Physicochemical and morphological properties of plasticized poly(vinyl alcohol)-agar biodegradable films.

The effects of the addition of glycerol (GLY) on the physicochemical and morphological properties of poly(vinyl alcohol) (PVA)-agar films were reported. PVA-agar films were prepared by solution cast method, and the addition of GLY in PVA-agar films altered the optical properties, resulting in a decrease in opacity values and in the color difference (ΔE) of the films. Structural characterization using Fourier transformation infrared (FTIR) spectroscopy and X-ray diffraction (XRD) indicated that the presence of GLY altered the intensity of the bands (from 1200 to 800cm(-1)) and crystallinity. The characterization of the thermal properties indicated that an increase in the agar content produces a decrease in the melting temperature and augments the heat of fusion. Similar tendencies were observed in plasticized films, but at different magnification. The formulation that demonstrated the lowest mechanical properties contained 25wt.% agar, whereas the formulation that contained 75wt.% agar demonstrated a significant improvement. The water vapor transmission rate (WVTR) and surface morphology analysis demonstrated that the structure of PVA-agar films is reorganized upon GLY addition. The physicochemical properties of PVA-agar films using GLY as a plasticizer provide information for the application of this formulation as packaging material for specific food applications.

Thermal characterization of magnetically aligned carbonyl iron/agar composites.

Composites of magnetic particles into polymeric matrices have received increasing research interest due to their capacity to respond to external magnetic or electromagnetic fields. In this study, agar from Gelidium robustum has been chosen as natural biocompatible polymer to build the matrix of the magnetic carbonyl iron particles (CIP) for their uses in biomedical fields. Heat transfer behavior of the CIP-agar composites containing different concentrations (5, 10, 15, 20, 25 and 30% w/w) of magnetically aligned and non-aligned CIP in the agar matrix was studied using photothermal radiometry (PTR) in the back-propagation emission configuration. The morphology of the CIP-agar composites with aligned and non-aligned CIP under magnetic field was also evaluated by scanning electron microscopy (SEM). The results revealed a dominant effect of CIP concentration over the alignment patterns induced by the magnetic field, which agrees with the behavior of the thermal diffusivity and thermal conductivity. Agar served as a perfect matrix to be used with CIP, and CIP-agar composites magnetically aligned at 20% CIP concentration can be considered as promising 'smart' material for hyperthermia treatments in the biomedical field.

Evaluation of selected tropical seaweeds for in vitro anti-trichomonal activity.

ETHNOPHARMACOLOGICAL RELEVANCE: Human parasitic infections are a serious problem in tropical and sub-tropical developing countries. Trichomoniasis, responsible for the annual infection of 180 million people, is a common sexually transmitted disease caused by the protozoan Trichomonas vaginalis. Traditionally seaweeds have been used in folk medicine by coastal people in Asia and the Caribbean to treat parasitic infections and are a valuable source of novel anti-trichomonals. AIM OF THE STUDY: In our search for therapeutical alternatives to anti-protozoal chemotherapy, we collected a selection of 25 tropical seaweeds (12 Rhodophyta, 5 Phaeophyta and 8 Chlorophyta) from the coast of Yucatan (Mexico) in order to undertake ethnopharmacological and chemotaxonomic investigations. MATERIALS AND METHODS: Organic algal extracts were tested for their anti-trichomonal properties on the growth inhibition of Trichomonas vaginalis. The cytotoxicity of seaweed extracts on mammal cell lines was also assessed. RESULTS: The results indicated that 44% of the seaweeds studied had high to moderate anti-trichomonal activity. Lobophora variegata and Udotea conglutinata showed the maximal anti-trichomonal activity with IC(50) values of 1.39 and 1.66microg/ml, respectively, with good selectivity. CONCLUSIONS: Lobophora variegata and Udotea conglutinata demonstrated promising anti-trichomonal potential and have been selected for further bio-guided fractionation and isolation of active anti-trichomonal compounds.

Antileishmanial properties of tropical marine algae extracts.

Aqueous and organic extracts of twenty-seven species of marine algae (14 species of Rhodophyta, 5 species of Phaeophyta and 8 species of Chlorophyta) collected from the Gulf of Mexico and Caribbean coast of the Yucatan Peninsula (Mexico) were evaluated for their antileishmanial in vitro activity against Leishmania mexicana promastigote forms. The cytotoxicity of these extracts was also assessed using brine shrimp. Organic extracts from Laurencia microcladia (Rhodophyta), Dictyota caribaea, Turbinaria turbinata and Lobophora variegata (Phaeophyta) possessed promising in vitro activity against L. mexicana promastigotes (LC(50) values ranging from 10.9 to 49.9 microg/ml). No toxicity of algal extracts against Artemia salina was observed with LC50 ranging from 119 to >or=1000 microg/ml. Further studies on bio-guided fractionation, isolation and characterization of pure compounds from these species as well as in vivo experiments are needed and are already in progress.

Optimization of native agar extraction from Hydropuntia cornea from Yucatán, México.

Response surface methodology (RSM) was used to determine optimum extraction conditions for yield, gelling temperature, melting temperature and apparent viscosity of native agar from the red alga Hydropuntia cornea. Two independent variables were selected during extraction, temperature (80, 90 and 100 degrees C) and time (2, 3 and 4 h). The extraction procedure using 100 degrees C and 3 h produced the greatest yield (43.3%), the greatest gelling temperature (32 degrees C) and the greatest melting temperature (78 degrees C). The extraction using 65 degrees C and 4 h produced the optimum statistical apparent viscosity (80.73 cPs), though agar yield under these conditions had low quality for industrial purposes. Temperature and time do not affect melting temperature, but do play an important role in gelling temperature. From the independent variables studied, extraction temperature is most important in producing an increase in yield, and time is the only variable that contributes significantly to increasing viscosity. Most of the physicochemical properties found in the native agar from H. cornea extracted at 100 degrees C/3 h were similar to commercial samples. These findings suggest the feasibility of using this colloid in spreads and soft-texture food products.

Agars from three species of Gracilaria (Rhodophyta) from Yucatán Peninsula.

Gracilaria cervicornis, Gracilaria blodgettii and Gracilaria crassissima growing along the coasts of Yucatán were investigated for their agar content. The effect of different concentrations of NaOH in the alkali treatment was evaluated. The three species of Gracilaria produced agars, both native and alkali treated, with different properties confirming the heterogeneity of the agar polymers in this genera. G. cervicornis produces agar polymers with an occurrence of methoxylation and sulphation at the C-6 of the beta-D-galactose residues, and with an extra methylation due to the presence of the 4-O-methyl-alpha-L-galactose residue. The presences of these residues is responsible for the extremely poor gelling ability of its agarocolloids, whose commercial value seems to be quite low. Agar extracts from G. blodgettii showed the typical pattern of unsubstituted agar with a very low degree of methylation on both galactose residues. The discrepancy found between sulphate content and NMR data of agar from this species requires a more detailed structural investigation. G. crassissima produces a good quality agar after sulphate precursor sequences have been removed by alkaline treatment, and it may be considered for exploitation as a source of commercial grade agar. Alkali treatment was effective both in removing alkali-labile sulphate and increasing the gel strength in G. crassissima but not in G. cervicornis and G. blodgettii.