José G. Carriazo

Catalytic wet peroxide oxidation of phenol over Al-Cu or Al-Fe modified clays

Al–Fe or Al–Cu modified clays were prepared from two natural montmorillonites and employed in the phenol oxidation with hydrogen peroxide in water. The samples were efficient in phenol elimination under mild experimental conditions (atmospheric pressure, 293 K and small quantities of hydrogen peroxide) without considerable leaching of the metal ions. The clays modified with Fe achieved high conversions of phenol and TOC thus showing to be very selective towards the formation of CO2 and H2O.

Microencapsulation by spray-drying of anthocyanin pigments from corozo (Bactris guineensis) fruit.

The anthocyanins of Bactris guineensis fruit were isolated with the aid of high-speed countercurrent chromatography (HSCCC) and preparative HPLC, and their chemical structures were elucidated by using spectroscopic methods. Among the identified pigments, cyanidin-3-rutinoside and cyanidin-3-glucoside were characterized as major constituents (87.9%). Peonidin-3-rutinoside, peonidin-3-glucoside, cyanidin-3-(6-O-malonyl)glucoside, and cyanidin-3-sambubioside were present in minor amounts. Four anthocyanin ethanolic extracts (AEEs) were obtained by osmotic dehydration and Soxhlet extraction and physicochemically characterized. The composition of anthocyanins was monitored by HPLC-PDA. The extracts with the highest anthocyanin content were subjected to the spray-drying process with maltodextrin. The so-obtained spray-dried powders were analyzed by scanning electron microscopy (SEM) and found to consist of spherical particles <50 microm in size. The anthocyanin composition was similar to that of the fruit. The microencapsulated powders were analyzed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), revealing that they are quite stable until 100 degrees C. Storage stability tests of microcapsules showed that the release of anthocyanin pigments follows pseudo-first-order kinetics and that the process rate is increased by temperature and humidity. The most suitable conditions for storage were below 37 degrees C and <76% relative humidity, respectively.

Microencapsulation of betalains obtained from cactus fruit (Opuntia ficus-indica) by spray drying using cactus cladode mucilage and maltodextrin as encapsulating agents

The microencapsulation of betalains from cactus fruit by spray drying was evaluated as a stabilization strategy for these pigments. The betalains used as active agent were extracted from purple fruits of Opuntia ficus-indica (BE) and encapsulated with maltodextrin and cladode mucilage MD-CM and only with MD. The microcapsulates were characterized by scanning electron microscopy (SEM), thermal analysis (TGA-DSC), tristimulus colorimetry, as well as, their humidity, water activity and dietary fiber content were also determined. The active agent content was measured by UV-Vis spectrophotometry and its composition confirmed by HPLC-ESIMS. A pigment storage stability test was performed at 18 °C and different relative humidities. The addition of CM in the formulation increased the encapsulation efficiency, diminished the moisture content, and allowed to obtain more uniform size and spherical particles, with high dietary fiber content. These microencapsulates are promising functional additive to be used as natural colorant in the food industry.

Thermal and structural study of guava (Psidium guajava L) powders obtained by two dehydration methods

Two food products (powders) were obtained by hot-air drying or lyophilisation methods on the whole guava fruits. The powders were characterised by sensory and thermal analyses (TGA-DSC), infrared spectroscopy (IR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Thermal, morphological and structural characterisations showed a similar behaviour for the two solids. TGA-DSC and IR showed the presence of pectin as the main constituent of solids. A semi-crystalline profile was evidenced by XRD, and lamellar/spherical morphologies were observed by SEM. Sensory analyses revealed an aroma highly related to guava. These value-added food products are an alternative to process guava and avoid loss during postharvest handling.

Encapsulating betalains from Opuntia ficus-indica fruits by ionic gelation: Pigment chemical stability during storage of beads.

Betalain encapsulation was performed by ionic gelation as a stabilization strategy for these natural pigments. Betalains were extracted from purple cactus fruits and encapsulated in calcium-alginate and in combination of calcium alginate and bovine serum albumin. Beads were characterised by scanning electron microscopy and thermal analysis using differential scanning calorimetry and thermogravimetry. Moisture sorption isotherms were determined. Bead morphology was affected by matrix composition. Pigments storage stability was evaluated at different equilibrium relative humidity and temperatures. Pigment composition of beads was determined by HPLC-MS-MS and degradation products were also analysed after storage; betalamic acid being the major one. Both types of matrices protected the encapsulated pigments, being their storage stability better at low relative humidity than that of the non-encapsulated control material. Antiradical activities of beads were proportional to remaining betalain contents. At high relative humidity, there was no protection and low storage stability was observed in the samples.

Characterization of the carbonaceous materials obtained from different agro-industrial wastes

This paper reports the preparation and characterization of carbonaceous materials obtained from three types of vegetable wastes provided by agricultural industries. Soft carbonization (280°C) and H3PO4-activation procedures were used to convert the agricultural wastes to carbon powders with high adsorbent capacities. This process is excellent for eliminating and exploiting the huge masses (many tons) of vegetable residues remaining after each harvest every year in several Colombian agro-industries. The powders were characterized by X-ray diffraction (XRD), IR spectroscopy, scanning electron microscopy (SEM), and N2-adsorption isotherms. XRD and IR verified the formation of carbons, and SEM showed small particles (20–500 µm) with characteristic morphology for each type of residue used and abundant cavities of different sizes. The N2-adsorption analyses showed that the carbons had high adsorption capacities with important surface area values and large pore volumes. The use of the activated carbonaceous materials as adsorbent of azo dyes (allura red and sunset yellow) from aqueous solutions was evaluated. The results showed a good adsorption capacity indicating the potentiality of these materials as pollutant adsorbents in food industry wastewaters. These results indicate that these powders can be used as potential adsorbents for different gaseous or liquid pollutants. GRAPHICAL ABSTRACT

Actividad catalítica de metales de transición en la descomposición de peróxido de hidrógeno

This paper compares the catalytic activities of some transition metal ions (Fe3+, Co2+, Cu2+, Ni2+, Zn2+) in the H2O2 decomposition in homogenous and heterogeneous processes, including solid mixed systems (Fe-Cu-Co/Al2O3, Fe-Cu/Al2O3, Fe-Co/Al2O3 and Co-Cu/Al2O3). The solids were characterised by X-ray diffraction to explore evolution of phases or possible changes. Different trends of the catalytic activity were observed: in homogeneous medium the most active species was Fe3+, whereas in heterogeneous one the higher activities were shown for Co/Al2O3 and Co-Cu/Al2O3. A strong cooperative effect for the Co-Cu/Al2O3 system was observed, which can be considered as a new catalyst of interest for this type of reactions.

Actitudes hacia la química de estudiantes de diferentes carreras universitarias en Colombia

This work reports a study on the attitudes of Colombian students towards Chemistry in different undergraduate programs. The research was performed on 769 students belonging to several Chemistry courses, by applying an adaptation of Salta and Tzougrakis test and using Likerts scale. The results revealed that Chemistry is being considered as difficult and little useful, but very interesting. Thus, the difficulty to learn Chemistry may be associated with its language and abstract conceptual nature. In addition, more attention should be given to the class contents and methodologies provided to the students, in order to engage them with those interest aspects and meaningful topics of each program

Effect of different drying methods on morphological, thermal, and biofunctional properties of lulo (Solanum quitoense Lam.) fruit powders

ABSTRACT Four different powders of dried lulo (Solanum quitoense Lam.) were obtained by hot air drying (HD), ultrasound-assisted hot air-drying (HDUS), freeze-drying (FD), and spray-drying (SD). The morphological (SEM) and thermal (TGA–DSC) characterization were made, and some biofunctional properties such as dietary fiber (DF) content and antioxidant capacity (ABTS and DPPH assays) were evaluated. The homogeneous morphology of SD particles was evident from SEM analysis, in contrast to the irregular morphology of the other dried powders. All of the dried lulo powders were thermally stable until 220°C. Although, the initial composition of the mixtures (fruit pulp/maltodextrin DE-20, 2:1, w/w) was the same, some differences on DF content and antioxidant activity were found, indicating that the drying method influenced significantly the chemical composition of powdered products. A higher insoluble dietary fiber (IDF) percentage was found in FD sample; in contrast, a higher in vitro antioxidant capacity values against ABTS and DPPH free radicals were found for HD and SD powders.

Laboratory projects using inquiry-based learning: an application to a practical inorganic course

This paper reports how laboratory projects (LP) coupled to inquiry-based learning (IBL) were implemented in a practical inorganic chemistry course. Several coordination compounds have been successfully synthesised by students according to the proposed topics by the LP-IBL junction, and the chemistry of a number of metals has been studied. Qualitative data were collected from written reports, oral presentations, lab-notebook reviews and personal discussions with the students through an experimental course with undergraduate second-year students at the Universidad Nacional de Colombia during the last 5 years. Positive skills production was observed by combining LP and IBL. Conceptual, practical, interpretational, constructional (questions, explanations, hypotheses), communicational, environmental and application abilities were revealed by the students throughout the experimental course.