Marcelo Kaminski Lenzi

Vacuum Drying Kinetics of Yacon (Smallanthus sonchifolius) and the Effect of Process Conditions on Fractal Dimension and Rehydration Capacity

This work aimed at studying the drying kinetics of yacon slices during vacuum drying and evaluating the effect of drying temperature, slice thickness, and citric acid concentration in the enzymatic inhibition solution on the fractal dimension and rehydration ratio of yacon slices. The drying kinetics was tentatively fitted to various thin-layer drying models, and the best fit was obtained using the modified Page model. The fit was validated after evaluating the values of coefficient of determination and parameters percentage error. The final products fractal dimension, as calculated by the box counting method, was be between 1.5904 and 1.8358, which confirms that vacuum-dried yacon slices are fractals. Among the studied factors, drying temperature was found to negatively affect the fractal dimension and slice thickness was found to negatively affect the rehydration ratio. A good correlation was established between fractal dimension and moisture content, rehydration ratio, and hue angle, suggesting that the moisture, rehydration, and color measurements during yacon vacuum drying could be substituted or complemented by an image analysis.

Detecting core-shell structure formation using near infrared spectroscopy

It is well known that the final end-use properties of polymer resins depend on several variables. Among them, the morphological aspects of the polymer resin have received considerable attention over the last few years. Particularly, efforts have been devoted towards the study and production of core-shell polymer particles, which find many applications as supports; chromatographic packing among others. Recently, Lenzi et al.1 developed a new process, that combines typical suspension and emulsion polymerisation recipes, to produce polystyrene core-shell particles. In this work, it is shown that NIR spectroscopy can be used as an alternative tool as an in-line system (for in situ detection) of the formation of the core-shell structure in polystyrene core-shell polymer particles produced during simultaneous suspension/emulsion polymerisations.

Effect of grilling and baking on physicochemical and textural properties of tilapia (Oreochromis niloticus) fish burger.

The influence of two common cooking methods, grilling and baking, on chemical composition, water retention, fat retention, cooking yield, diameter reduction, expressible water, color and mechanical texture of tilapia (Oreochromis niloticus) fish burgers was investigated. Texture analyses were performed using a Warner-Bratzler test. The fish burger had a softer texture with a lower shear force than other meat products reported in the literature. There were no significant differences in proximate composition, diameter reduction, fat retention and expressible water between the grilled and oven-baked fish burgers. Cooking methods did not affect the cooking times and cooking rates. Warner-Bratzler parameters and color were significantly influenced by the cooking method. Grilling contributed to a shear force and work of shearing increase due to the lower cooking yield and water retention. Raw burgers had the highest L* (69.13 ± 0.96) and lowest b* (17.50 ± 0.75) values. Results indicated that baking yielded a product with better cooking characteristics, such as a desired softer texture with lower shear values (4.01 ± 0.54) and increased water retention (95.82 ± 0.77). Additionally, the baked fish burgers were lighter (higher L*) and less red (lower a*) than the grilled ones.

Nonlinear diffusion equation and nonlinear external force: Exact solution

The solutions of the nonlinear diffusion equation ∂tρ=r1−ND∂r{rN−1−θργ∂r[r−ηρν]}−r1−N∂r[rN−1Fρ] are investigated by considering the presence of an external force F which exhibits an explicit dependence on the distribution. First, the stationary case is considered; after that the dynamical case, i.e., the case dependent on time. The stationary solution is obtained by considering the external force F(r;ρ)=F1(r)+F2(r)[ρ(r)]ν+γ−1 and the result found is related to the distributions which emerge from the Tsallis statistics or the Boltzmann-Gibbs statistics. The dynamical solution is investigated by considering the external force F(r,t;ρ)=−k(t)r+K∕r1+θ+η[ρ(r,t)]γ+ν−1 and related to the Levy distributions in the asymptotic limit. In both cases, the solutions are expressed in terms of the q-exponentials and the q-logarithmics functions which emerge from the Tsallis formalism.

Modeling Heavy Metal Sorption Kinetics Using Fractional Calculus

Heavy metals are commonly regarded as environmentally aggressive and hazardous to human health. Among the different metals, lead plays an important economic role due to its large use in the automotive industry, being an essential component of batteries. Different approaches have been reported in the literature aimed at lead removal, and among them a very successful one considers the use of water hyacinths for sorption-based operation. The modeling of the metal sorption kinetics is a fundamental step towards in-depth studies and proper separation equipment design and optimization. Fractional calculus represents a novel approach and a growing research field for process modeling, which is based on the successful use of derivatives of arbitrary order. This paper reports the modeling of the kinetics of lead sorption by water hyacinths (Eichhornia crassipes) using a fractional calculus. A general procedure on error analysis is also employed to prove the actual fractional nature of the proposed model by the use of parametric variance analysis, which was carried out using two different approaches (with the complete Hessian matrix and with a simplified Hessian matrix). The joint parameter confidence regions were generated, allowing to successfully show the fractional nature of the model and the sorption process.

Solutions for a fractional nonlinear diffusion equation with external force and absorbent term

We devote this work to investigate the solutions of a -dimensional nonlinear fractional diffusion equation which emerges from the continuity equation by considering a nonlinear fractional generalization of Darcy law and incorporating an absorbent term. The solutions obtained show a nonusual spreading of the distribution and a compact or long tail behavior which can be related to the anomalous diffusion.

Fractional diffusion equation, boundary conditions and surface effects

We investigate a system governed by a fractional diffusion equation with an integro-differential boundary condition on the surface. This condition can be connected with several processes such as adsorption and/ or desorption or chemical reactions due to the presence of active sites on the surface. The solutions are obtained by using the Green function approach and show a rich class of behaviors, which can be related to anomalous diffusion.

Intermittent Motion, Nonlinear Diffusion Equation and Tsallis Formalism

We investigate an intermittent process obtained from the combination of a nonlinear diffusion equation and pauses. We consider the porous media equation with reaction terms related to the rate of switching the particles from the diffusive mode to the resting mode or switching them from the resting to the movement. The results show that in the asymptotic limit of small and long times, the spreading of the system is essentially governed by the diffusive term. The behavior exhibited for intermediate times depends on the rates present in the reaction terms. In this scenario, we show that, in the asymptotic limits, the distributions for this process are given by in terms of power laws which may be related to the q-exponential present in the Tsallis statistics. Furthermore, we also analyze a situation characterized by different diffusive regimes, which emerges when the diffusive term is a mixing of linear and nonlinear terms.

Liquid-liquid Equilibrium in Systems Containing Olive Oil, Free Fatty Acids, Ethanol and Water

This paper reports experimental data and the thermodynamic modeling of the liquid-liquid equilibrium systems with triacylglycerols, free fatty acids (obtained from olive oil), ethanol and water. The experimental data were fitted using the UNIQUAC model, in which absolute deviation of 1.28 % and root mean square deviation of 2.10 % between experimental and calculated mass fraction of the components in each phase were obtained. The results from this study can be complementary to investigations of more complex liquid-liquid equilibrium of systems containing diacylglycerols and monoacylglcerols of olive oil in hydroalcoholic solutions, once such systems will mostly also contain triacylglycerols and free fatty acids on its composition. Diacylglycerols are obtained from different reaction processes and can be purified by liquid-liquid extraction at mild conditions of temperature and pressure, what justifies the experimental and theoretical approach made in this work.

Use of image analysis for monitoring the dilution of Physalis peruviana pulp

The aim of this work was to develop linear models using the image analysis coupled with density measurements to monitor the dilution of the Physalis juice in the concentrations ranging from 0 to 100% in mass of juice pulp. A sample corresponding to 20% in the mass of juice pulp was for validating purposes and a prediction of 19.9±0.3%. The models with three parameters showed the best predictions, providing this technique with a promising future for the monitoring the dilution of fruit juices.