Search

In this work, the film-forming capacity of the new microbial exopolysaccharide (EPS) composed by sugars and acyl groups, produced by Pseudomonas oleovorans NRRL B-14682, was studied. The films were transparent and quite flexible and tough when handled, but showed to be stiff under tensile and puncture tests. They presented a high water vapour permeability but a quite low permeability to carbon dioxide, which are typical of hydrophilic polysaccharide films. Furthermore, they showed good stability in contact with liquid water, after auto-crosslinking reactions at low pH, upon or after drying. Preliminary biodegradability tests indicated an easy biological degradation when exposed to soil microorganisms. The results obtained are rather promising regarding the film-forming capacity of the new EPS, as they were obtained only with the biopolymer itself. The films formulation may be complemented with additives (e.g. plasticizers, emulsifiers, nanocomposites), to design films for specific applications.

The effect of temperature on the dynamic and steady-shear rheology of aqueous solutions of an extracellular polysaccharide produced by microbial fermentation using Pseudomonas oleovorans NRRL B-14682 and glycerol byproduct, was studied. The biopolymer solutions have shown a pseudoplastic fluid behaviour and no gel formation was detected for all temperatures studied. As expected, the steady shear and dynamic parameters decreased with increasing temperature, due to the increase of polymer chain mobility. The EPS solutions were thermorheologically simple and stable, since the rheological parameters were successfully superimposed to and arbitrary reference temperature using the Time–Temperature Superposition principle, and the Cox-Merz rule was satisfactorily applied. In addition, the rheological properties were maintained under consecutive oscillatory and steady-state tests at 25 °C, after exposing the sample to increasing temperatures up to 80 °C. This polymer is a good candidate to be used in industrial processes involving temperature variations, at least in the range from 15 to 80 °C.

In this work, the enhancement of the barrier properties to water vapour and gases (CO2 and O2) of a polymeric matrix composed by kappa-carrageenan and pectin (66.7% kappa-carrageenan), with the inclusion of mica flakes, was studied. The effect of the films mica content on the water vapour permeability (WVP) was dependent on the driving force applied. A higher WVP reduction (of about 40% for a mica content of 10%, mass of mica per mass of dry polymer), was observed when the films were more homogenously hydrated throughout their thickness. A significant decrease was also observed for both CO2 and O2 permeabilities (73% and 27%, respectively), in conditions where the films were plasticized with water (25% of water, dry basis), for which there is a depletion of the good barrier properties characteristic of dry polysaccharide films. In addition, the composition of 10% of mica flakes in the polymer matrix represented a critical volume fraction of inorganic particles, above which there was a decrease of the films barrier properties, for all components tested.

We report the solution properties of a new exopolysaccharide (EPS) obtained from a Pseudomonas strain fed with glycerol as the sole source of carbon. This high molecular mass (3 × 10 6 g mol −1 ) biopolymer is essentially made of galactose monomers with pyruvate and succinate groups imparting a polyelectrolyte character. The Smidsrod parameter B computed from the ionic strength dependence of the intrinsic viscosity indicates that the EPS backbone is rather flexible. In salt free aqueous solutions, the zero shear viscosity scaling with concentration follows a typical polyelectrolyte behavior in bad solvent, whereas at high ionic strength the rheological response is reminiscent from neutral polymers. Light scattering data indicate that the EPS adopts a globular conformation as a result of hydrophobic interactions. EPS solutions are stable within 4 days as particle sizing does not indicate EPS aggregation. Both globular conformation and stability against precipitation from solution are attributed to the low charge density of the polyelectrolyte.

The functional properties of a novel extracellular polysaccharide (EPS) produced by Pseudomonas oleovorans grown on glycerol byproduct, generated by the biodiesel industry, were investigated. The EPS is a high molecular weight (4.6 × 10 6 ) heteropolysaccharide, composed by neutral sugars (galactose, 68%; mannose, 17%; glucose, 13%; rhamnose, 2%; fucose, 4%) and acyl groups (3.04%). This biopolymer has pseudoplastic fluid behaviour in aqueous media. The apparent viscosity was stable for the pH range 2.9–7.1 and NaCl concentrations up to 1.0 M. Though the apparent viscosity decreased at high temperatures, at alkaline conditions and at NaCl concentrations of 2.0 M, pseudoplastic fluid behaviour was retained. The EPS was capable of stabilizing water emulsions with several hydrophobic compounds, including hydrocarbons, vegetable and mineral oils. It retained its emulsifying activity during exposure to wide temperature (30–50 °C) and pH (2–12) variations, as well as to the presence of NaCl at concentrations as high as 2.0 M.

Bilayer films of FucoPol and chitosan were prepared and characterized in terms of optical, morphologic, hygroscopic, mechanical and barrier properties, to evaluate their potential application in food packaging. Bilayer films have shown dense and homogeneous layers, and presented enhanced properties when comparing to monolayer FucoPol films. Though, a high swelling degree in contact with liquid water (263.3%) and a high water vapour permeability (0.75 × 10 −11 mol/ms Pa), typical of polysaccharide films, was still observed. However, they presented a low permeability to O 2 and CO 2 (0.47 × 10 −16 mol m/m 2 s Pa and 5.8 × 10 −16 mol m/m 2 s Pa, respectively). Tensile tests revealed a flexible and resistant film with an elongation at break of 38% and an elastic modulus of 137 MPa. The studied properties, in particular the excellent barrier to gases, impart these bilayer films potential to be used in packaging of low moisture content products, as well as in multilayered hydrophobic/hydrophilic/hydrophobic barriers for food products with a broader range of water content.

Enterobacter sp. was grown on glycerol byproduct from the biodiesel industry for the production of a value-added exopolysaccharide (EPS). The culture broth was characterized in terms of its morphological and rheological properties throughout the cultivation run. Microscopic observations revealed the formation of cell aggregates surrounded by the EPS at the beginning of the cultivation run, while, at the end, aggregates were reduced and an EPS matrix with the cells embedded in it was observed. The apparent viscosity of the culture broth increased over time, which was attributed to the increase of the EPS concentration in the first period of the cultivation run. However, in the final stage, the creation of new polymer interactions within the complex culture broth was likely the reason for the viscosity increase observed, since there was not a significant variation of the EPS concentration, average molecular weight or chemical composition. The broth presented a Newtonian behavior at the beginning of the run, changing to pseudoplastic as the EPS concentration increased, and revealed to follow the Cox–Merz rule.

This work explores the novelty of dissolving chitin-glucan complex (CGC), from two fungal strains, Komagataella pastoris (CGCP) and Aspergillus niger (CGCKZ) (KiOnutrime-CG™), using biocompatible ionic liquids (ILs). Three cholinium-based ILs were tested, choline acetate, choline propionate and choline hexanoate. Although all tested ILs resulted in the dissolution of the co-polymer at a concentration of 5 % (w/w), distinct polymeric structures, films or gels, were obtained from CGCP and CGCKZ, respectively. CGCP films were dense, flexible and elastic, with high swelling capacity (> 200 %). The IL anion alkyl chain length influenced the polymeric structures’ properties, namely, the CGCP films elongation at break and swelling degree. CGCKZ resulted in weak gels. For both polymeric structures, exposure to the ILs under the dissolution conditions caused significant changes in the co-polymers’ chemical structure, namely, reduction of their glucan moiety and reduction of the degree of acetylation, thus yielding chitosan-glucan complexes (ChGC) enriched in glucosamine (53.4 ± 0.3–60.8 ± 0.3 %) info:eu-repo/semantics/publishedVersion