Maribel Jiménez-Fernández

Bioleaching of gold, copper and nickel from waste cellular phone PCBs and computer goldfinger motherboards by two Aspergillus nigerstrains

In an effort to develop alternate techniques to recover metals from waste electrical and electronic equipment (WEEE), this research evaluated the bioleaching efficiency of gold (Au), copper (Cu) and nickel (Ni) by two strains of Aspergillus niger in the presence of gold-plated finger integrated circuits found in computer motherboards (GFICMs) and cellular phone printed circuit boards (PCBs). These three metals were analyzed for their commercial value and their diverse applications in the industry. Au-bioleaching ranged from 42 to 1% for Aspergillus niger strain MXPE6; with the combination of Aspergillus niger MXPE6 + Aspergillus niger MX7, the Au-bioleaching was 87 and 28% for PCBs and GFICMs, respectively. In contrast, the bioleaching of Cu by Aspergillus niger MXPE6 was 24 and 5%; using the combination of both strains, the values were 0.2 and 29% for PCBs and GFICMs, respectively. Fungal Ni-leaching was only found for PCBs, but with no significant differences among treatments. Improvement of the metal recovery efficiency by means of fungal metabolism is also discussed.

Oleoresins from Capsicum spp.: Extraction Methods and Bioactivity

Capsicum spp. fruit is one of the most produced vegetables around the world, and it is consumed both as fresh vegetable and as a spice like a food additive for their characteristic red color and, in many cases, its pungency. In addition to its economic importance, the bioactivity of some important compounds such as capsaicinoids and carotenoids has promoted its research. The use of Capsicum oleoresins has been increased due to its advantages comparing with the traditional dry spice. These include obtaining higher quality products with the desired content of bioactive and flavored substances. The wide diversity of extraction methods including water extraction, organic solvent extraction, microwave-assisted extraction, and ultrasound assisted extraction as well as supercritical fluid extraction among others are discussed in the present review. Moreover, pretreatments such as chemical treatments, osmotic dehydration, sun and oven drying, and freeze-drying commonly used before the extraction are also presented. Due to its importance, Capsicum oleoresins produced with “green” solvents and the improvement of fractional extraction techniques that allow to obtain separately the various bioactive fractions will continue under research for further development.

Fluidized Bed Drying Process of Thinly Sliced Potato (Solanum tuberosum)

Potatoes play the role of a vegetable or a complementary dish in the Mexican diet. They are mainly consumed fresh. Dried vegetables of the particular interest in preparation of dry mixtures are used for soups. The rapid expansion of the fast food industry could result in an increase in the use of dehydrated potatoes, as a component for vegetable mixture and soups. However, Pre-drying treatments such as addition of antioxidants are needed for vegetable drying as the potato in order to avoid changes of color. In this work, the influence of different pre-treatments and drying conditions on physical characteristics (moisture content, water activity and color difference) of thinly sliced potato during drying by fluidized bed was investigated. The thinly sliced samples of fresh potato were dipped into solutions containing citric acid (0, 0.5 and 1 % w/w) before drying. Potato sample were dehydrated at air temperatures of 40, 50 and 60 °C. The second degree polynomial model was used to describe the response variables. The analysis of variance (ANOVA) for all coded models indicated that the models were statistically significant (p ≤ 0.05). The temperature and citric acid increment increases color difference, and decreases the moisture content and water activity of the dehydrated samples of potato. Color closest to the original color of fresh potato was obtained in some treatments. In general, it was observed that the drying of thinly sliced potato was influenced by pretreatment.ResumenLas papas juegan un papel como verdura o como guarnición en la dieta Mexicana. Son consumidas principalmente en fresco. En sopas se usan vegetales deshidratados de interés particular en la preparación de mezclas secas. La rápida expansión en la industria de la comida rápida pudiera resultar en un aumento en el uso de papas deshidratadas, como un componente de mezcla de vegetales y sopas. No obstante, los tratamientos de pre-secado, como la adición de antioxidantes, son necesarios para el deshidratado de verduras como la papa, a fin de evitar cambios de color. En este trabajo, se investigó la influencia de diferentes pre-tratamientos y condiciones de secado en las características físicas (contenido de humedad, actividad del agua y diferencia en color) de papa rebanada muy delgada durante el deshidratado mediante cama fluidizada. Las muestras de rebanadas delgadas de papa fresca fueron inmersas en soluciones que contenían ácido cítrico (0, 0.5, y 1% p/v) antes del secado. Las muestras de papa se deshidrataron a temperaturas del aire de 40, 50, y 60 °C. Se usó un modelo polinomial de segundo grado para describir las variables-respuestas. El análisis de varianza (ANAVA) para todos los modelos codificados indicaron que los modelos fueron estadísticamente significativos (p≤0.05). El aumento en la temperatura y el ácido cítrico incrementan la diferencia en color y disminuyen el contenido de humedad y actividad del agua de las muestras deshidratadas de papa. En algunos tratamientos se obtuvo un color cercano al original de la papa fresca. En general, se observó que el secado de rebanadas finas de papa estuvo influenciado por el pre-tratamiento.

Effect of drying methods on the physicochemical and thermal properties of Mexican plum (Spondias purpurea L.)

ABSTRACT Plum slices (diameter 2.5 cm and thickness 0.2 cm) were dried using vertical tray-drying (VTD) and freeze-drying. Models were used to determine the thermal conductivity (k) and specific heat (Cp). In addition, water activity (aw), colour total change (∆E), pectin yield (ypec) and rehydration capacity were investigated. The moisture content of tray- and freeze-dried plum was relatively significant (p < 0.05). No significant difference was found in terms of aw. There was a maximum decrease in k and Cp of 90% and 91.5% during drying process, respectively. In terms of quality, ∆E showed that tray-dried samples had slight darker (browning), whereas the freeze-dried samples had a lighter colouring compared to the fresh fruit. The quality and rehydration characteristics of freeze-dried plum were higher than that of a tray-dried product; however, VTD could be appropriate for industrial production because of its advantages in lower cost and energy consumption.

Transforming the canonical piecewise-linear model into a smooth-piecewise representation

A smoothed representation (based on natural exponential and logarithmic functions) for the canonical piecewise-linear model, is presented. The result is a completely differentiable formulation that exhibits interesting properties, like preserving the parameters of the original piecewise-linear model in such a way that they can be directly inherited to the smooth model in order to determine their parameters, the capability of controlling not only the smoothness grade, but also the approximation accuracy at specific breakpoint locations, a lower or equal overshooting for high order derivatives in comparison with other approaches, and the additional advantage of being expressed in a reduced mathematical form with only two types of inverse functions (logarithmic and exponential). By numerical simulation examples, this proposal is verified and well-illustrated.