Mario E. Rodríguez-García

Physicochemical, morphological, and rheological characterization of Xanthosoma robustum Lego-like starch

This work presents the physicochemical and pasting characterization of isolated mafafa starch and mafafa flour (Xanthosoma robustum). According to SEM images of mafafa starches in the tuber, these starches form Lego-like shaped structures with diameters between 8 and 35 μm conformed by several starch granules of wedge shape that range from 2 to 7 μm. The isolated mafafa starch is characterized by its low contents of protein, fat, and ash. The starch content in isolated starch was found to be 88.58% while the amylose content obtained was 35.43%. X-ray diffraction studies confirm that isolated starch is composed mainly by amylopectin. These results were confirmed by differential scanning calorimetry and thermo gravimetric analysis. This is the first report of the molecular parameters for mafafa starch: molar mass that ranged between 2×10(8) and 4×10(8) g/mol, size (Rg) value between 279 and 295 nm, and molecular density value between 9.2 and 9.7 g/(mol nm(3)). This study indicates that mafafa starch shows long chains of amylopectin this fact contributes to higher viscosity development and higher gel stability. The obtained gel phase is transparent in the UV-vis region. The viscosity, gel stability and optical properties suggest that there is potential for mafafa starch applications in the food industry.

Intake of dehydrated nopal ( Opuntia ficus indica ) improves bone mineral density and calciuria in adult Mexican women

Background The intake of dehydrated nopal (DN) at a high stage of maturity along with high calcium content could improve bone mineral density (BMD) and calciuria and thus prevent osteoporosis. Objective To evaluate the effect of calcium intake from a vegetable source (DN) on BMD and calciuria covering a 2-year period in menopausal and non-menopausal women with low bone mass (LBM). Methods The study was quasi-experimental, blinded, and randomized, and included 131 Mexican women aged 35–55. Urinary calcium/creatinine index (CCI) was determined; BMD was analyzed on lumbar spine and total hip regions. Four groups were studied: Control group (CG), women with normocalciuria and a minimum dose of DN; experimental group 1 (EG1), women with hypercalciuria and a minimum dose of DN; experimental group 2 (EG2), women with hypercalciuria, and a maximum dose of DN; and normal group (NG) for reference in BMD. Results After the first semester of treatment, calciuria levels in women from both experimental groups returned to normal, remaining constant for the rest of the treatment. The percentage difference in BMD increased in the total hip region in the CG (pre 4.5% and post 2.1%) and EG2 (pre 1.8% and post 2.5%) groups significantly in comparison to NG and EG1, which exhibited a significant decrease in their BMD. BMD increased only for the lumbar region in the EG2 group (premenopausal). Conclusion The use of a vegetable calcium source such as nopal improves BMD in women with LBM in the total hip and lumbar spine regions principally in the premenopausal women, maintaining constant and normal calciuria levels.

Synthesis of Copper-Alumina Composites by Mechanical Milling: An Analysis

Copper-based composite materials are widely applied in the field of electronics and electrical engineering as highly conductive materials for operation at high temperatures. In this study, copper-based composites were produced by the powder metallurgy and reinforced with 1.0, 1.5, 2.0, 2.5, and 3.0% vol alumina nanometer sized particles. Powders were mixed by glass ball milling for 6 h at 100 rpm. Samples were compacted at 420 MPa in a steel die and sintered at 900°C for 15 min in an argon chamber. Scanning electron microscopy, X-ray diffraction, Vickers micro-hardness, and tensile tests were performed to analyze the influence of the alumina content on the mechanical, structural, and micro-structural properties of the copper-alumina composites that were manufactured by three steps of the powder metallurgy technique. X-ray diffraction patterns showed that during the ball milling, cold compacting, and sintered steps no new crystalline phases were formed. Scanning electron microscopy images providing information related to the alumina layering that restricted the reinforcement mechanism and the expected improvement in the composite mechanical properties.

Determination of the gelatinization temperature of starch presented in maize flours

A study of the influence of the moisture and the grain size on the gelatinization temperature (Tp1) of starch from four industrial maize flours as well as an unprocessed maize sample is presented. The gelatinization is a phase transition that can be observed using Differential Scanning Calorimetry (DSC), and it is manifest as an endothermic peak in the DSC thermogram. Results show that for 60, 65, 70 and 75% of moisture, the endothermic peak temperature increases from 70 to 75°C when the moisture increases, and decrease when the grain size increases from 250 to 420μm. A study of the gelatinization enthalpy (ΔHp) is also presented, this is related with the gelatinized starch present in the sample. The enthalpy decrease when the moisture increases and it decrease when grain size is increased.

Characterization of crystalline structures in Opuntia ficus-indica.

This research studies the crystalline compounds present in nopal (Opuntia ficus-indica) cladodes. The identification of the crystalline structures was performed using X-ray diffraction, scanning electron microscopy, mass spectrometry, and Fourier transform infrared spectroscopy. The crystalline structures identified were calcium carbonate (calcite) [CaCO3], calcium-magnesium bicarbonate [CaMg(CO3)2], magnesium oxide [MgO], calcium oxalate monohydrate [Ca(C2O4)•(H2O)], potassium peroxydiphosphate [K4P2O8] and potassium chloride [KCl]. The SEM images indicate that calcite crystals grow to dipyramidal, octahedral-like, prismatic, and flower-like structures; meanwhile, calcium-magnesium bicarbonate structures show rhombohedral exfoliation and calcium oxalate monohydrate is present in a drusenoid morphology. These calcium carbonate compounds have a great importance for humans because their bioavailability. This is the first report about the identification and structural analysis of calcium carbonate and calcium-magnesium bicarbonate in nopal cladodes, as well as the presence of magnesium oxide, potassium peroxydiphosphate and potassium chloride in these plants. The significance of the study of the inorganic components of these cactus plants is related with the increasing interest in the potential use of Opuntia as a raw material of products for the food, pharmaceutical, and cosmetic industries.

Differential photoacoustic cell for electrochemical and dynamic process with temperature control

A novel differential photoacoustic cell (DPC) for the study of dynamical processes has been developed. The DPC has the capability to measure in real time the amplitude and phase signals for the reference and the sample under study. The simultaneous measurement of both signals eliminates the instrumental function, and the presence of noise, due to any deviation originated by electrical, optical, and environmental factors. The DPC can be used at different temperature profiles in order to obtain the instrumental function IF(t,T). The DPC also has all the elements of an electrochemical cell capable of following the electrochemical processes. As a result of this new instrumentation it is possible to obtain in real time the amplitude and phase signals coming from the sample without any interference from the system and the viability to monitor in situ electrochemical and thermal processes. Two cases are presented as an illustrative demonstration of work fields: the electrodeposition of zinc on a steel substrate as well as the study of water and calcium ion diffusion into organic layers.

Analysis of thermal pasting profile in corn starch rich in amylose and amylopectin: Physicochemical transformations, part II.

This work focused on the study of the behaviors of the apparent viscosity profiles of isolated corn starches rich in amylose and amylopectin, through the physicochemical and morphological changes that take place during the thermal profile and the gel formation. Frozen dry samples were studied at different stages along the pasting profile. Changes in the structural properties of the samples were studied using X-ray diffraction, and the morphological changes were followed using scanning electron microscopy, differential scanning calorimetry was used to analyze the thermal changes. The changes in the pasting profile (curve of apparent viscosity) were associated with structural, thermal, and morphological changes of the starch-water suspension. From the results obtained, a new interpretation of the parameters measured with the pasting profile is introduced. In this work does not show evidence of retrogradation at the end of the cooling process for starch rich in amylopectin and that starch rich in amylose does not develop viscosity.

Thermal and Structural Characterization of Copper-Steel Bonding Interfaces Produced by Impact Welding

A complete characterization of Cu–steel impact welded were made using photothermal radiometric (PTR) spectroscopy, scanning electron microscopy (SEM), microhardness, and X-ray diffraction (XRD) in order to study the changes in the structural, metallurgical, and thermal properties of Impact Welding Zone (IWZ) and the Impact Affected Zone (IAZ) after the impact welding. Three samples with different morphological interfaces were prepared for this analysis. According to the SEM analysis in etched samples, it was possible to determine that the IWZ is formed by the collapse of grains of Cu and steel (ferrite and pearlite) into the Cu–steel interface and the IAZ are formed in a region close to the IWZ with low grain damage. Microhardness Vickers test is able to detect the IAZ in all cases, but due to its contact character, it is not possible to obtain continuous hardness information across the Cu–steel interface. According to the XRD patterns after the impact welding process, no new phase was formed. Noncontact PTR amplitude and phase images are able to identify the IAZ and the IWZ.

Effect of the alkaline and acid treatments on the physicochemical properties of corn starch

Corn starches were isolated using three different methods: water steeping, alkaline steeping, and acid steeping. The effects on their structural, micro structural, thermal, and chemical properties were evaluated, with especial emphasis in the alkaline process that is close related to the nixtamalization process. The isolation method influences the amylose content, crystallinity, and enthalpy of the starch granules. Scanning electron microscopy showed that the isolation method produced changes on the surface of the granules, and in some cases there were holes on the surface. Method 2 (the alkaline method) produces the starch granules with low protein and fat content and there was an increase in the enthalpy for this method, that can be explained in terms of thermodynamics by the increase of particles into the starch granules, which was confirmed by an increase in the ash content. A negative correlation between these variables was found (r = −0.99), while a positive correlation between enthalpy and amylose content was also found (r = 1).

Analysis of the pasting profile in corn starch: Structural, morphological, and thermal transformations, Part I.

This work is focused on the understanding of the apparent viscosity profile of corn starch, in terms of the physicochemical and morphological changes that take place during the thermal profile of starch-water suspension to its respective gel formation. A mathematical model was used to obtain the experimental operating conditions that satisfy the Froude number. Freeze drying samples are studied in different stages along the pasting profile. Changes in the structural properties of the samples are studied using X-ray diffraction, and the morphological changes are followed using scanning electron microscopy, differential scanning calorimetry was used to analyze the thermal changes in starch. The changes in the pasting profile are associated with structural, thermal,and morphological changes of the system and the analysis of the physicochemical transformation that occur during the pasting profile are explained. The finding in this work does not show evidence of gel retrogradation at the end of the cooling process.