L. Hilliou

Characterization of an extracellular polysaccharide produced by a Pseudomonas strain grown on glycerol.

A new extracellular charged polysaccharide composed mainly by galactose, with lower amounts of mannose, glucose and rhamnose, was produced by the cultivation of Pseudomonas oleovorans NRRL B-14682 using glycerol as the sole carbon source. Thermal and solid-state NMR analysis showed that this polymer is essentially amorphous, with a glass transition temperature of 155.7 degrees C. The exopolysaccharide aqueous solutions have viscoelastic properties similar to that of Guar gum, but with affinity to salts as a result of its polyelectrolyte character. In addition, the exopolysaccharide has demonstrated good flocculating and emulsifying properties and film-forming capacity. These properties make this polymer a good alternative to more expensive natural polysaccharides, such as Guar gum, in several applications in the food, pharmaceutical, cosmetic, textile, paper and petroleum industries.

Nanobiocomposites of carrageenan, zein, and mica of interest in food packaging and coating applications.

The present study presents the development and characterization of biocomposites of a red-algae-derived carrageenan, mica, and their blends with zein prolamine obtained by solvent casting. The morphology of the blends was characterized by scanning and transmission electron microscopy (SEM and TEM), optical microscopy, and atomic force microscopy (AFM). Mechanical behavior, water barrier, water uptake, and UV-vis protection of the cast films were also investigated. The results indicated that the addition of 10 wt % glycerol to the blends resulted in a better dispersion of the additive and, for that reason, a better improvement for the studied properties. The composites were seen colored but transparent and exhibited the ability to block the UV-vis radiation because of the characteristic absorbing properties of the filler. Nevertheless, the main conclusion from the work is that the nanocomposites were seen to act as a reinforcing plasticizer and also led to significantly reduced water permeability and uptake. The clay was found to be more efficient in the latter aspect than the zein prolamine as an additive. As a result, these novel carragenan-based biocomposites can have significant potential to develop packaging films and coatings for shelf-life extension of food products.

Morphology and Water Barrier Properties of Nanobiocomposites of κ/ι-Hybrid Carrageenan and Cellulose Nanowhiskers

The current study presents the development and characterization of novel carrageenan nanobiocomposites showing enhanced water barrier due to incorporation of cellulose nanowhiskers (CNW). CNW, prepared by acid hydrolysis of highly purified α cellulose microfibers, were seen to have a length of around 25-50 nm and a cross section of ca. 5 nm when dispersed in the matrix. The nanobiocomposites were prepared by incorporating 1, 3, and 5 wt % of the CNW into a carrageenan matrix using a solution casting method. Morphological data (TEM and optical microscopy) of the nanocomposites containing CNW were compared with the morphology of the corresponding biocomposites containing the original cellulose microfibers and the differences discussed. Thermal stability by TGA, water vapor permeability, and percent water uptake were also determined. The main conclusion arising from the analysis of the results is that the nanobiocomposites containing 3 wt % of CNW exhibited the lowest reduction in water vapor permeability, that is, ca. 71%, and that this reduction was largely attributed to a filler-induced water solubility reduction. This fully biobased nanoreinforced carrageenan can open new opportunities for the application of this biopolymer in food-packaging and -coating applications.

Biodegradable Agar Extracted from Gracilaria Vermiculophylla: Film Properties and Application to Edible Coating

Gracilaria is a red algal genus that biosynthesizes a polymer called agar that is extensively used in the food and pharmaceutical industries as gelling and stabilizing agent. In the last years, many studies have focused on gel properties of this biopolymer; but the agar films and coatings still have few studies reported. The edible film and coating have a protective function, preventing moisture, oxygen and flavour transfers between food and surroundings. The objectives of this work are the production of biodegradable agar films from Gracilaria vermiculophylla, collected in Ria de Aveiro, Portugal, and the study of the effect of glycerol, an hydrophilic plasticizer, on the properties of the films and on subsequent application in edible coating of fresh fruits and vegetables. The agar extraction was carried out at specific optimum parameters determined in previous work (3.5 h pre-treatment duration, 6% NaOH concentration and 2 h extraction time). Agar films were made using the knife coating technique and compared with commercial agar. The physical properties of films such as hygroscopicity, mechanical resistance (Young’s modulus, tensile strength and elongation), and permeability to water vapour and oxygen were characterized. As expected, the plasticizer addition revealed and increase on elongation and decrease on tensile strength. The films were transparent and optically clear, showing good properties similar to the commercial agar films. The potential application of the agar/glycerol solution to fresh vegetable preservation was tested. Model fruits and vegetables were coated with the biopolymer/plasticizer solution and compared with a control sample in terms of colour, firmness, weight loss and shelf life. Considering on one hand the abundance of the raw algal material which is actually an invasive species, and the properties of the agar films and coatings obtained on the other hand, commercial use of G.vermiculophylla from Ria de Aveiro is well justified.

Postharvest culture in the dark: an eco-friendly alternative to alkali treatment for enhancing the gel quality of κ/ι-hybrid carrageenan from Chondrus crispus (Gigartinales, Rhodophyta).

After harvesting from natural stocks, female gametophytes of the red seaweed Chondrus crispus were cultured for several days under a light-deprived regime in order to determine if dark treatment can improve the gel quality of carrageenan extracted from the seaweed. An increase in the gel strength of native carrageenan was observed after dark treatment for 10d, but not after 5d, as compared to that of freshly harvested (baseline) seaweed. Corresponding decrease in sulfate and increase in 3,6-anhydrogalactose (3,6-AG) contents of the carrageenan extract were also observed. We posit that during dark treatment, the production of sulfated carrageenan precursor units was prevented while the enzymatic conversion of the prevailing precursor units to the gelation-promoting 3,6-AG was allowed to proceed. The observed increase in carrageenan gel strength with a 10-d dark treatment was comparable to the effect of the widely-used industrial procedure of alkali treatment in improving the extracts gel quality. Hence, postharvest culture in the dark for 10d can be an eco-friendly alternative to alkali treatment.

Rheological characterization of commercial highly viscous alginate solutions in shear and extensional flows

The rheological properties of sodium alginate in salt-free solutions were studied by steady shear, dynamic oscillatory and extensional measurements. This biopolymer consists of mannuronic and guluronic acid residues that give a polyelectrolyte character. We applied the scaling theories and checked their accordance with polyelectrolyte behaviour for low concentrations with a shift to neutral polymer behaviour at larger concentrations. This nature was supported by the effect of the concentration on the specific viscosity, the relaxation times from steady shear and the longest relaxation times from small amplitude oscillatory shear (SAOS) measurements. To analyze the extensional behaviour of the samples, we conducted a study of dimensionless numbers and time scales where filament thinning driven by viscous, capillary or elastic forces is at play. We conclude that an exponential filament thinning followed by breakup results in the best regimes that describe the experimental data. Besides, the data pointed out that alginate in salt-free concentrated solutions shows strain thinning of the extensional viscosity and chain rigidity, behaviours that cannot be inferred from the shear rheometry.

Drying kinetics of biofilms obtained from chestnut starch and carrageenan with and without glycerol

Drying kinetics of biofilms from chestnut starch and hybrid carrageenan were experimentally determined and modelled. The biofilms were obtained by mixing the respective solutions (4.0% w/w) of both substances in the proportion 80/20 of chestnut starch/hybrid carrageenan. Glycerol (at 5.0% w/w) was added to some biofilms. Biofilms were prepared using a casting method. Drying kinetics were performed at 30, 40, and 50°C for forced air convection (1.8 ± 0.1 m/s) and 30 and 50°C for natural convection. Constant drying rate period, above critical moisture content (5.4 and 4.2 kg water/kg d.b. without and with glycerol, respectively) allowed the evaluation of the heat transfer coefficients. The water diffusion coefficients were determined in the falling rate period assuming a semi-infinite slab with variable thickness. Water sorption isotherms of biofilms at 25°C were determined and fitted with the GAB model. Mechanical properties of different biofilms showed no significant differences for Youngs modulus values (44.0 ± 4.6 MPa). Nevertheless, films prepared at 30°C under natural drying showed the lowest values of tensile strength and elongation (32.2 ± 4.9 MPa and 0.85 ± 0.11%).

Thermo-compression molding of chitosan with a deep eutectic mixture for biofilms development

A eutectic mixture of choline chloride (ChCl) and citric acid (CA) was successfully used for the preparation of chitosan (Chit) bio-films by thermo-compression molding. Optimization of the film preparation conditions was carried out using response surface methodology and a Box-Behnken design based on the best mechanical properties and lowest energetic requirements (lower compression load and time). The optimum film, made with chitosan and ChCl–CA (eutectic mixture), was compared with films prepared using only CA in their formulation. Chit–ChCl–CA films presented higher elasticity, opacity and total color difference, and a lower tensile strength in relation to the Chit–CA films. Films prepared with the eutectic mixture presented higher water vapor permeability values. These results were associated with the films microstructures. FTIR analysis confirms the occurrence of chemical changes in the processed films. The thermo-compression process significantly affects the crystallinity of the pristine chitosan. The films thermal stability is depressed when compared to the stability of each component.

Hybrid carrageenans : isolation, chemical structure, and gel properties

Hybrid carrageenan is a special class of carrageenan with niche application in food industry. This polysaccharide is extracted from specific species of seaweeds belonging to the Gigartinales order. This chapter focuses on hybrid carrageenan showing the ability to form gels in water, which is known in the food industry as weak kappa or kappa-2 carrageenan. After introducing the general chemical structure defining hybrid carrageenan, the isolation of the polysaccharide will be discussed focusing on the interplay between seaweed species, extraction parameters, and the hybrid carrageenan chemistry. Then, the rheological experiments used to determine the small and large deformation behavior of gels will be detailed before reviewing the relationships between gel properties and hybrid carrageenan chemistry.

Assessing the practical utility of the hole-pressure method for the in-line rheological characterization of polymer melts

The most promising method capable of providing accurate measurements of the first and second normal-stress differences in shear flows at shear rates typical of polymer processing is the so-called hole-pressure method, but its use has not been as widespread as would be expected, namely due to the experimental difficulties associated with performing such experiments accurately. In this work, we use a small-scale modular slit die to assess the practical utility of the method for in-line monitoring of polymer melt flow. We provide a quantitative analysis of intrinsic error sources and use state-of-the-art data acquisition tools to minimize errors associated with pressure transducers. Our results demonstrate that the method can be used to accurately measure the viscosity and first normal-stress difference in melts but probably not the second normal-stress difference because the intrinsic errors are too high, even when the influence of all the potential error sources is minimized or eliminated.