Total content and dialyzable iron and zinc in foods from northern and Southern Mexico

Developing countries diets are based on a variety of plant foods that often are the main suppliers of important amounts of iron (Fe) and zinc (Zn). The objectives of this study were 1) to measure the total and dialyzable amounts of Fe and Zn in foods from Northern Mexico (Sonora) and from Southern Mexico (Oaxaca) and 2) to evaluate the effect of meat content of diets on the dialyzable amount of Fe and Zn. Methods to calculate the total dialyzable amount of Fe and Zn, were those of the AOAC and of Shen et al. Total Fe in e northern Mexican foods went from 0.78 +/- 0.0 to 11.59 +/- to 0.03 mg/ 100g (dry weight, DW); in southern Mexican foods the same micronutrient amounts were 0.86 +/- 0.18 to 8.8 +/- 0.57 mg/100 g (BS). Total Zn values were 0.91 +/- 0.00 to 13.58 +/- 0.05 mg/100 g (DW) in Sonora, and 0.64 +/- 0.18 to 20.80 +/- 0.33 mg/100 g (DW) in Oaxaca. In northern Mexico, foods dialyzable Fe had values from 0.1 +/- 0.04% to 10.6 +/- 0.36% and for Zn from 4.0 +/- 0.21% to 55.32 +/- 0.14%. Meanwhile, the range of values of dialyzable Fe for foods from Oaxaca were from 0.22 +/- 0.06% to 9.40 +/- 0.14% for and from 2.41 +/- 0.26% to 54.27 +/- 1.49% for dialyzable Zn. The average value for dialyzable Fe was higher in the foods that contained meat or meat products (p= 0.001).     

Guar gum methyl ethers. Part I. Synthesis and macromolecular characterization

Guar gum (GG) has been partially methyl-etherified under heterogeneous reaction conditions. The resulting products, (methyl ether guar: MG) with different degrees of substitution, have been characterized by means of viscosity, ¹H NMR, and FTIR measurements. The introduction of methoxyl groups along the polysaccharidic chains reduces the hydrogen bonding sites on the guar backbone reducing primarely the extent of hydrogen bonding between guar macromolecules, hence their aggregation tendency. A comparative analysis of Mark–Houwink–Sakurada parameters and of the characteristic ratio (C_∞) of GG and MG samples in aqueous solution has been carried out using the Burchard–Stockmayer–Fixman method for flexible and semiflexible chains. The MG chains exhibit more flexibility than those of native guar gum which is traceable to a disruption of intrachain hydrogen bonds.     

Liquid-liquid extraction of protease from cold-adapted yeast Rhodotorula mucilaginosa L7 using biocompatible and biodegradable aqueous two-phase systems

This work aimed to optimize the extraction of an extracellular protease produced by the cold-adapted yeast Rhodotorula mucilaginosa L7 using aqueous two-phase systems (ATPS) comprising polyethylene glycol (PEG) and sodium citrate or sodium tartrate. First, the biocompatibility of the phase forming agents was assessed. The results obtained with PEG-2000, PEG-4000, and PEG-6000 demonstrated that even at large PEG concentrations (32 wt%) the protease maintains its activity after 3 h of reaction, whereas an increase in salt concentration provokes a gradual decrease in protease stability. Subsequently, the partitioning of the protease in both types of ATPS was assessed, evaluating the effect of temperature, molecular weight, and concentration of PEG on protease purification, using two 2³-full factorial designs. The best partitioning conditions were obtained in PEG-6000/sodium tartrate-based ATPS, at 30ºC (with a yield of 81.09 ± 0.66% and a purification factor of 2.51 ± 0.03). Thus, considering the biodegradable characteristics of the system, the PEG/sodium tartrate ATPS is a viable and economic low-resolution step in protease purification, with a strong potential for future industrial application.     

Wear resistance glass-ceramics with a gahnite phase obtained in CaO-MgO-ZnO-Al2O3-B2O3-SiO2 system

The thermal conditions for obtaining the glass-ceramic material of Al_0.107B_0.374Mg_0.043Zn_0.282Ca_0.100Si_0.927O₃ with a crystalline phase in the form of gahnite (ZnAl₂O₄) were specified. The activation energy E_a and the Avrami parameter n for the crystallisation process were determined with the non-isothermal DTA procedure. The maximum temperatures of crystallisation of phases, depending on the rate of heating, ranged between 800-840 °C for willemite and 870-915 °C for gahnite. The homogeneous crystalline spinel phase was obtained by heat treatment above 1000 °C. Precipitation solely of a ghanite phase from glass-ceramic causes a relative increase in its fracture toughness and wear resistance compared to the two-phase materials, i.e., K_IC = 2.12-1.65 MPam^1/2 and w_s = 0.21 × 10⁻⁴ mm³/Nm to w_s = 1.43 × 10⁻⁴ mm³/Nm.     

Chain packing versus chain mobility in semialiphatic BTDA-based copolyimides

A series of partially aliphatic copolyimides derived from 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), 4,4′-diaminodiphenylmethane (DDM) and 1,6-diaminohexane (DAH) was synthesized. Solubility tests and structural characteristics, evaluated by wide-angle X-ray diffraction measurements (WAXD) did not vary steadily with the content of the flexible segment. On the dynamic mechanical analysis (DMA) the evolution of the secondary relaxations (γ and β) suggested an increased chain tightness as more aliphatic component is included. The onset temperature of α-relaxation decreased regularly with the content of aliphatic sequence. During the α-relaxation the trend of E′, E″ and tan δ with temperature, and at multiple frequencies, evidenced the overlapping of phenomena. The increased mobility determines the formation of oriented structures that behave as constraints. Simultaneously, as the flexible content (DAH segment) is more important, orientation relaxations take place with increasing temperature. The equilibrium between stiffening and flowing makes the polyimides with high aliphatic content behave like elastomers.     

Chemical modification of chloromethylated polysulfones via click reactions

A new approach to the modification of azidomethyl polyethersulfones using click reactions with acetylenic derivatives in the presence of CuBr as catalyst is presented. An azidomethyl polyethersulfone was prepared by the reaction of chloromethylated polysulfone with sodium azide in dimethylformamide. By the Cu(I)‐catalysed Huisgen 1,3‐dipolar cycloaddition reaction of the azidomethyl polyethersulfone to acetylenic derivatives, new polyethersulfones containing 1,2,3‐triazole rings were obtained. The structures of the polymers were confirmed using attenuated total reflectance Fourier transform infrared and NMR spectroscopy. The polymers were characterized using dynamic mechanical analysis, thermogravimetric analysis, stress‐strain and water contact angle measurements and solubility tests. The polymers bearing 1,2,3‐triazole rings having OH or COOH as substituents exhibited static contact angles smaller than that of the parent polyethersulfone. Copyright © 2010 Society of Chemical Industry