A Reale

NMR metabolic profiling of organic and aqueous sea bass extracts: Implications in the discrimination of wild and cultured sea bass

The nuclear magnetic resonance (NMR) technique was used as analytical tool to determine the complete metabolic profiling of sea bass extracts: water-soluble metabolites belonging to different classes such as sugars, amino acids, dipeptides and organic acids as well as metabolites soluble in organic solvent such as lipids, sterols and fatty acids were identified. The metabolite profiling together with a suitable statistical analysis were used to discriminate between wild and cultured sea bass samples. Preliminary results show that discrimination between wild and cultured sea bass was obtained not only using fatty acid composition but also cholesterol and phosphatidylethanolamine and some water-soluble metabolites such as choline, trimethylamine oxide, glutamine, fumaric and malic acids.

Presence of yeasts in southern Italian sourdoughs from Triticum aestivum flour

Samples of sourdoughs obtained from 13 artisanal bakeries located in the Molise and Campania regions were analysed. The sourdoughs were produced with the exclusive use of Triticum aestivum wheat flour. pH values of sourdoughs from Molise were generally lower than those from Campania. The number of yeasts in the samples of sourdoughs from Molise was generally higher than in those from Campania, which in two cases evidenced counts about 2 log cfu x g(-1). By utilising and comparing traditional and biomolecular techniques of identification a complete picture of the isolates was obtained: 58 strains were identified as Saccharomyces cerevisiae, five as Candida colliculosa, four as C. lambica, three as C. krusei, three as C. valida and two as C. glabrata.

Experimental validation of GaN HEMTs thermal management by using photocurrent measurements

A major limitation in the performances of AlGaN/GaN high-electron mobility transistors (HEMTs) is due to self heating effects, connected to the efficiency of heat removal from the device. In this paper, we present a new experimental investigation on the thermal handling capabilities of AlGaN/GaN HEMTs, with conventional and flip-chip bonding. Efficient photocurrent measurements were performed in order to extract directly the channel temperature for all the device configurations. We were able to measure devices realized on sapphire substrate both with conventional and flip-chip bonding, and to compare them with devices on SiC substrate with conventional bonding, demonstrating that flip-chip bonding allows to achieve almost the same results that SiC substrate. Measured results are in good agreement with the presented simulation data.

Gain dynamics in traveling-wave semiconductor optical amplifiers

A theoretical analysis of the optical properties of multiquantum well semiconductor optical amplifiers (MQW-SOA) have been performed in the time-dependent regime. We describe the interaction between pulse propagation and gain compression within a pump-probe excitation in polarization insensitive MQW-SOA. We use a phenomenological model based on rate equations (describing the carrier dynamics in the different heterolayers along the growth axis for both bulk and MQW structures), coupled with the description of picosecond optical pulse propagation within a semiconductor slab (along the active waveguide axis), to describe the way gain dynamics determine the optical response of the SOA. Our model agrees well with available experimental data and also reveals the conditions for the validity of previous simpler approaches.

Interactions between Lactobacillus sakei and CNC (Staphylococcus xylosus and Kocuria varians) and their influence on proteolytic activity

Aims:  To evaluate interactions between Lactobacillus sakei and coagulase negative cocci (CNC) (Staphylococcus xylosus and Kocuria varians) and to investigate the influence of these interactions on their own proteolytic activity.

Interactions between strains of Staphylococcus xylosus and Kocuria varians isolated from fermented meats

Aims:  To evaluate the interactions of Staphylococcus xylosus on Kocuria varians strains isolated from fermented meat products.

Study of gain compression mechanisms in multiple-quantum-well In/sub 1-x/Ga/sub x/As semiconductor optical amplifiers

A combined experimental and theoretical analysis of the dynamical properties of multiple-quantum-well semiconductor optical amplifiers is presented. In particular, a polarization-independent optical amplifier has been realized using a tensile barrier InGaAs-InGaAs quantum-well active layer. The dynamics of gain recovery after optical pumping have been measured and the results have been interpreted in the light of a rate-equation analysis.

Irradiation Treatments to Improve the Shelf Life of Fresh Black Truffles (Truffles Preservation by Gamma-Rays)

The aim of this study was to individuate a method to improve the shelf life of fresh truffles, hypogeous fungi highly prized but very perishable as well. Microbial ecology of fresh products was investigated and the effect of irradiation at different doses on microbial and sensorial parameters was assayed. Data showed that fresh truffles are strongly contaminated from different groups of microorganisms. Irradiation was able to influence their growth, determining an impressive reduction. Treatments at 5 and 10 kGy doses produced the highest microbial decontamination but negatively influenced sensorial parameters. Irradiation at a 1.5 kGy dose was the best solution to improve the shelf life of truffles.

Microbiological and fermentative properties of baker's yeast starter used in breadmaking.

This study assessed the levels of microbial contaminants in liquid, compressed and dry commercial bakers yeasts used as starters in breadmaking. Eumycetes, Enterobacteriaceae, total and fecal coliforms, Bacillus spp., and lactic acid bacteria (LAB), in particular enterococci, were quantified. Results obtained in this study highlighted that bakers yeast could represent a potential vehicle of spoilage and undesirable microorganisms into the baking environment, even if these do not influence the leavening activity in the dough, as ascertained by rheofermentometer analysis. Different microbial groups, such as spore-forming bacteria and moulds, were found in bakers yeast starters. Moreover, different species of LAB, which are considered the main contaminants in large-scale yeast fermentations, were isolated and identified by Denaturing Gradient Gel Electrophoresis (DGGE) and 16S rDNA sequencing. The most recurrent species were Lactobacillus plantarum, Enterococcus faecalis, and Enterococcus durans, isolated from both compressed and dry starters, whereas strains belonging to Leuconostoc and Pediococcus genera were found only in dry ones. Nested-Polymerase Chain Reaction (Nested-PCR) and Randomly Amplified Polymorphic DNA-PCR (RAPD-PCR) were also used to highlight the biodiversity of the different commercial yeast strains, and to ascertain the culture purity.

Shelf Life of Fresh Sausages Stored under Modified Atmospheres

The aim of this study was to investigate differences in modified atmosphere packaging (MAP) for the improvement of the shelf life of fresh meat products. Three different conditions for preserving fresh sausages were tested: MAP1 (20% CO2, 70% O2, and 10% N2), MAP2 (40% CO2 and 60% O2), and MAP3 (40% CO2, 30% O2, and 30% N2). Samples from the MAP2 group had fewer spoilage bacteria, stable red color (no change of a* value), and good physical attributes (high water-holding capacity, little loss from cooking, and low shear force needed for cutting) compared with samples from other treatment groups. Thus, high concentrations of CO2 (40%) and O2 (60%) resulted in a longer shelf life for fresh sausages.