Pyrrolizidine alkaloids in food: downstream contamination in the food chain caused by honey and pollen

In recent years, there has been a steadily growing number of published data on pyrrolizidine alkaloids (PAs) in honey and pollen. This raises the question whether honey and/or pollen used as ingredients in food processing might provoke a downstream contamination in the food chain. Here we addressed two different facets in connection with PAs in honey and pollen. First, we analysed the PA content of several food types such as mead (n = 19), candy (n = 10), fennel honey (n = 9), soft drinks (n = 5), power bars and cereals (n = 7), jelly babies (n = 3), baby food (n = 3), supplements (n = 3) and fruit sauce (n = 1) that contained honey as an ingredient in the range of 5% to approximately 37%. Eight out of 60 retail samples were tested as being PA-positive, corresponding to 13%. Positive samples were found in mead, candy and fennel honey, and the average PA content was calculated to be 0.10 μg g(-1) retronecine equivalents (ranging from 0.010 to 0.484 μg g(-1)). Furthermore, we investigated the question whether and how PAs from PA pollen are transferred from pollen into honey. We conducted model experiments with floral pollen of Senecio vernalis and PA free honey and tested the influence of the quantity of PA pollen, contact time and a simulated honey filtration on the final PA content of honey. It could clearly be demonstrated that the PA content of honey was directly proportional to the amount of PA pollen in honey and that the transfer of PAs from pollen to honey was a rather quick process. Consequently, PA pollen represents a major source for the observed PA content in honey. On the other hand, a good portion remains in the pollen. This fraction is not detected by the common analytical methods, but will be ingested, and it represents an unknown amount of 'hidden' PAs. In addition, the results showed that a technically and legally possible honey filtration (including the removal of all pollen) would not be an option to reduce the PA level of the final product significantly.     

Comparing problem formulations for coupled sets of components

This paper presents several formulations and comparative test results for problems involving the general paradigm of coupled sets of components (CSoC). This paradigm is general enough to include systems of systems (SoS) under any of the various definitions, as well as multidisciplinary design optimization (MDO). It is assumed that a CSoC involves a (potentially inactive) coordinating component, or “Central Authority”, and one or more, potentially interacting, subordinate components. The formulations differ in the amount of control given to the CA versus the autonomy granted to the subordinate components. In this generality, satisfaction of equilibrium conditions replaces the optimality condition in defining a solution. A solution still requires feasibility of all constraints. The desirability of a particular equilibrium point depends on the specific problem being studied and the component algorithms used to obtain that equilibrium. These concepts are illustrated using comparative test results for several of the formulations on a NASA-generated, public domain, aircraft conceptual design problem.     

Reductive dechlorination of 1,1,2,2-tetrachloroethane

Products of the transformation of organic pollutants in the environment are often predicted based on the structure of the parent compounds. In some cases, however, multiple products may result from the same reaction pathway. In this study, the reduction of 1,1,2,2-tetrachloroethane (1,1,2,2-TeCA) is investigated both experimentally and computationally. Experimental results and data available in the literature reveal that the ratio of Z-1,2-dichloroethylene (Z-DCE) to E-1,2-dichloroethylene (E-DCE) produced from the reductive beta-elimination of 1,1,2,2-TeCA is approximately 2:1, and this ratio is independent of the reductant used. The exception is iron metal, which results in a ratio of 4.5:1. Computational results reveal that the 1,2,2-trichloroethyl radicals (1,1,2-TCA*) formed upon the transfer of the first electron are nearly isoenergetic and are in rapid equilibrium. Thus, the conformer population of the 1,1,2,2-TeCA does not dictate the product distribution. Using Marcus theory, it is demonstrated that the Z:E ratio of 2:1 reflects the relative rates of the two possible electron transfer steps to the two radical conformers. Further analysis of the thermochemistry of the reaction reveals that this ratio of rate constants should be essentially independent of the thermodynamic driving force, which is consistent with the experimental results. The different observed product distribution when iron metal is the reductant is hypothesized to result from an organometallic intermediate. The reduction of the 1,1,2,2-TeCA is an overall two-electron process, but the fact that the radicals equilibrate at a rate more rapid than the transfer of the second electron suggests that reductants employed act as decoupled single electron-transfer agents.     

X-ray Raman spectroscopy of carbon in asphaltene: light element characterization with bulk sensitivity

X-ray Raman spectra of the carbon K-edge have been recorded using 6.461 keV radiation for a petroleum asphaltene. By comparison with coronene, graphite, and paraffin standards, the asphaltene spectrum is seen to be composed of contributions from saturated and aromatic carbon species. The information contained in the carbon K-edge was extracted with bulk (approximately 1 mm) sensitivity, because the Raman method used hard X-rays. This helps alleviate concerns about surface artifacts that frequently occur with soft X-ray spectroscopy of light elements. X-ray Raman spectroscopy shows great potential for characterization of light elements in fuels, catalysts, and other complex materials under chemically relevant conditions.     

Microstructure and properties of a composite system for dental applications composed of glass-ceramics in the SiO2–Li2O–ZrO2–P2O5 system and ZrO2-ceramic (TZP)

The objective of the study was to develop a biocompatible composite system which was composed of TZP-ceramic (tetragonal zirconia polycrystals, ZrO₂ stabilized with 3 mol% Y₂O₃) and two glass-ceramics of the SiO₂–Li₂O–ZrO₂–P₂O₅ type. The metal-free composite system would satisfy the translucency, the biocompatibility and the strength requirements of dentistry. The two glass-ceramics of the SiO₂–Li₂O–ZrO₂–P₂O₅ type with a content of 15 and 20 wt% ZrO₂ respectively, were chemically and physically adapted to TZP-ceramic. The glass-ceramics were used as a dentin buildup material. The TZP-ceramic had the function of a root post. The shape of the post was cylindrical with a conical tip. The composite system was easy to process through viscous flow of the glass-ceramic at 900 and 1000°C, respectively. The microstructure and the mechanical properties of two glass-ceramics of the SiO₂–Li₂O–ZrO₂–P₂O₅ type were examined therefore.     

Stoichiometrically bound beta-carotene in the cytochrome b6f complex of oxygenic photosynthesis protects against oxygen damage

The cytochrome b6f complex of oxygenic photosynthesis carries out "dark reactions" of electron transfer that link the light-driven reactions of the reaction centers, and coupled proton transfer that generates part of the electrochemical potential utilized for ATP synthesis. In contrast to the bc1 complex of the respiratory chain, with which there are many structural and functional homologies, the b6f complex contains bound pigment molecules. Along with the specifically bound chlorophyll a previously found to be bound stoichiometrically in the dimeric b6f complex, it was found in the present study that beta-carotene is also present in the b6f complex at stoichiometric levels or nearly so. Chlorophyll and carotenoid pigments were quantitatively extracted from b6f complex purified from (i) the thermophilic cyanobacterium, Mastigocladus laminosus, (ii) spinach chloroplasts, and (iii) the green alga, Chlamydomonas reinhardtii. Visible and mass spectra showed the carotenoid to be a beta-carotene of molecular weight = 536, with a stoichiometry of 1. 0:1 relative to cytochrome f in the highly active M. laminosus complex but somewhat lower stoichiometries, 0.77 and 0.55, in the b6f complex obtained from spinach chloroplasts and C. reinhardtii. A photoprotective function for the beta-carotene was inferred from the findings that the rate of photobleaching of the chlorophyll a bound in the complex was found to vary inversely with beta-carotene content and to decrease markedly in the presence of ambient N2 instead of air. The presence of beta-carotene in the b6f complex, and not in the related bc1 complexes of the mitochondrial respiratory chain and photosynthetic bacteria, suggests that an additional function is to protect the protein complexes in oxygenic photosynthetic membranes against toxic effects of intramembrane singlet O2.