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.     

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.     

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.     

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.     

Immobilization of ZnO on Chitosan-Neem seed composite for enhanced thermal and antibacterial activity

Natural and inorganic materials of Chitosan-Zinc oxide-Neem seed (CS-ZnO-NS) hybrid composite were synthesized by chemical precipitation method. The obtained CS-ZnO-NS hybrid composites were characterized for functional group confirmation by Fourier transform infrared spectroscopy and UV–Visible spectroscopy. The ZnO particles connected to biopolymers exhibited small grains and rod, bullet like structure confirmed by scanning electron microscopy and transmission electron microscopy analysis. The size of the prepared CS-ZnO-NS hybrid composite was found to be 20–80?nm. The crystalline behaviors were determined by X-ray diffraction analysis. The surface area of the prepared hybrid composite was determined using BET analysis. The elemental composition was analyzed by energy dispersive X-ray spectroscopy and thermal behaviors by thermo gravimetric analysis. The obtained result shows that zinc oxide was well able to incorporate into chitosan-neem seed composite which enhances the thermal stability. Further, the antibacterial activity evaluated by agar well diffusion method against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli bacteria exhibits higher inhibition effect because of ZnO particles presence in the chitosan-neem seed. Hence the CS-ZnO-NS is a promising material for biomedical applications.