Determination of aldehydes in tequila by high-performance liquid chromatography with 2,4-dinitrophenylhydrazine derivatization

In this work, the determination of aldehydes in different tequila brands was carried out by high-performance liquid chromatography after derivatization with 2,4-dinitrophenylhydrazine. For the comparative purposes, two commercial brandies were also analyzed. The derivatization agent (50 μl of 3.5 mmol l⁻¹ DNPH in HCl, 2 mol l⁻¹) was added directly to the sample (500 μl) and dinitrophenylhydrazones formed were extracted with hexane. After evaporation of the solvent in nitrogen stream, the residues were dissolved in 100 μl of acetonitrile. The calibration standards were prepared from respective dinitrophenylhydrazones, following the same procedure as for beverage samples. Reversed phase chromatographic separation was achieved on Luna C18 column (250 mm×4.6 mm, 5 μm), using gradient elution (acetonitrile:water, from 68 to 80% of acetonitrile in 20 min) and a total flow rate 1 ml min⁻¹. Spectrophotometric detection for furanic aldehydes was at 390 nm (for other aldehydes at 365 nm). The assignation of chromatographic peaks was accomplished by comparison of their relative retention times and UV/Vis spectra with those of external standards. The method of standard addition was also used. The aldehydes identified were 5-hydroxymethylfurfuraldehyde (t _ret=4.1 min), formaldehyde (t _ret=5.1 min), syringaldehyde (t _ret=5.6 min), acetaldehyde (t _ret=6.2 min), 2-furaldehyde (t _ret=7.2 min) and 5-methylfurfuraldehyde (t _ret=8.9 min). At least four chromatographic peaks with retention times higher than 12 min remained unidentified. The quantification results showed drastically higher concentrations of 2-furaldehyde and 5-methylfuraldehyde in tequilas as referred to brandies. Furthermore, 100% tequilas contained higher levels of these two compounds (for four brands analyzed, mean values 18.6 and 5.97 μg ml⁻¹, respectively) as compared to the mixed brands (five brands analyzed, mean values 6.46 and 3.30 μg ml⁻¹). The results obtained confirm that the profile of furanic aldehydes depends on the type of fructans contained in the raw material and also on heating treatment applied or not prior to fermentation. In contrast to other polysaccharides, inulin hydrolyzes at elevated temperature and the contribution of Maillard browning reactions increases the production of furanic compounds. Our results indicate that the levels of 2-furaldehyde and 5-methylfuraldehyde could be used for discrimination between 100% and mixed tequila brands.     

Influence of ferrous iron incorporation on the structure of hydroxyapatite

Iron is a vital element of cellular function within the body. High concentrations of iron can be found in the kidneys and the circulatory system. In bones and teeth it is present as a trace element. The use of iron-based compounds in combination with hydroxyapatite offers a new alternative for prosthetic devices. This work investigates the synthesis and processing of iron containing apatites as a possible new type of ceramic for biomedical devices. Stoichiometric and calcium deficient iron containing apatites were synthesized by a wet chemical reaction with di-ammonium-hydrogen-phosphate, calcium nitrate and a ferrous iron nitrate solution. A secondary phase of tri-calcium-phosphate (TCP) was observed after heat treatment of iron containing, calcium deficient, hydroxyapatite. The apatite structure was maintained after heat treatment of stoichiometric apatite, synthesized in the presence of iron. Sintering in air produced oxidation of Fe²⁺ to Fe³⁺, resulting in the formation of hematite as a secondary phase. The introduction of iron into the synthesis of hydroxyapatite causes: (i) an increase of the a-lattice parameter after synthesis and heat treatment in air; (ii) an increase in the c-lattice parameter after sintering in air.     

Extracts of Haematoxylon brasiletto inhibit growth, verotoxin production, and adhesion of enterohemorrhagic Escherichia coli O157:H7 to HeLa cells

The extracts of 33 plants were evaluated for their effects on growth of Escherichia coli O157:H7 (EHEC). The extract of Haematoxylon brasiletto was the only one that effectively inhibited bacterial growth. The effects of ethanolic extracts of this plant on growth, verotoxin production, and adhesion of E. coli O157:H7 to HeLa cells were determined. The MBC for growth was 4 mg/ml. No verotoxin formation was detected at 1, 2, or 3 mg/ml. Preexposing bacteria and HeLa cells to various concentrations of extracts affected the adhesion between non-EHEC and HeLa cells. Partial purification of the active fraction suggested that polyphenols might play a role in the antimicrobial activity exhibited by H. brasiletto extracts.     

Consequences of the development of nisin-resistant Listeria monocytogenes in fermented dairy products

Wild Listeria isolates representing serovars found in artisanal cheeses commercialized in Asturias (northern Spain) were assessed for their susceptibility to several bacteriocins. Pediocin PA-1 was the most active bacteriocin followed by enterocin AS-48, nisin, and plantaricin C. However, some Listeria monocytogenes and Listeria innocua strains were already highly resistant to PA-1. Among the wild L. monocytogenes populations, the frequency of development of nisin resistance ranged from 10(-6) up to 10(-3), depending on the strain. Highly stable mutants with increased nisin resistance (two- to fourfold) were isolated and tested for potential cross-resistance to lysozyme, EDTA, and various NaCl concentrations and pH values. All mutants were cross-resistant to lysozyme but sensitive to EDTA. In contrast, no clear correlation could be established between nisin resistance and an altered susceptibility to NaCl or pH changes. Nisin-resistant variants were able to survive and even to multiply in milk fermented by a nisin-producing Lactococcus, but the growth of the wild-type strain was inhibited. The different phenotypes evaluated in this study are indicative of the unpredictability of the consequences of the development of nisin resistance in a dairy environment. This resistance should be considered when making a risk assessment of the long-term use of nisin to control L. monocytogenes.     

The Influence of electrochemical surface modifications on naval steel corrosion

The corrosion behaviour of naval steels is characterized by cyclic voltammetric profiles, open-circuit potential decays and polarization curves in 0.5 M sodium nitrate and in 0.6 M sodium chloride at 20 °C. Naval steel surfaces can be modified by the application of periodic symmetric and/or asymmetric potential routines in strong alkaline solutions. These perturbations produce the formation of protective or non-protective surface oxides, which can be characterized by scanning electron microscopy and cyclic voltammetry. Corrosion parameters of the new surface oxides are evaluated by polarization curves after long-time exposures in electrolytes containing sodium chloride and sodium nitrate.     

Synthesis of N-heteroaryl retinals and their artificial bacteriorhodopsins

N-Heteroaryl retinals derived from indole, 1-indolizine and 3-indolizine (10 a-c) have been synthesized after their UV/Vis red-shifted absorption properties had been predicted by time-dependent density functional theory (TD-DFT) computations. The three new analogues form artificial pigments upon recombination with bacterioopsin: indolyl retinal 10 a undergoes fast and efficient reconstitution to form a species with a UV/Vis absorbance maximum similar to that of wild-type bacteriorhodopsin, whilst the indolizinyl retinals 10 b and 10 c also reconstitute in significant proportion to give noticeably red-shifted, although unstable, pigments. Significant changes in the pK(a) values of these artificial bacteriorhodopsins are interpreted as arising from nonoptimal binding-site occupancy by the chromophore due to steric constraints.     

Studies on the solution conformation and dynamics of a polysaccharide from Sinorhizobium fredii HH103 and its monosaccharide repeating unit

The conformational behavior of the homopolysaccharide isolated from Sinorhizobium fredii HH103 and its monosaccharide repeating unit (5-acetamido-3,5,7,9-tetradeoxy-7-(3-hydroxybutyramido)-L-glycero- L- manno-nonulosonic acid) was analyzed by nuclear magnetic resonance (NMR) spectroscopy and extensive molecular dynamics simulations (MD). The results indicate that the glycosidic linkages and lateral chains may adopt a variety of conformations. MD simulations using the generalized Born solvent-accessible surface area (GB/SA) continuum solvent model for water and the MM3* force field provide a population distribution of conformers that satisfactorily agrees with the experimental NMR data for the torsional degrees of freedom of the molecule.     

Behavioral evaluation of the unilateral lesion model in rats using 6-hydroxydopamine. Correlation between the rotations induced by D-amphetamine, apomorphine and the manual dexterity test

INTRODUCTION: Evaluation of rotatory activity induced by dopaminergic agonists is the most widely used test of conduct for the measurement of dopaminergic depletion of a unilateral lesion of the striatonigral pathway caused by 6-hydroxydopamine (6-OHDA) in rats, since it is quantitatively related to the extension of the dopaminergic denervation. OBJECTIVE: The objective of this study was to evaluate, from different angles, the changes in conduct seen in the model of unilateral lesion with 6-OHDA and to establish correlation with the rotation induced by D-amphetamine and by apomorphine and the ladder test. MATERIAL AND METHODS: Male Wistar rats were used. Lesions were produced in the SNpc by stereotactic injection of 6-OHDA into the right hemisphere and the effectiveness of the lesions was studied using the rotary conduct induced by D-amphetamine and apomorphine. The motor ability of the front legs was measured by the ladder test, carried out under standard and forced conditions. RESULTS: All the animals with lesions had difficulty in reaching food with both legs, although the most pronounced deficit was in the leg contralateral to the lesion. The ladder test correlated better with rotatory activity induced by apomorphine than by D-amphetamine. CONCLUSION: The animals with most dopamine loss showed most deficient use of their front legs.     

Indicators of oxidative stress in aging rat brain. The effect of nerve growth factor

INTRODUCTION AND OBJECTIVE: Increased oxidative stress during ageing and the neurodegenerative disorders associated with this has been described. The central nervous system is particularly vulnerable to oxidative damage because of its high energy requirements, high oxygen consumption, high tissue concentration of iron and relatively low levels of some antioxidant systems. Treatment with neurotrophic factors may reverse neurone deterioration and stimulate cholinergic activity in aged rats. It may have a similar neuroprotector effect against damage due to ischaemic reperfusion, hypoglycaemia, inflammation and other pathological conditions involving oxidative stress. In this study we determined some indicators of oxidative stress in rat brains during ageing and evaluated this in response to a plan of treatment with murine nerve growth factor (FCN) for 38 days. MATERIAL AND METHODS: Biochemical techniques were used for determination of oxidative stress indicators. RESULTS AND CONCLUSIONS: We found that with age there was a significant increase in phospholipase A2 and superoxide dysmutase activity and concentration of hipoperoxidases, whilst the concentration of reduced glutathion fell. Catalase activity increased in the hippocampal and striate regions and decreased in the cortex and septal area. There was less oxidative stress in rats treated with FCN. In view of our results, we conclude that the level of oxidative stress increases with ageing, with significant differences between areas of the brain. The region most vulnerable to damage from species reactive to oxygen was the hippocampus, and the protective effect of FCN may be related to potentiation of antioxidant defenses.