Browsing by Author "Reis, Maria A.M."
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- Cation-mediated gelation of the fucose-rich polysaccharide FucoPol: preparation and characterization of hydrogel beads and their cytotoxicity assessmentPublication . Fialho, Letícia; Araújo, Diana; Delgado Alves, Vitor; Roma-Rodrigues, Catarina; Baptista, Pedro V.; Fernandes, Alexandra R.; Freitas, Filomena; Reis, Maria A.M.This study describes for the first time the iron- and copper-mediated gelation of FucoPol, fucoserich bacterial polysaccharide. The ability of FucoPol to gel in the presence of metal cations, including iron(III) and copper(II), was used for the preparation of hydrogel beads. Iron mediated the formation of stable and not cytotoxic gel beads, while copper resulted in fragile and cytotoxic ones. Copper-mediated beads coated with an iron-mediated gel layer were more stable and had reduced cytotoxicity. The resulting polymeric structures had differing morphology, physical properties and cytotoxicity, which support their use in several applications, including biomedicine, agriculture and bioremediation
- Characterisation of Films Based on Exopolysaccharides from Alteromonas Strains Isolated from French Polynesia Marine EnvironmentsPublication . Concórdio-Reis, Patrícia; Pereira, João R.; Delgado Alves, Vitor; Nabais, Ana R.; Neves, Luísa A.; Marques, Ana C.; Fortunato, Elvira; Moppert, Xavier; Guezennec, Jean; Reis, Maria A.M.; Freitas, FilomenaThis work assessed the film-forming capacity of exopolysaccharides (EPS) produced by six Alteromonas strains recently isolated from different marine environments in French Polynesia atolls. The films were transparent and resulted in small colour alterations when applied over a coloured surface (ΔEab below 12.6 in the five different colours tested). Moreover, scanning electron microscopy showed that the EPS films were dense and compact, with a smooth surface. High water vapour permeabilities were observed (2.7–6.1 × 10−11 mol m−1 s−1 Pa−1), which are characteristic of hydrophilic polysaccharide films. The films were also characterised in terms of barrier properties to oxygen and carbon dioxide. Interestingly, different behaviours in terms of their mechanical properties under tensile tests were observed: three of the EPS films were ductile with high elongation at break (ε) (35.6–47.0%), low tensile strength at break (Ꞇ) (4.55–11.7 MPa) and low Young’s modulus (εm) (10–93 MPa), whereas the other three were stiffer and more resistant with a higher Ꞇ (16.6–23.6 MPa), lower ε (2.80–5.58%), and higher εm (597–1100 MPa). These properties demonstrate the potential of Alteromonas sp. EPS films to be applied in different areas such as biomedicine, pharmaceuticals, or food packaging
- Characterization and biotechnological potential of extracellular polysaccharides synthesized by Alteromonas strains isolated from French Polynesia marine environmentsPublication . Concórdio-Reis, Patrícia; Delgado Alves, Vitor; Moppert, Xavier; Guezennec, Jean; Freitas, Filomena; Reis, Maria A.M.Marine environments comprise almost three quarters of Earth’s surface, representing the largest ecosystem of our planet. The vast ecological and metabolic diversity found in marine microorganisms suggest that these marine resources have a huge potential as sources of novel commercially appealing biomolecules, such as exopolysaccharides (EPS). Six Alteromonas strains from different marine environments in French Polynesia atolls were selected for EPS extraction. All the EPS were heteropolysaccharides composed of different monomers, including neutral monosaccharides (glucose, galactose, and mannose, rhamnose and fucose), and uronic acids (glucuronic acid and galacturonic acid), which accounted for up to 45.5 mol% of the EPS compositions. Non-carbohydrate substituents, such as acetyl (0.5–2.1 wt%), pyruvyl (0.2–4.9 wt%), succinyl (1–1.8 wt%), and sulfate (1.98–3.43 wt%); and few peptides (1.72–6.77 wt%) were also detected. Thermal analysis demonstrated that the EPS had a degradation temperature above 260 C, and high char yields (32–53%). Studies on EPS functional properties revealed that they produce viscous aqueous solutions with a shear thinning behavior and could form strong gels in two distinct ways: by the addition of Fe2+, or in the presence of Mg2+, Cu2+, or Ca2+ under alkaline conditions. Thus, these EPS could be versatile materials for different applications
- Exopolysaccharides enriched in rare suggars: bacterial sources, production and applicationsPublication . Roca, Christophe; Alves, Vitor D.; Freitas, Filomena; Reis, Maria A.M.Microbial extracellular polysaccharides (EPS), produced by a wide range of bacteria, are high molecular weight biopolymers, presenting an extreme diversity in terms of chemical structure and composition. They may be used in many applications, depending on their chemical and physical properties. A rather unexplored aspect is the presence of rare sugars in the composition of some EPS. Rare sugars, such as rhamnose or fucose, may provide EPS with additional biological properties compared to those composed of more common sugar monomers. This review gives a brief overview of these specific EPS and their producing bacteria. Cultivation conditions are summarized, demonstrating their impact on the EPS composition, together with downstream processing. Finally, their use in different areas, including cosmetics, food products, pharmaceuticals, and biomedical applications, are discussed
- Fucose-containing exopolysaccharide produced by the newly isolated Enterobacter strain A47 DSM 23139Publication . Freitas, Filomena; Alves, Vitor D.; Torres, Cristiana A.V.; Cruz, Madalena; Sousa, Isabel; Melo, Maria João; Ramos, Ana M.; Reis, Maria A.M.Enterobacter strain A47 (DSM 23139) was found to produce a fucose-containing exopolysaccharide (EPS). The EPS is composed of fucose, galactose, glucose, pyruvate, succinate and acetate in the molar ratios 1.6:1.3:1.1:1.2:0.7:1.5. It is a high molecular weight (5.8×106) homogeneous biopolymer, as indicated by the low polydispersity value (1.3). The steady shear flow properties of the EPS aqueous solutions are similar to guar gum and fucogel, and its viscoelastic properties indicate the formation of viscous aqueous solutions with entangled polymer chains. Additionally, the EPS has demonstrated good flocculating and emulsion stabilizing capacities, comparable to some commercially available products. These functional propertiesmakethe fucose-containing EPS a good alternative tomanysynthetic polymers, as well as other natural polysaccharides, in several applications in the food, pharmaceutical, cosmetic, textile, paper and petroleum industries.
- Kinetics of production and characterization of the fucose-containing exopolysaccharide from Enterobacter A47Publication . Torres, Cristiana A.V.; Marques, Rodolfo; Antunes, Sílvia; Alves, Vitor D.; Sousa, Isabel; Ramos, Ana Maria; Oliveira, Rui; Freitas, Filomena; Reis, Maria A.M.A fucose-containing exopolysaccharide (EPS) was produced by the bacterium Enterobacter A47 using glycerol byproduct from the biodiesel industry. The analysis of kinetic data suggested a partially growth associated EPS synthesis model. Although the EPS was composed of fucose, galactose and glucose at all cultivation stages, their relative proportion has varied considerably during the run. At the beginning (24 h), glucose was the main component (82.4 wt.%), being fucose and galactose minor components (5.0 wt.% and 10.9 wt.%, respectively), while at the end (96 h) it was composed of 26.0 wt.% fucose, 28.9 wt.% galactose and 43.7 wt.% glucose. The acyl groups content and composition have also changed, reaching their maximum content (19.2 wt.%) at the end of the run. Moreover, the molecular weight has increased linearly during the run (from 8 × 105 to 5 × 106). The changes observed in EPS composition and molecular weight have also had an impact upon the polymer’s intrinsic viscosity, as shown by its linear increase from 3.95 to 10.72 dL g−1. The results suggest that the culture might have synthesized at least two distinct EPS, with different sugar composition and average molecular weight, which predominated at different cultivation stages
- Low Temperature Dissolution of Yeast Chitin-Glucan Complex and Characterization of the Regenerated PolymerPublication . Araújo, Diana; Delgado Alves, Vitor; Marques, Ana C.; Fortunato, Elvira; Reis, Maria A.M.; Freitas, FilomenaChitin-glucan complex (CGC) is a copolymer composed of chitin and glucan moieties extracted from the cell-walls of several yeasts and fungi. Despite its proven valuable properties, that include antibacterial, antioxidant and anticancer activity, the utilization of CGC in many applications is hindered by its insolubility in water and most solvents. In this study, NaOH/urea solvent systems were used for the first time for solubilization of CGC extracted from the yeast Komagataella pastoris. Di erent NaOH/urea ratios (6:8, 8:4 and 11:4 (w/w), respectively) were used to obtain aqueous solutions using a freeze/thaw procedure. There was an overall solubilization of 63–68%, with the highest solubilization rate obtained for the highest tested urea concentration (8 wt%). The regenerated polymer, obtained by dialysis of the alkali solutions followed by lyophilization, formed porous macrostructures characterized by a chemical composition similar to that of the starting co-polymer, although the acetylation degree decreased from 61.3% to 33.9–50.6%, indicating that chitin was converted into chitosan, yielding chitosan-glucan complex (ChGC). Consistent with this, there was a reduction of the crystallinity index and thermal degradation temperature. Given these results, this study reports a simple and green procedure to solubilize CGC and obtain aqueous ChGC solutions that can be processed as novel biomaterials
- Low temperature dissolution of yeast chitin-glucan complex and characterization of the regenerated polymerPublication . Araújo, Diana; Delgado Alves, Vitor; Marques, Ana C.; Fortunato, Elvira; Reis, Maria A.M.; Freitas, FilomenaChitin-glucan complex (CGC) is a copolymer composed of chitin and glucan moieties extracted from the cell-walls of several yeasts and fungi. Despite its proven valuable properties, that include antibacterial, antioxidant and anticancer activity, the utilization of CGC in many applications is hindered by its insolubility in water and most solvents. In this study, NaOH/urea solvent systems were used for the first time for solubilization of CGC extracted from the yeast Komagataella pastoris. Di erent NaOH/urea ratios (6:8, 8:4 and 11:4 (w/w), respectively) were used to obtain aqueous solutions using a freeze/thaw procedure. There was an overall solubilization of 63–68%, with the highest solubilization rate obtained for the highest tested urea concentration (8 wt%). The regenerated polymer, obtained by dialysis of the alkali solutions followed by lyophilization, formed porous macrostructures characterized by a chemical composition similar to that of the starting co-polymer, although the acetylation degree decreased from 61.3% to 33.9–50.6%, indicating that chitin was converted into chitosan, yielding chitosan-glucan complex (ChGC). Consistent with this, there was a reduction of the crystallinity index and thermal degradation temperature. Given these results, this study reports a simple and green procedure to solubilize CGC and obtain aqueous ChGC solutions that can be processed as novel biomaterials
- Novel hydrogels based on yeast chitin-glucan complex: Characterization and safety assessmentPublication . Araújo, Diana; Delgado Alves, Vitor; Lima, Sofia A.C.; Reis, Salette; Freitas, Filomena; Reis, Maria A.M.Chitin-glucan complex (CGC) was used for the first time for the preparation of hydrogels. Alkali solvent systems, NaOH and KOH solutions, either at 1 or 5 mol/L, were used for CGC dissolution using a freeze-thaw procedure (freezing at −20 °C and thawing at room temperature; four cycles). The CGC solutions thus obtained were subjected to dialysis that induced the spontaneous gelation of the biopolymer, yielding translucid hydrogels with a yellowish coloration. Although all CGC hydrogels exhibited porous microstructures, high water content (above 97%) and good mechanical properties, their morphology, viscoelastic properties and texture were influenced by the type of solvent system used for CGC dissolution, as well as by their ionic strength. The K-based hydrogels presented a less compact network with larger pores and exhibited lower elastic properties. The Na-based hydrogels, on the other hand, exhibited a denser structure with smaller pores and a stiffer gel structure. These results show that it is possible to prepare CGC hydrogels with differing characteristics that can be suitable for different applications. Furthermore, all hydrogels were non-cytotoxic towards L929 fibroblasts and HaCaT keratinocytes. This study demonstrates CGC can be used to prepare biocompatible hydrogels with properties render them promising biomaterials
- Preparation and characterization of films based on a natural P(3HB)/mcl-PHA blend obtained through the co-culture of Cupriavidus necator and Pseudomonas citronellolis in apple pulp wastePublication . Rebocho, Ana Teresa; Pereira, João R.; Neves, Luísa A.; Delgado Alves, Vitor; Sevrin, Chantal; Grandfils, Christian; Freitas, Filomena; Reis, Maria A.M.The co-culture of Cupriavidus necator DSM 428 and Pseudomonas citronellolis NRRL B-2504 was performed using apple pulp waste from the fruit processing industry as the sole carbon source to produce poly(3-hydroxybutyrate), P(3HB) and medium-chain length PHA, mcl-PHA, respectively. The polymers accumulated by both strains were extracted from the co-culture’s biomass, resulting in a natural blend that was composed of around 48 wt% P(3HB) and 52 wt% mcl-PHA, with an average molecular weight of 4.3 105 Da and a polydispersity index of 2.2. Two melting temperatures (Tm) were observed for the blend, 52 and 174 C, which correspond to the Tm of the mcl-PHA and P(3HB), respectively. P(3HB)/mcl-PHA blend films prepared by the solvent evaporation method had permeabilities to oxygen and carbon dioxide of 2.6 and 32 Barrer, respectively. The films were flexible and easily deformed, as demonstrated by their tensile strength at break of 1.47 0.07 MPa, with a deformation of 338 19% until breaking, associated with a Young modulus of 5.42 1.02 MPa. This study demonstrates for the first time the feasibility of using the co-culture of C. necator and P. citronellolis strains to obtain a natural blend of P(3HB)/mcl-PHA that can be processed into films suitable for applications ranging from commodity packaging products to high-value biomaterials