Fatty acid methyl and ethyl esters as well as wax esters for evaluating the quality of olive oils

A promising correlation between chemical analysis and sensorial evaluation was confirmed: extra virgin olive oils with low contents of methyl and ethyl esters of fatty acids as well as straight chain wax esters were sensorially evaluated as being of high quality, whereas some with high contents were even devaluated as not being of extra virgin quality. Methanol and ethanol formed during fermentation in degrading olives are esterified, largely by transesterification with fatty acids from the triglycerides, and in this way transferred into the pressed oil. The presence of high contents of methyl and ethyl esters in degrading olives was confirmed. Wax esters from the skin of the olives are extracted at low yields, whereby the yield increases when the olives are soft and possibly degrading. High wax ester contents may, therefore, stand for mild oils, but also for deficient oils.     

XRCT characterisation of Ti particles inside porous Al2O3

Computed X-ray tomography was used to characterise distribution and sphericity of Ti granules within highly porous (> 35%) Al₂O₃ powder compacts, as they are key parameters for a successful infiltration by Fe-based alloys. Setting of reconstruction constraints, image editing as well as data processing are the most challenging parts of computed X-ray tomography and principal sources of errors that bias the generated data. Thus, corrective measures have to be applied and the reliability of generated data has to be proved with respect to statistical, stereological and volumetric aspects. Combining an adapted Interface Particle Treatment Algorithm with the Marching Cube Method, Equilibrium Random State Model, cluster splitting and conventional laser diffraction measurements a significant improvement of the three-dimensional reconstructed data was achieved. This study points out the need of the applied algorithms for the proof and improvement of generated data by computed X-ray tomography and gives a short survey of methods that can be applied.     

Dynamics of an intruder in dense granular fluids

We investigate the dynamics of an intruder pulled by a constant force in a dense two-dimensional granular fluid by means of event-driven molecular dynamics simulations. In a first step, we show how a propagating momentum front develops and compactifies the system when reflected by the boundaries. To be closer to recent experiments (Candelier and Dauchot in Phys Rev 81(1):011304, 2010; Phys Rev 103(12):128001, 2009), we then add a frictional force acting on each particle, proportional to the particle’s velocity. We show how to implement frictional motion in an event-driven simulation. This allows us to carry out extensive numerical simulations aiming at the dependence of the intruder’s velocity on packing fraction and pulling force. We identify a linear relation for small and a nonlinear regime for high pulling forces and investigate the dependence of these regimes on granular temperature.     

Update on recycled paperboard and its compliance for food contact

The last 3 years brought much movement around the migration from recycled paperboard in general and of mineral oil in particular. It has been shown that it is unrealistic to ensure the safety of the many and variable migrants from recycled fibers. The toxicological evaluation of mineral oil remains uncertain, but the strong accumulation of certain saturated mineral hydrocarbons in human tissues might increase the concern. The draft of a German regulation on mineral oil migration from recycled paper and board struggles with the difficult analysis in food, but frequent measurement in food is avoidable if the compliance work can be based on citable systematic studies. In the discussions about potential solutions, the introduction of barriers prevails. Internal bags with barrier layers have been widely introduced. For packings without internal bags, barriers on the internal surface of the recycled paperboard have been developed, but not yet introduced into the market on broad scale. An agreed method for measuring barrier efficiency and a specification of minimum required efficiency are probably a prerequisite. Work for an industry standard on barriers is on-going in Switzerland.     

Barriers against the Migration of Mineral Oil from Paperboard Food Packaging: Experimental Determination of Breakthrough Periods

A method is described for determining the breakthrough periods through various types of potential functional barriers. A donor pack with a sheet of paper containing the test migrant(s) was tightly fixed to one side of the barrier. It included a blank sheet of paper as a spacer to rule out wetting contact between the donor and the barrier. A polyethylene film acted as a receptor on the other side. Periodically, a piece of the receptor film was analysed for the test migrants broken through the barrier. As benchmarks, periods were extrapolated for 1% and 10% breakthrough compared with equilibration. Tests were performed at 60°C, 40°C and ambient temperature. Acceleration by increased temperature gave reasonably adequate results for polyethylene but too short breakthrough periods for polypropylene, owing to structural changes in the polymer. The donor pack also included Sudan red 2, which is of sufficient volatility to migrate through the gas phase. It enabled visual control for gaps and holes in the barrier layers or cracks, e.g. from manipulation (such as bends or scratches), by red spots in the tested material behind the barrier or in the receptor film. Breakthrough data for mineral oil of the type typically used in cold‐set offset printing inks are provided for a selection of materials. Polyethylene terephthalate and polyamide showed no breakthrough for a period corresponding to 6.9 years. Copyright © 2011 John Wiley & Sons, Ltd.     

Three‐dimensional pore structure and ion conductivity of porous ceramic diaphragms

The ion conductivity of two series of porous ceramic diaphragms impregnated with caustic potash was investigated by electrochemical impedance spectroscopy. To understand the impact of the pore structure on ion conductivity, the three‐dimensional (3‐D) pore geometry of the diaphragms was characterized with synchrotron x‐ray absorption tomography. Ion migration was calculated based on an extended pore structure model, which includes the electrolyte conductivity and geometric pore parameters, for example, tortuosity (τ) and constriction factor (β), but no fitting parameters. The calculated ion conductivities are in agreement with the data obtained from electrochemical measurements on the diaphragms. The geometric tortuosity was found to be nearly independent of porosity. Pore path constrictions diminish with increasing porosity. The lower constrictivity provides more pore space that can effectively be used for mass transport. Direct measurements from tomographs of tortuosity and constrictivity opens new possibilities to study pore structures and transport properties of porous materials.     

Structure of the mosquitocidal delta-endotoxin CytB from Bacillus thuringiensis sp. kyushuensis and implications for membrane pore formation

The delta-endotoxin CytB, found in parasporal inclusions of Bacillus thuringiensis subspecies kyushuensis, is a membrane pore-forming protein which is lethal to the larvae of Dipteran insects and broadly cytolytic in vitro. The crystal structure of CytB in the protoxin form has been determined by isomorphous replacement using heavy-atom derivatives of both the wild-type protein and an engineered cysteine mutant. The atomic model comprising residues 19 to 245 and 28 bound water molecules has been refined at 2.6 angstrom resolution to a crystallographic R-factor of 19.7% and a free R-factor of 26.1%. CytB has a single domain of alpha/beta architecture but a novel connectivity comprising two outer layers of alpha-helix hairpins wrapped around a mixed beta-sheet. In the protoxin form, CytB is a dimer linked by the intertwined N-terminal strands in a continuous, 12-stranded beta-sheet. Proteolytic processing cleaves the intertwined beta-strands to release the active CytB as a monomer, as well as removing the C-terminal tail to uncover the three-layered core. The homologous toxin CytA should show the same fold. Mutations in CytA that inhibit expression map to the dimer contacts and to the tip of helix pair A-B in contact with the sheet, apparently preventing correct folding. Mutations that inhibit toxicity map to the edge of the beta-sheet adjoining the helix pair C-D and to the sheet face, while mutations on the helix surfaces have no effect. Therefore segments forming the sheet, rather than the amphiphilic but short helices, are responsible for membrane binding and pore formation. A conformational change is postulated by which the helix pair C-D peels away from the sheet to lie on the membrane surface, while the sheet region rearranges to form an oligomeric trans-membrane pore.     

Levels of HIV-infected peripheral blood cells remain stable throughout the natural history of HIV-1 infection. Swiss HIV Cohort Study

OBJECTIVE: To clarify the relationship between the number of provirus-bearing peripheral blood mononuclear cells (PBMC) and HIV-1 disease progression during the natural history of infection. DESIGN: Twenty-four HIV-1-infected subjects with known seroconversion dates and long-term follow-up were retrospectively identified using the Swiss HIV Cohort Database. PBMC specimens from this cohort were retrieved from storage for analysis. METHODS: Infected PBMC equivalents were determined by HIV-1 DNA quantitative competitive (QC)-PCR. The results were analysed with respect to HIV-1 disease stage and compared with a mathematical model of long-term HIV-1 disease progression. RESULTS: PBMC HIV-1 DNA did not correlate with major indices of disease progression, including time following primary infection, time before reaching a CD4 cell count less than 200 x 10(6)/l, and time before death. The number of PBMC harbouring HIV-1 provirus was relatively constant throughout the clinical stages of HIV-1 infection, consistent with simulated data from a mathematical model of long-term HIV-1 infection. We also showed that a biased interpretation of the QC-PCR data may arise when the values are expressed as HIV-1 DNA copies per PBMC or per CD4 cell. CONCLUSIONS: This analysis suggests that levels of provirus-bearing PBMC remain constant during the natural course of HIV-1 infection, whereas plasma virus load typically increases logarithmically during the same period. The hypothesis that plasma virus levels are directly related to the number of infected cells may deserve reconsideration.     

Relative hopane content confirming the mineral origin of hydrocarbons contaminating foods and human milk

Hopanes, triterpenoid hydrocarbons formed under geological conditions, were analysed to confirm the mineral origin of the unresolved complex mixtures of hydrocarbons observed in the gas chromatography with flame ionization detection chromatograms of human milk and certain foodstuffs. The 'relative hopane content' (RHC) is introduced, i.e. it is the area ratio of the sum of the hopanes and the paraffins in the same segment of the chromatogram. The RHC in various mineral oil products (motor oils, hydraulic oils, lubricating oils, Vaseline) was 3.4%, with a relative standard deviation of 19%. The RHC determined in samples of vegetable oils, mussels and clams as well as of human milk containing an unresolved complex mixture of hydrocarbons was in the same range, confirming that these samples were contaminated by mineral oil material.