Enzymatic production of human milk fat substitutes containing palmitic and docosahexaenoic acids at sn-2 position and oleic acid at sn-1,3 positions

This paper studies the synthesis of structured triacylglycerols (STAGs) rich in palmitic and docosahexaenoic acids (PA and DHA) at sn-2 position and oleic acid (OA) at sn-1,3 positions by a four step process. First, triacylglycerols (TAGs) were obtained with 63–66 mol PA/100 mol total fatty acids and 10 mol DHA/100 mol by acidolysis of tuna oil and commercial PA, catalyzed by the non-positionally specific lipase Novozym 435. Then these TAGs were purified neutralizing the free fatty acids (FFAs) by KOH hydroethanolic solutions and extracting TAGs with hexane; these TAGs were completely recovered as pure TAGs (without FFAs). The third step involved the displacement of fatty acids located at sn-1,3 positions by acidolysis of PA and DHA enriched TAGs with OA rich FFAs, catalyzed by the sn-1,3 specific lipase DF from Rhizopus oryzae, immobilized on Accurel MP-1000; TAGs with 67 mol OA/100 mol at sn-1,3 positions and 52.1 and 15.4 mol PA and DHA, respectively, per 100 mol at sn-2 position were obtained. Both acidolysis reactions were carried out in stirred tank reactors (STRs) with lipase both dispersed in the reaction medium and contained in a cartridge filter attached to the stirrer rod. Finally STAGs were purified and obtained with yields of over 80 mol STAGs/100 mol STAGs in the reaction product (no FFAs were detected).     

Bio-hydrogen production during acidogenic fermentation in a multistage stirred tank reactor

The objective of this study was to evaluate the production of hydrogen in a two-stage CSTR system – both reactors having the same volume – and compare its performance with a conventional one-stage process. The lab-scale two-stage and one-stage systems were operated at five pHs and five hydraulic retention time (HRTs). The maximum volumetric hydrogen productivity and yield obtained with the two-stage system were 5.8 mmol L⁻¹ h⁻¹ and 2.7 mol H₂ mol glucose⁻¹, respectively, at an HRT of 12 h and pH 5.5. Overall, the two-stage system showed, at steady state, a better performance that the one-stage system for all the evaluated pHs. However, a comparison between the one-stage system, operating at 6 h of HRT, and the first reactor of the two-stage system at the same HRT did not show any significant difference, highlighting the positive impact of having a two-stage process. The determination of the ratio between the experimental measured H₂ in the gas phase and the theoretical H₂ generated in the liquid phase (discrepancy factor) indicated that an important part of the hydrogen produced in the first reactor was transferred into the second reactor instead of being desorbed in the headspace. Therefore, the improving of hydrogen production in the two-stage system is rather attributed to the increased transfer of hydrogen from liquid to gas than an actual total hydrogen production increase.     

Rational spatio-temporal strategies for controlling a Chagas disease vector in urban environments

The rational design of interventions is critical to controlling communicable diseases, especially in urban environments. In the case of the Chagas disease vector Triatoma infestans, successful control is stymied by the return of the insect after the effectiveness of the insecticide wanes. Here, we adapt a genetic algorithm, originally developed for the travelling salesman problem, to improve the spatio-temporal design of insecticide campaigns against T. infestans, in a complex urban environment. We find a strategy that reduces the expected instances of vector return 34-fold compared with the current strategy of sequential insecticide application to spatially contiguous communities. The relative success of alternative control strategies depends upon the duration of the effectiveness of the insecticide, and it shows chaotic fluctuations in response to unforeseen delays in a control campaign. We use simplified models to analyse the outcomes of qualitatively different spatio-temporal strategies. Our results provide a detailed procedure to improve control efforts for an urban Chagas disease vector, as well as general guidelines for improving the design of interventions against other disease agents in complex environments.     

School location methodology in urban areas of developing countries

This study is concerned with the location of primary public schools. The public system should have the capacity to satisfy all the demand, although students may choose between public and private schools if they can afford the corresponding costs. A number of factors, such as questionable education quality, limited capacity, poor location and social preferences, secure a participation of about 30% to the private school system. The purpose of this study is both the evaluation of the existing public school network and a relocation proposal. The result of the former was the identification of areas with shortage and excess in school offer. The latter suggests school relocation using capacitated and uncapacitated models. ArcView, a software of the geographic information system (GIS) family, was employed, allowing the efficient handling of large problems and improving the presentation and evaluation of the findings. This methodology was applied to the primary public school network in the area of Vitoria, a state capital located in the southeast region of Brazil with about 300,000 inhabitants. Finally, the practical use of this study and its importance for planning purposes are discussed.     

Effect of the extraction and bleaching processes on jojoba (Simmondsia chinensis) wax quality

The aim of the work was to evaluate the effect of extraction method and bleaching on the quality of jojoba waxes from Argentina. Jojoba waxes obtained by cold pressing, Golden wax (expeller‐pressed wax) and Lite wax (bleached wax) were analyzed using standard methods adopted as recommended practices by the American Oil Chemists Society. Physical parameters, fatty acid and alcohol compositions were unchanged among waxes. Cold‐pressed wax was noteworthy by its lower peroxide value, higher amounts of tocopherol and total phenol contents. Accordingly, it presented the best oxidative stability. Bleaching caused a strong decrease in both tocopherol and phenol contents; consequently the bleached wax showed poor oxidative stability.     

Isolation and Structural Elucidation of Antiproliferative Compounds of Lipidic Fractions from White Shrimp Muscle (Litopenaeus vannamei)

Shrimp is one of the most popular seafood items worldwide, and has been reported as a source of chemopreventive compounds. In this study, shrimp lipids were separated by solvent partition and further fractionated by semi-preparative RP-HPLC and finally by open column chromatography in order to obtain isolated antiproliferative compounds. Antiproliferative activity was assessed by inhibition of M12.C3.F6 murine cell growth using the MTT (3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide) assay. The methanolic fraction showed the highest antiproliferative activity; this fraction was separated into 15 different sub-fractions (M1–M15). Fractions M8, M9, M10, M12, and M13 were antiproliferative at 100 µg/mL and they were further tested at lower concentrations. Fractions M12 and M13 exerted the highest growth inhibition with an IC₅₀ of 19.5 ± 8.6 and 34.9 ± 7.3 µg/mL, respectively. Fraction M12 was further fractionated in three sub-fractions M12a, M12b, and M12c. Fraction M12a was identified as di-ethyl-hexyl-phthalate, fraction M12b as a triglyceride substituted by at least two fatty acids (predominantly oleic acid accompanied with eicosapentaenoic acid) and fraction M12c as another triglyceride substituted with eicosapentaenoic acid and saturated fatty acids. Bioactive triglyceride contained in M12c exerted the highest antiproliferative activity with an IC₅₀ of 11.33 ± 5.6 µg/mL. Biological activity in shrimp had been previously attributed to astaxanthin; this study demonstrated that polyunsaturated fatty acids are the main compounds responsible for antiproliferative activity.     

Combined Mutagenesis and Kinetics Characterization of the Bilin‐Binding GAF Domain of the Protein Slr1393 from the Cyanobacterium Synechocystis PCC6803

The gene slr1393 from Synechocystis sp. PCC6803 encodes a protein composed of three GAF domains, a PAS domain, and a histidine kinase domain. GAF3 is the sole domain able to bind phycocyanobilin (PCB) as chromophore and to accomplish photochemistry: switching between a red‐absorbing parental and a green‐absorbing photoproduct state (λ_max=649 and 536 nm, respectively). Conversions in both directions were followed by time‐resolved absorption spectroscopy with the separately expressed GAF3 domain of Slr1393. Global fit analysis of the recorded absorbance changes yielded three lifetimes (3.2 μs, 390 μs, and 1.5 ms) for the red‐to‐green conversion, and 1.2 μs, 340 μs, and 1 ms for the green‐to‐red conversion. In addition to the wild‐type (WT) protein, 24 mutated proteins were studied spectroscopically. The design of these site‐directed mutations was based on sequence alignments with related proteins and by employing the crystal structure of AnPixJg2 (PDB ID: 3W2Z), a Slr1393 orthologous from Anabaena sp. PCC7120. The structure of AnPixJg2 was also used as template for model building, thus confirming the strong structural similarity between the proteins, and for identifying amino acids to target for mutagenesis. Only amino acids in close proximity to the chromophore were exchanged, as these were considered likely to have an impact on the spectral and dynamic properties. Three groups of mutants were found: some showed absorption features similar to the WT protein, a second group showed modified absorbance properties, and the third group had lost the ability to bind the chromophore. The most unexpected result was obtained for the exchange at residue 532 (N532Y). In vivo assembly yielded a red‐absorbing, WT‐like protein. Irradiation, however, not only converted it into the green‐absorbing form, but also produced a 660 nm, further‐red‐shifted absorbance band. This photoproduct was fully reversible to the parental form upon green light irradiation.     

Ageing of V2O5 thin films induced by Li intercalation multi-cycling

Cyclic voltammetry, XPS, RBS and AFM have been combined to study the ageing mechanism of Li intercalation in V₂O₅ thin films prepared by thermal oxidation of vanadium metal. Multi-cycling tests were performed in 1 M LiClO₄-PC in the potential range E ∈ [3.8, 2.8 V] versus Li/Li⁺, corresponding to the α-to-δ phase transition. XPS and AFM were performed using direct anaerobic and anhydrous transfer. Capacity fading remains inferior to 20% during ∼2500 cycles. XPS shows slight modifications of the oxide composition with a V⁴⁺ concentration increasing from ∼5% prior to cycling to ∼16–27% after cycling, due to Li trapped in the oxide film and to the loss of V₂O₅ active material. The presence of lithium carbonate and lithium-alkyl carbonate species evidences the formation of the so-called SEI layer. AFM evidences the loss of crystalline material by grain exfoliation from the outer V₂O₅ layer of the oxide film. By further exfoliation, the inner VO₂ layer of the oxide film is reached and pits are formed, occupying ∼9–13% of the surface. This de-cohesion at grain boundaries is attributed to the strain generated by repeated lattice distortions. After 3300 cycles, the disappearance of lithium carbonates, whereas Li-alkyl carbonates and/or Li-alkoxides remain on the surface, indicates the dissolution and/or conversion of the SEI layer. After 4500 cycles, the oxide film became very labile and could be stripped away by rinsing to reveal the vanadium metal substrate.