA at high shear rates, and no hysteresis effects are detected upon the subsequent return to low shear rates. With the aid of the asymmetric flow field-flow fractionation (AFFFF) technique, it is shown that mechanical degradation of the polymer does not take place in these shear viscosity experiments, even at high shear rates. The low shear rate viscosity of a semidilute HA solution decreases by approximately 40% when the temperature is increased from 10 °C to 45 °C. It is shown that when a dilute HA solution is exposed to a low fixed shear rate (0.001 s^-1), a marked viscosification occurs in the course of time and prominent intermolecular complexes are formed. It is argued that shear-induced alignment and stretching of polymer chains promote the evolution of hydrogen-bonded structures, where cooperative zipping of stretched chains generates a network. At a higher constant shear rate (0.1 s^-1), the viscosity decreases as time goes because of the alignment of the polymer chains, but the higher shear flow perturbation prevents the chains in dilute solutions from building up association complexes. The viscosity of an entangled HA solution is not changed in the considered time window at this shear rate, but the network structures breakdown at the highest shear rate (1000 s^-1), and then they are restored upon return to a low shear rate.     

Physical properties of cassava starch–carnauba wax emulsion films as affected by component proportions

Properties of glycerol‐plasticised cassava starch–carnauba wax emulsion films were studied as functions of carnauba wax/starch (CW/S) ratios. Increases in CW concentrations improved elongation, but impaired tensile strength and elastic modulus, suggesting a plasticising effect by CW and/or the emulsifier. CW reduced water solubility of the films and decreased their water vapour permeability (WVP) up to CW/S ratios of 0.15–0.20, probably because of the decreased water solubility. Higher CW concentrations resulted in increased WVP, possibly due to starch matrix loosening. The opacity imparted by high CW concentrations in films could compromise some applications. The T_g of starch and the expected CW effects on it were not evidenced by DSC thermograms, but CW seems to have affected starch crystallisation, maybe by forming complexes with amylose and/or amylopectin.