Water molecular dynamics during bread staling by Nuclear Magnetic Resonance

Bread staling is a complex phenomenon that originates from multiple physico-chemical events (amylopectin retrogradation, water loss and redistribution) that are not yet completely elucidated. Molecular properties of white bread loaves were characterized by multiple proton Nuclear Magnetic Resonance (NMR) techniques (proton FID, T₂ and T₁ relaxation time) over 14 days of storage. Changes at a molecular level (faster decay of proton FIDs and shifting of proton T₂ relaxation times distributions towards shorter times), indicating a proton mobility reduction of the bread matrix, were observed during storage. Multiple ¹H T₂ populations were observed and tentatively associated to water-gluten and water-starch domains. Proton T₁ of bread was for the first time measured at variable frequencies (Fast Field Cycling NMR) and found to be strongly dependent upon frequency and to decrease in bread during storage, especially at frequencies ≤ 0.2 MHz. An additional proton T₁ population, relaxing at 2 ms, was detected at 0.52 MHz only at early storage times and tentatively attributed to a water-gluten domain that lost mobility during storage.     

Reference Material for the Determination of Polychlorodibenzo-<Emphasis Type="Italic">p</Emphasis>-dioxins,Polychlorodibenzo-furans,and Polychlorinated Biphenyls in Fish: Production Process,Homogeneity, and Stability

The presence of dibenzo-p-dioxins, polychlorinated dibenzofurans, and polychlorinated biphenyls in food is an important consideration for food safety, especially in fish matrices that are susceptible to bioaccumulation of those compounds from marine environments. In this context, the production of a reference material (RM) for this analytical scope is of great importance for ensuring the reliability of the results generated by monitoring programs. A lyophilized material was produced by spiking tilapia fillets with 29 compounds, and the material was evaluated based on the potential for using it as a certified reference material (CRM) or in proficiency testing (PT) schemes. A pilot experiment was performed to evaluate the incorporation of the analytes in tilapia fillets using standards prepared in nonane and in fish oil. The process yield was approximately 16% for both conditions, but higher mean recoveries were achieved with fish oil. The tilapia fillets were processed, and a portion of this bulk was spiked and then homogenized. The spiked and unspiked portions were frozen prior to lyophilization. Each freeze-dried portion was homogenized and sieved, and then, the portions were mixed, packed, and stored under refrigeration. The material was considered homogeneous for all analytes based on the criteria established for PT. Of the tested analytes, 27 were found to be stable in the short-term design (p > 0.05) when the material was kept at 45 ± 2 °C for 9 days. Long-term stability was evaluated at 2, 4, 6, and 8 months, and 22 of the analytes were found to be stable through up to 4 months of storage based on the criteria defined in references related to both the production of CRM and PT. The contributions of the homogeneity and stability in the short- and long-term uncertainties were estimated and indicated the adequacy of the material for use as a reference for trueness experiments.     

14—A SIMPLIFIED KINETIC MODEL FOR THE MECHANISM OF PILLING

A simplified kinetic model describing the mechanism of pilling is proposed. This model involves only three parameters, which relate to the main stages of the process: the total number of pills, the rate of pill formation, and the rate of pill wear-off. These parameters can easily be calculated from the pill curve of the fabric.

The published literature and the authors' own data are used to check the range of application of the proposed model.     

Oil and water determination in emulsions by pulsed low-resolution NMR

A pulsed, low-resolution nuclear magnetic resonance (NMR) technique has been used for the oil and water determination in O/W emulsions. The method is based on the analysis of the longitudinal magnetization decay curve, that, due to the different relaxation times of oil and water, consists of 2 recognizable components. Correlation of NMR results with fat content is described. A good correlation between the NMR response and fat content by weight has been found. The rapidity and accuracy of the measurements are comparable to those of other techniques.     

Integration of multiple PV units in urban power distribution systems

The amount of power and energy that can be injected into the distribution system by dispersed generation (DG) is constrained by technical issues related to electrical components rating and distribution system operation. In this context, the aim of the paper is to study the voltage profile of a LV feeder in order to assess the maximum value of the power that can be injected into multiple load points of the feeder by PV units without violating the voltage constraints.To perform this study an analytical method with integral approach is used: the distribution of generators and loads along the feeder is represented by means of continuous functions and constant current model.The main result of the proposed study is that, with reference to a set of contiguous generation units, it is possible to derive analytical relationships between the position of the point of maximum/minimum voltage on the feeder and the characteristics of the distributed generation (e.g. length of the concerned feeder portion, position of the generators and overall current injected by the generators).     

A GC-EI-MS/MS Method for the Determination of 15 Polybrominated Diphenyl Ethers (PBDEs) in Fish and Shellfish Tissues

This paper describes the development and validation of an analytical method to determine 15 polybrominated diphenyl ethers (PBDEs) in fish and shellfish tissues with gas chromatography coupled to triple quadrupole mass spectrometry using electron impact source (GC-EI-MS/MS). A QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe)-like procedure was applied; the extract was cleaned up on an acidic Extrelut-NT3 column connected on top of a silica cartridge and further purified with gel permeation chromatography (GPC). The SIM acquisition proved to yield better results than traditional MRM approach for octa-, nona-, and deca-brominated congeners. The validation study was carried out in inter-laboratory conditions. The average recoveries were in the range 66–118%, with relative standard deviations generally lower than or equal to 22%. Quality assurance and quality control practices were thoroughly described and highlighted. These long and tedious practices are fundamental to obtain reliable quantitative data during food monitoring programs and, therefore, to support daily intake assessments. Finally, the procedure was applied to the analysis of marine fish samples collected in local markets. Mackerel and mullet were the most contaminated species.     

Loss budget of a setup for measuring mechanical dissipations of silicon wafers between 300 and 4 K

A setup for measuring mechanical losses of silicon wafers has been fully characterized from room temperature to 4 K in the frequency range between 300 Hz and 4 kHz: it consists of silicon wafers with nodal suspension and capacitive and optical vibration sensors. Major contributions to mechanical losses are investigated and compared with experimental data scanning the full temperature range; in particular, losses due to the thermoelastic effect and to the wafer clamp are modeled via finite element method analysis; surface losses and gas damping are also estimated. The reproducibility of the measurements of total losses is also discussed and the setup capabilities for measuring additive losses contributed by thin films deposited on the wafers or bonding layers. For instance, assuming that additive losses are due to an 80-nm-thick wafer bond layer with Young modulus about ten times smaller than that of silicon, we achieve a sensitivity to bond losses at the level of 5x10(-3) at 4 K and at about 2 kHz.     

Study of haptoglobin-hemoglobin complexes by titration curves, capillary electrophoresis and capillary isoelectric focusing

A novel method is described for monitoring complex formation between macromolecules, based on combined isoelectric focusing-electrophoresis in capillaries. The example studied is the binding of serum haptoglobin (Hp) to hemoglobin (Hb). A known amount of Hb is focused in a capillary in a pH 6-8 range (pI of Hb = 7.0) and thus kept temporarily "immobilized" in the electrophoretic chamber. Subsequently, increasing amounts of ligand (Hp) are loaded cathodically and allowed to sweep past the focused Hb zone. As the complex formed has a pI value well-outside the bounds of such a pH gradient (the 1:1 molar Hb-Hp complex has a pI of 5.5, the 1 to 1/2 molar Hp-Hb complex has a pI of 5.0) it escapes immobilization and moves past the detector window, where it is monitored and quantified. Since the detector is set at 416 nm, where only Hb absorbs, and since the molar extinction coefficient of Hb is well known, it is quite easy to calculate the molar amount of Hb bound to the complex. As an additional check, the amount of unreacted Hb can now be mobilized by disrupting the pH gradient and allowing this residual free Hb to also reach the detector and be quantified. The method is easy, fast, simple and fully automated and thus could represent a valid alternative to existing methods in clinical chemistry for quantifying the amount of Hp in human sera in pathological conditions, such as hemolytic anemias and transfusion reactions.