Maria G. Carneiro-da-Cunha

Nanoemulsions of β-carotene using a high-energy emulsification–evaporation technique

Nanoemulsions of b-carotene were prepared using a high-energy emulsification-evaporation technique based on a 2 3 level factorial design. Results show that it is possible to obtain dispersions at a nanoscale range. Process parameters such as time and shear rate of homogenization affected significantly particle size distribution in terms of volume-weighted mean diameter and surface-weighted mean diameter. The obtained nanoemulsions presented a volume-surface diameter ranging from 9 to 280 nm immedi- ately after the production of particles, displaying in all cases a monomodal size distribution. Those nano- emulsions showed a good physical stability during 21 days storage. The stability was evaluated by the maintenance of size distribution. However, b-carotene retention inside the micelles and color were affected by storage. Processing conditions also influenced storage stability.

Purification of a lectin from Eugenia uniflora L. seeds and its potential antibacterial activity

Aims:  The aim of this work was to analyse the antimicrobial properties of a purified lectin from Eugenia uniflora L. seeds.

Coagulant and antibacterial activities of the water-soluble seed lectin from Moringa oleifera

Aims:  The aim of this work was to analyse the coagulant and antibacterial activities of lectin isolated from Moringa oleifera seeds that are used for water treatment.

Characterization and rheological study of the galactomannan extracted from seeds of Cassia grandis.

Galactomannan extracted from seeds of Cassia grandis with 0.1M NaCl, followed by ethanol precipitation, presented a yield of 36 ± 8%. The polysaccharide has a constant mannose/galactose ratio (2.44:1). Methylation analysis, one and two dimensional NMR spectroscopy confirmed that the polysaccharide has a central core composed of 4-linked β-mannose units, with branches of galactose, linked to the carbohydrate core through α(1-6) linkage. The amorphous nature of the galactomannan was confirmed by X-ray diffraction. Rheological characterization exhibited Newtonian plateaus followed by shear-thinning zones characteristic of polymer solutions up to 1.5% (w/v) and above this value the system exhibited yield stress associated with a weak gel. Adjusting stress-strain curves confirmed a 1.6% (w/v) as the galactomannan concentration value for the sol-gel transition. These results indicate that the galactomannan extracted from C. grandis seeds presents rheological characteristics suitable for applications in pharmaceutical, biomedical, cosmetic and food industries.

Crataeva tapia bark lectin is an affinity adsorbent and insecticidal agent

Hemagglutinating activity has been associated to presence of lectin, carbohydrate-binding proteins. In this work Crataeva tapia bark lectin (CrataBL) was purified in milligram quantities (28 mg per g of bark) by ion exchange chromatography. The lectin was thermo-stable, ion-independent and N-terminal sequence analysis demonstrated similarity with miraculin and miraculin-like proteins (plant defensive proteins). Glycosylated nature of CrataBL was revealed using glycoprotein staining (periodic acid-Schiffs reagent), positive for polypeptides of apparent molecular masses 21 and 40 kDa on SDS-PAGE. Gel diffusion assay showed that glucose/mannose isolectins from Cratylia mollis recognized CrataBL glycan moiety. CrataBL hemagglutinating activity was inhibited by glycoproteins and CrataBL immobilized on cyanogen bromide-activated sepharose 4B (1 mL) bound 0.54 mg of glycoprotein (casein, fetuin and ovalbumin) per cycle. CrataBL was an insecticide agent against Nasutitermes corniger workers (termite that attack woods) with LC₅₀ of 0.475 mg mL⁻¹ for 6 days.

Development and Characterization of an Active Chitosan-Based Film Containing Quercetin

This work aims at developing an active chitosan film through the incorporation of quercetin and the evaluation of physical and functional properties of the films made thereof. The addition of quercetin showed to influence films’ properties in terms of surface morphology, tensile strength, and opacity while elongation-at-break, thickness, water vapor, and oxygen permeability were not significantly affected with incorporation of quercetin. The color parameters of chitosan films were affected by quercetin incorporation with a decrease of the values of L* and a*. The film exhibited a high free-radical scavenging activity, showing antioxidant activity. The film-forming solutions of chitosan with or without quercetin showed antibacterial activity against four Gram-negative and three Gram-positive bacteria. These results showed that quercetin incorporation in chitosan-based films has potential to be used as a solution for active food packaging.

Purification of a lectin from Canavalia ensiformis using PEG-citrate aqueous two-phase system.

A PEG/citrate aqueous two-phase system was tested in the partition of commercial Concanavalin A (Con A) and subsequently applied to the extraction and purification of Con A from the crude extract of Canavalia ensiformis seeds. Con A was successfully extracted to the bottom phase of a system composed of 22% (w/w) PEG8000 and 12% (w/w) citrate at pH 6.0. The obtained purification factor was 11.5 without any loss in the hemagglutinating activity. The purity of extracted lectin was confirmed by SDS-PAGE analysis.

Development and characterization of hydrogels based on natural polysaccharides: Policaju and chitosan

The development of hydrogels based on natural polysaccharides was investigated by preparing mixtures of policaju/chitosan at weight ratios of 1:4 and 2:3. Utilizing dynamic light scattering (DLS) techniques for these mixtures, an increase on the hydrodynamic particle radius was observed varying their pH from 3.0 to 12.0. Furthermore, a reduction of ζ-potential was also observed for the same pH interval. Following rounds of drying/hydration cycles at a specific pH value, hydrogel matrices were formed. The pore size distribution of these formed hydrogels was examined using scanning electron microscopy. Further FT-IR analyses confirmed a physical interaction between the polysaccharides policaju and chitosan. Swelling experiments revealed water uptake values, after 24h of immersion in water, close to 270% for 1:4, and 320% for 2:3 hydrogels. Finally, rheological measurements were then conducted in order to confirm hydrogel viscoelastic features. These results indicate a promising road to biomaterials fabrication and biomedical applications.

Development and characterization of a new hydrogel based on galactomannan and κ-carrageenan.

A new hydrogel based on two natural polysaccharides was prepared in aqueous medium with 1.7% (w/v) galactomannan (from Cassia grandis seeds) and different concentrations of κ-carrageenan (0.3, 0.4 and 0.5%w/v), CaCl2 (0.0, 0.1 and 0.2M) and pH (5.0, 5.5 and 6.0), using a full factorial design based on rheological parameters. The best formulation was obtained with 1.7% (w/v) galactomannan and 0.5% (w/v) κ-carrageenan, containing 0.2M CaCl2 at pH 5.0. Nuclear magnetic resonance and scanning electron microscopy where used in order to characterize the hydrogel formulation. A shelf life study was carried out with this formulation along 90 days-period of storage at 4 °C, evaluating pH, color, microbial contamination and rheology. This hydrogel showed no significant changes in pH, no microbial contamination and became more translucent along the aging. Analyses by nuclear magnetic resonance and rheology showed a larger organization of the polysaccharides in the hydrogel matrix. The results demonstrated that this hydrogel was stable with possible applications in medical and cosmetic fields.

Polysaccharide from Anacardium occidentale L. tree gum (Policaju) as a coating for Tommy Atkins mangoes

Policaju-based coatings were applied on “Tommy Atkins” mangoes and the effects of four different treatments on mango shelf-life were evaluated under storage condition at 4°C and 82 % of relative humidity over 28 days. The surface tension of mangoes was found to be 29.04 mN m−1; the dispersive and polar components were 27.57 mN m−1 and 1.47 mN m−1, respectively, and the critical surface tension was 22.7 mN m−1. A significantly lower mass loss was observed in all mangoes treated with Policaju-based coatings. For all applied treatments, no significant variation in the total soluble solids and pH was detected over the experimental storage time. The results show that Policaju-based coatings have a positive effect on the shelf-life extension of mangoes at low storage temperatures (4°C).