Effect of Lactobacillus plantarum and chitosan in the reduction of browning of pericarp Rambutan (Nephelium lappaceum)

The effects of Lactobacillus plantarum alone or in combination with chitosan were evaluated on quality and color retention in rambutan fruits (Nephelium lappaceum) stored at 25 °C and 10 °C with 75 ± 2.5% of relative humidity for 10 and 15 days, respectively. The development of the microorganisms was evidenced by viability analyses and lactic acid production. The application of L. plantarum significantly improved color retention (a* and L*), and reduced weight losses. The lactobacilli, alone or in combination with chitosan, preserved fruit quality characteristics such as firmness, total soluble solids and titratable acidity. The lactobacilli application on rambutan pericarp produced acidification of pericarp and avoided the browning; thereby desiccation was prevented due to biofilm formation.     

Characterization of La2−xSrxCoTiO6 (0.6 ≤ x ≤ 1.0) series as new cathodes of solid oxide fuel cells

La_2−xSr_xCoTiO₆ (0.6 ≤ x ≤ 1.0) compound series is prepared by Sr-substitution in the A-site of the perovskite by a modified Pechini procedure under air. Charge compensation as Sr²⁺ content increase occurs by Co²⁺ oxidation to Co³⁺. Reduced samples are obtained by further treatment under 5%H₂/Ar and characterized by Neutron Powder Diffraction. Upon redution, Co³⁺ to Co²⁺ reduction and oxygen vacancies creation are detected. Dependence of total conductivity with temperature and pO₂ exhibits a typical p-type semiconducting behaviour. Results show that the higher the Sr content, the higher holes (Co³⁺) concentration and consequently, La_2−xSr_xCoTiO₆ (x = 1.0) shows the highest conductivity (13.23 S/cm at 1073 K in air). The negligible reactivity with YSZ, used as the electrolyte, of symmetrical cells under oxidant conditions and the moderate thermal expansion found by XRD point to their possible use as SOFC cathodes. Thus, La_1.2Sr_0.8CoTiO₆-based cathodes display polarization resistance of 0.9 Ω cm² at 1073 K in oxygen, only slightly above than the current state-of-the-art.     

Linear Programs for the Reconstruction of 2D Images from Geophysical Electromagnetic Measurements

In this paper we present an approach for constructing vertical sections of the electrical conductivity of the earth on the basis of surface measurements. We assume that the conductivity of the earth varies with depth and laterally but not along the third dimension or strike. Electromagnetic measurements are effected every few meters across strike using pairs of horizontal and vertical coils, with the separation between source and receiver varying in order to sample different depths. The data thus provides information about the vertical and horizontal distribution of electrical conductivity of a section of the earth. Recovering the true conductivity distribution from the measurements is a nonlinear inverse problem that allows some useful linear approximations, which we exploit here using linear programming techniques. We apply a regularization approach using -insensitive functions for both, the fitness to the data and the penalizing function. This representation enforces a model structure of blocks immersed in a homogeneous basement, a useful model in many practical instances. Applications of the technique to synthetic and field data in one and two dimensions illustrate the usefulness of the technique.     

Effect of microwave heating during alkaline-cooking of aflatoxin contaminated maize

To evaluate the effectiveness of maize detoxification achieved with a modified tortilla-making process (MTMP), maize contaminated with aflatoxin B(1) (AFB(1)) and aflatoxin B(2) (AFB(2)) at levels of 22.46, 69.62, and 141.48 ng/g (AFB(1)+ AFB(2)) was processed into tortillas. Aflatoxin content was determined according to the 991.31 AOAC official method. Based on the results obtained with spiked samples (0.78 to 25 ng/g), the mean recovery was 92%, with a standard error of 1.2, and a coefficient variation value of 4.4%. The MTMP caused 68, 80, and an 84% decrease in aflatoxin content, respectively. Extract acidification (as occurs during digestion) prior to mycotoxin quantification caused some reformation of the aflatoxin structure in tortillas (up to 3%). According to these results, the MTMP seems to be safe for decontamination since a low percentage of the initial aflatoxin concentration can be reverted to the original fluorescent form upon acidification. PRACTICAL APPLICATION: The potential presence of aflatoxins in maize destined for human consumption is a serious problem to the Mexican food supply, as these toxic compounds may persist during the traditional alkaline-process for tortilla elaboration. Consequently, new detoxification procedures are needed that eliminate or at least minimize the aflatoxin risk, through lowering aflatoxin concentration in maize-based products. Under these considerations, the use of MTMP is recommended, since it has definite advantages including non-production of wastewater and reduced energy/time consumption.     

Structural and electrochemical characterization of La2−xSrxNiTiO6−δ

Materials of the series La_2−xSr_xNiTiO_6−δ (0 ≤ x ≤ 0.5) have been characterized by both structural and electrochemical methods in order to assess their possible use as electrodes for SOFCs. Neutron and X-ray powder diffraction experiments have shown that they are stable under both oxidizing and reducing conditions while chemically compatible with YSZ at SOFC operating temperatures. Moreover, the thermal expansion has been determined to be isotropic with α_L = 10.0(3) × 10⁻⁶ K⁻¹. This value is similar to that found for other perovskite materials used in SOFCs. However, polarization resistances reveal modest values of electrochemical response under oxygen (1.5 Ω cm² at 900 °C) and are quite poor in 5%H₂/N₂ mixtures (15 Ω cm²) at the same temperature. Nevertheless, microstructure has not been optimized fully enough to discard the material as a potential SOFC cathode.     

Some physicochemical and antinutritional properties of raw flours and protein isolates from Mucuna pruriens (velvet bean) and Canavalia ensiformis (jack bean)

The legumes Canavalia ensiformis and Mucuna pruriens are underexploited in tropical Mexico. Their seeds have good nutritional potential, but contain antinutritional factors. Physicochemical and antinutritional properties were determined for raw flours (RF) and protein isolates (PI) produced from these legumes. Protein content in the PI was 737 g kg^–1 for C. ensiformis and 666 g kg^–1 for M. pruriens. Protein isolation improved in vitro digestibility, while maintaining high lysine levels and adequate sulphur amino acids content. Antinutritional factors such as cyanogenic glucosides, cyanide precursors from hydrolysis, tannins and trypsin inhibitors were lower in the PIs than in the RFs. The reduction in canavanine levels, a structural analogue of arginine, in the C. ensiformis PI was noteworthy. These PIs thus have potential applications in the development of new food ingredients in tropical regions using processes that improve nutritional value.     

Maize and bean storage and their use by rural farmers in a Central state of Mexico

A study was carried out in the rural areas of the state of Guanajuato in Central Mexico to identify the way in which two different types of farmer store and use their maize and bean production. One of these groups of farmers utilizes a communal type of land named ejido, whereas the others own their property. It was found that the ejido farmers store between 1–2 tons of these basic products, to be used for seed (0.1–0.3 tons), home consumption (<1 ton), and possibly subsequent sale (<1 ton). However, the private property farmers have the option of storing more than the ejido farmers, and although they also cover the above mentioned needs, they usually have a surplus of these commodities for market (1–5 tons). The data indicate that both types of farmer (56%) lack adequate storage facilities, and store their maize and beans in rooms, which are also used for storing other commodities. The study shows that both types of farmer need information on appropriate technologies that would assist them in preventing the deterioration of these crops due to insect and rodent infestation. The interviewed farmers reported these pests are the main causes of damage to stored maize and beans.     

Analysis of performance losses of direct methanol fuel cell with methanol tolerant PtCoRu/C cathode electrode

The long-term stability of PtCoRu/C to methanol crossover has been evaluated in a direct methanol fuel cell (DMFC) configuration. The DMFC has been subjected to continuous operation under potential step cycles. The degradation of the DMFC with PtCoRu/C has been followed by comparison of the power density curves recorded after 0, 60 and 312 h of continuous operation, and compared to that recorded for a DMFC with Pt/C. Electrochemical Impedance Spectra (EIS) were recorded directly from the DMFCs and used to identify the main degradation phenomena responsible for the loss of performance of the used fuel cell. AC impedance spectra show that the resistance of the anode reaction increases while resistance associated to the cathode reaction decreases after the long-term stability tests; however, the analysis of the power density curves unequivocally show that the performance of the DMFCs goes down during the stability tests. This apparent contradiction can be explained by taking into account the changes between the fresh and used PtCoRu/C observed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses. During the potential step cycles Ru dissolves form PtCoRu/C leading to Pt-enriched catalysts which are more active for the oxygen reduction reaction (lower resistance) but less tolerant to methanol (lower power density).     

Electrochemical performances of BiSbO4 as electrode material for lithium batteries

We present an electrochemical study of BiSbO₄, an opened layered oxide having a structure related to Aurivillius phases. Li//BiSbO₄ cells show a large specific capacity as high as 1250 mAh g⁻¹ during reduction down to 0.5 V. This reaction involves 18Li atoms per formula unit, pointing it towards a very promising cathode material for primary lithium batteries, in particular for ICD devices. The characterization of the reduction products indicates that the reduction of BiSbO₄ with lithium presumably goes along firstly with the formation of metallic Sb and Bi to follow the formation of the alloys Li₃Bi and Li₃Sb dispersed in a lithium oxide matrix. In situ X-ray diffraction experiments proved the amorphous nature of both metals and final alloys. On the other hand when Li//BiSbO₄ cells are limited to discharge down to 1.2 V, BiSbO₄ reacts with 5Li atoms. After the first discharge, that develops a specific capacity of 350 mAh g⁻¹, high cyclability has been observed.