Carlos R. Carrara

A method for evaluating lactose hydrolysis in a fixed bed reactor with β-galactosidase immobilized on chitosan

Abstract A model for evaluating lactose hydrolysis with immobilized enzyme in a packed bed reactor was developed. It is assumed that the conditions were plug flow and Michaelis-Menten kinetics with product competitive inhibition. The effects on the reaction rate of the external mass transfer resistance were considered by estimating the total fluid mass transfer coefficient. Experimental results were determined using β -galactosidase of Kluyveromices fragilis immobilized on chitosan beads in a packed bed reactor under special conditions, in order to calculate the parameters for different flow ranges and substrate concentrations. The model with these values allowed us to fit the reactor behavior for a wider range of work.

The role of cobalt as promoter of equilibrated vanadium–phosphorus–oxygen catalysts

Catalysts were prepared containing between 1% and 6% of Co by weight. The cobalt was either added during preparation or impregnated on the dry VPO precursor. The catalytic evaluation showed that the cobalt-impregnated solids gave the highest yields to maleic anhydride. To understand the promoting effect of cobalt, the catalysts were characterized using XRD, FTIR, SEM, TPR, Raman spectroscopy and XPS. The solids obtained through the addition of Co during the synthesis of the VPO precursor exhibit less disordered crystalline phases in the (001) direction. No separate Co-containing phase could be detected through the techniques used. In the non-equilibrated catalysts, V(V)-containing phases were detected through Raman spectroscopy. After 500 h on stream under reaction conditions (equilibrated catalysts), vanadyl pyrophosphate was the only crystalline phase detected while V(IV) was the only surface species observed using XPS. XRD, FTIR and SEM coincidentally show that depending on the way cobalt is added the solids obtained develop different structural features.

Prediction of the fixed-bed reactor behaviour using dispersion and plug-flow models with different kinetics for immobilised enzyme

Abstract The behaviour of fixed-bed reactors, which have an immobilised enzyme on the packing surface, was studied considering steady-state conditions and external mass transfer resistance in the fluid around catalyst spherical particles. Solutions were obtained by integration of the plug-flow model equation and by the orthogonal collocation method of the second order differential equation of the axial dispersion flow model. Both models were analysed for lactose hydrolysis with β-galactosidase immobilised on chitosan using different kinetic reaction mechanisms after determining the specific parameters. The calculated results show the importance of the hydrodynamic and kinetic reaction parameters for error reduction in the prediction of the experimental behaviour.

Chromatographic fractionation and molecular mass characterization of Cercidium praecox (Brea) gum.

BACKGROUND Brea gum (BG) is an exudate from the Cercidium praecox tree that grows in semi-arid regions of Argentina. Some previous studies on BG have shown physicochemical characteristics and functional features similar to those of gum arabic. However, there is a need to elucidate the molecular structure of BG to understand the functionality. In this sense, BG was fractionated using hydrophobic interaction chromatography and the obtained fractions were analyzed by size exclusion chromatography. RESULTS Analysis of the fractions showed that the bulk of the gum (approx. 84% of the polysaccharides) was a polysaccharide of 2.79 × 10(3)  kDa. The second major fraction (approx. 16% of the polysaccharides) was a polysaccharide-protein complex with a molecular mass of 1.92 × 10(5)  kDa. A third fraction consisted of protein species with a wide range of molecular weights. The molecular weight distribution of the protein fraction was analyzed by size exclusion chromatography. Comparison of the elution profiles of the exudates in native and reducing conditions revealed that some of the proteins were forming aggregates through disulfide bridges in native conditions. Further analysis of the protein fraction by SDS-PAGE showed proteins with molecular weight ranging from 6.5 to 66 kDa. CONCLUSIONS The findings showed that BG consists of several fractions with heterogeneous chemical composition and polydisperse molecular weight distributions.

The nature of the cobalt salt affects the catalytic properties of promoted VPO

Cobalt-impregnated VPO catalysts containing 2 and 4% of the metal by weight were prepared using two different cobalt salts. The catalytic tests showed that cobalt impregnation significantly increased the overall activity. The use of cobalt acetylacetonate led to a more selective high loading catalyst. To investigate the origin of the cobalt effect, the solids were characterized using XRD, Raman Spectroscopy, FTIR and XPS. No structural effects were detected through XRD. After several hundred hours on stream, the only phase detected in all cases was V(Iv) vanadyl pyrophosphate. The surface oxidation state of vanadium was V(Iv). The Co 2p XPspectrum has an intense shoulder at 788 eV, indicating that Co(II) species are present.

Brea gum as wall material in the microencapsulation of corn oil by spray drying: Effect of inulin addition

Abstract This study aimed to evaluate the potential of Brea gum (BG) in the microencapsulation of corn oil in comparison with gum arabic (GA) and evaluate the effect of adding inulin at the matrix formulation. Different concentration of BG and inulin were used to emulsify pure corn oil using a homogenizer followed by an ultrasonic treatment. Then, emulsions were spray dried in laboratory scale equipment to obtain the microcapsules. Overall, powders presented spherical shape with surface concavities, no apparent cracks and high polydispersity. However, some powders containing inulin showed particles that seem to have fused together reflecting a coating effect of inulin. Moisture content of BG powders were low but increased with inulin addition, while water activities (˂0.4) were not affected by inulin. The color analysis showed that BG powders presented lower luminosity and higher red and yellow parameters than GA powder, and adding inulin decreased the lightness, redness and yellowness resulting in powders with more pale color. Encapsulation efficiency increased with BG concentration, reaching 76.12% with 20% of BG. Further efficiency improvement was achieved in presence of inulin, reaching the highest value (91.72) with 20% BG/20% inulin formulation, which was higher than the efficiency achieved with GA (88.66%). It was concluded that the combination of BG and inulin could be used as an alternative wall material for microencapsulation of hydrophobic compounds in replacement of GA.

Development of edible films obtained from submicron emulsions based on whey protein concentrate, oil/beeswax and brea gum

Edible films with whey protein concentrate (WPC) with a lipid component, sunflower oil (O) or beeswax (W), to enhance barrier to water vapor were obtained. Brea gum was used as emulsifier and also as matrix component. In order to achieve emulsion with small and homogeneous droplet size, an ultrasonicator equipment was used after obtaining a pre-emulsion using a blender. The films were made by casting. Effects of lipid fraction on droplet size, zeta potential, mechanical properties, water vapor permeability (WVP), solubility, and optical properties were determined. The droplet size of emulsions with BG decreased when decreasing the lipid content in the formulation. The zeta potential was negative for all the formulations, since the pH was close to 6 for all of them and pI of BG is close to 2.5, and pI of ß-lactoglobulin and α-lactalbumin (main proteins in WPC) are 5.2 and 4.1, respectively. Increasing W or SO content in blended films reduced the tensile strength and puncture resistance significantly. BG and WPC films without lipid presented better mechanical properties. The presence of lipids decreased the WVP, as expected, and those films having BG improved this property. BG films were slightly amber as a result of the natural color of the gum. BG has shown to be a good polysaccharide for emulsifying the lipid fraction and improving the homogeneity and mechanical properties of the films with WPC and beeswax or oil.