Characterization of galactooligosaccharides derived from lactulose

Galactooligosaccharides are non-digestible carbohydrates with potential ability to modulate selectively the intestinal microbiota. In this work, a detailed characterization of oligosaccharides obtained by transgalactosylation reactions of the prebiotic lactulose, by using β-galactosidases of different fungal origin (Aspergillus oryzae, Aspergillus aculeatus and Kluveromyces lactis), is reported. Oligosaccharides of degree of polymerization (DP) up to 6 were detected and quantified by HPLC-ESI MS from a complex mixture produced by transgalactosylation reaction with A. oryzae (GOSLuAo), whereas only carbohydrates up to DP4 and DP5 were found for those obtained from the reaction with β-galactosidases from K. lactis (GOSLuKl) and A. aculeatus (GOSLuAa), respectively. Disaccharides (galactosyl-galactoses and galactosyl-fructoses) and trisaccharides were characterised in the three mixtures by GC-MS as their trimethylsilyl oximes. Galactosyl- and digalactosyl-glycerols were produced during the transgalactosylation reaction of lactulose with β-galactosidases from A. aculeatus and K. lactis, due to the presence of glycerol as enzyme stabiliser.     

Harmonic generation in ablation plasmas of wide bandgap semiconductors

Third and fifth harmonic generation of an IR (1.064 μm) pulsed laser has been produced in ablation plasmas of the wide bandgap semiconductors CdS and ZnS. The study of the temporal behaviour of the harmonic emission has revealed the presence of distinct compositional populations in these complex plasmas. Species ranging from atoms to nanometre-sized particles have been identified as emitters, and their nonlinear optical properties can be studied separately due to strongly differing temporal behaviour. At short distances from the target (<1 mm), atomic species are mostly responsible for harmonic generation at early times (<500 ns), while clusters and nanoaggregates mostly contribute at longer times (>1 μs). Harmonic generation thus emerges as a powerful and universal technique for ablation plasma diagnosis and as a tool to determine the nonlinear optical susceptibility of ejected clusters or nanoparticles.     

Industriall Control of the Filtration in the Beer Manufacturing Process

In the aim to improve the filtration process in the beer ma nufacture, a study on the beer turbidity have been made using two different techniques: nephelometry and V-UV spectrometry. Even though the former is the most commonly used, we propose the use of V-UV spectrometry since it is possible to follow the performace - of all the filtration line, not only in a punctual way but in a - wide range of wavelenghts. From the results of this work we deduce that V-UV spectrometry offers a better quality of results than nephelometry, being more useful in rutin periodic controls.     

Effects of high pressure on unsaturated fatty acids

The objective of this study is to investigate the effects of high pressure processing on the molecular structure of some unsaturated fatty acids. Samples of elaidic acid, linoleic acid, ZE and EE conjugated linoleic acid are treated at 293 or 333?K at pressures up to 700?MPa. It is observed that the adiabatic heat generated from compression is able to bring the sample temperature above 373?K after 700?MPa. These relatively extreme conditions are of great interest for food sterilization, but they may induce undesirable change in fatty acid quality characteristics. To check for structural changes, Raman spectra of the samples are analysed after treatments. The comparison with Raman spectra of samples kept at atmospheric pressure shows that pressure induces some conformational changes at the hydrocarbon skeleton in solid samples, while the liquid ones remain unchanged. No cis/trans isomerization occurs, but gauche conformers are likely to be present.     

Compositional changes induced by 3.5 keV Ar ion bombardment in Ni-Ti oxide systems A comparative study

Compositional changes induced by 3.5 keV Ar⁺ sputtering in TiO₂, NiO, NiTiO₃ and a (TiO₂ + NiO) mixture have been quantitatively studied by XPS. Although all the samples show important changes in their stoichiometry, the extent of the decomposition depends on the compound. The stability of Ti⁴⁺ appears to be enhanced by the presence of Nisu2+ cations which, on the other hand, are more easily reduced to Ni⁰ than in pure NiO. To explain these results a redox solid state reaction between the intermediate phases formed during sputtering is proposed, which tends to preserve the most stable phases.     

Guided modes of integrated optical guides. A mathematical study

A waveguide in integrated optics is defined by its refractiveindex. The guide is assumed to be invariant in the propagationdirection while in the transverse direction it is supposed tobe a compact perturbation of an unbounded stratified medium.We are interested in the modes guided by this device, whichare waves with a transverse energy confined in a neighbourhoodof the perturbation. Our goal is to analyse the existence of such guided modes. Underthe assumptions of weak guidance the problem reduces to a two-dimensionaleigenvalue problem for a scalar field. The associated operatoris unbounded, selfadjoint, and bounded from below. Its spectrumconsists of the discrete spectrum corresponding to the guidedmodes and of the essential spectrum corresponding to the radiationmodes. We present existence results of guided modes and an asymptoticstudy at high frequencies, which shows that contrarily to thecase of optical fibers, the number of guided modes can remainbounded. The major tools are the min-max principle and comparisonof results between different eigenvalue problems. The originalityof the present study lies in the stratified character of theunbounded reference medium.     

Structure of the products of condensation of hydroxylamine with trifluoromethyl-beta-diketones: assignments of the diastereotopic protons of the 4-methylene group in 5-hydroxy-5-trifluoromethyl-delta2-isoxazolines

The combined use of 1H NMR spectroscopy with theoretical calculations of chemical shifts (GIAO) and coupling constants (B3LYP/6-311 ++G**) of a 5-hydroxy-5-trifluoromethyl-Delta2-isoxazoline has enabled solving the problem of the assignments of the diastereotopic protons in this compound. This result has been extended to 5-hydroxy-5-trifluoromethyl-Delta2-pyrazolines and the corresponding 5-trichloromethyl derivatives.     

Rapid evaluation of surface sanitation by electrical measurement

Electrical measurements are easier and faster than traditional methods for evaluating surface sanitation in the food industry. However, the behavior of sublethally damaged bacteria is different in each method. The electrical method is more sensitive to the presence of disinfectant traces in the samples. These issues lead to low correlations between both methods (r2 < 0.7). The use of smaller sample volumes in electrical measurements, together with the addition of a blend of neutralizers to the sample and the subsequent removal by filtration, provide r2 values > 0.9. The developed protocol shows an excellent correlation with traditional methods and facilitates the adaptation of the electrical method to routine monitoring of surface sanitation. It allows for a reduction in holding times and thereby provides the necessary time to make decisions.