Hexabromocyclododecane enantiomers: microsomal degradation and patterns of hydroxylated metabolites

The degradation of the enantiomers of α-, β-, and γ-hexabromocyclododecane (HBCD) by phase I metabolism was investigated using induced rat liver microsomes. HBCD isomers were quantified using HPLC-MS/MS (ESI(-)) after separation on a combination of a reversed phase and a chiral analytical column. The degradation of all six isomers followed first-order kinetics and the estimated half-lives ranged from 6.3 min for both β-HBCD enantiomers to 32.3 min in case of (+)-γ-HBCD. (+)-α- and (-)-γ-HBCD displayed significantly shorter half-lives than their corresponding antipodes. It could be shown that this degradation led to a significant enrichment of the first eluting enantiomers (-)-α- and (+)-γ-HBCD. Individual patterns of mono- and dihydroxylated derivatives obtained from each α- and γ-HBCD enantiomer were seen to be distinctly characteristic. The patterns of monohydroxylated HBCD derivatives detected in liver and muscle tissues of pollack, mackerel and in herring gull eggs were largely similar to those observed in the in vitro experiments with rat liver microsomes. This enabled individual hydroxy-HBCDs to be assigned to their respective parent HBCD enantiomers.     

Preparation of immobilized Trametes pubescens laccase on a cryogel-type polymeric carrier and application of the biocatalyst to apple juice phenolic compounds oxidation

A new biocatalyst was prepared by the immobilization of a Trametes pubescens laccase, into a wide-pore poly(vinyl alcohol) cryogel. The known enzyme was produced and purified by the previously described procedure. The resulted laccase (yield 40%) has an activity of 46.4 U mg⁻¹ and 12.51 mg mL⁻¹ protein content. The enzyme was subsequently immobilized in a functionalized macroporous cryogel beads by a covalent immobilization technique. The time dependence of the immobilization process and the enzyme loading of the carrier material (5.2 mg g⁻¹ cryogel) were determined by measuring the decrease of protein amount in the enzyme solution. In conversion experiments, a higher stability of the immobilized biocatalyst compared to the free enzyme was evidenced. Steady-state kinetic characterization of four phenols (catechol, caffeic and chlorogenic acids, and catechin) has been performed with free and immobilized laccase, the catalytic parameters being determined and compared. The effect of both laccases (free and immobilized) on the phenol content of retailed apple juice samples, having the same initial composition, was also investigated by working in batch conversion. The variation in phenolic compound content has been compared with that of an untreated apple juice sample having initially the same content of phenolic compounds. A number of advantages resulted in using the immobilized laccase for the apple juice treatment (conservation to some extent of enzyme activity, higher content of phenols preserved, easy separation of the enzyme from the apple juice, therefore avoiding the possible unhealthy effects due to the remaining protein, etc.).     

Dietary exposure assessment of putrescine and cadaverine and derivation of tolerable levels in selected foods consumed in Austria

Biogenic amines (histamine, tyramine, putrescine, cadaverine, agmatine, spermidine and spermine) are nitrogenous compounds. They occur naturally in living organisms and are involved in many biological processes. Nonetheless, high amounts in food may be hazardous to human health. The diamines putrescine and cadaverine in food can potentiate the effects of simultaneously ingested histamine. In protein-rich foods, high concentrations of these diamines are indicative for hygienic deficiencies in the food chain. Even though being formed endogenously and being essential for some physiological metabolic pathways, both diamines are known as precursors for carcinogenic nitrosamines. Putrescine also plays a certain role in tumour growth. Nevertheless, no tolerable levels in foods have been established so far. The present study suggests tolerable levels in cheese, fermented sausages, fish, sauerkraut and seasonings that are based on toxicological threshold levels, occurrence of diamines in foods and food consumption in Austria. Average daily intake of putrescine via fermented food was calculated to be 6.8 (female adults) and 8.8 (male adults) mg per person. Respective numbers for cadaverine were 9.8 and 11.6 mg per person and day. For putrescine, proposed maximum tolerable levels for sauerkraut, fish, cheese, fermented sausages and seasonings are 140, 170, 180, 360 and 510 mg/kg, respectively. Likewise, for cadaverine, in sauerkraut, fish, cheese, fermented sausages and seasonings, maximum tolerable levels are 430, 510, 540, 1,080 and 1,540 mg/kg, respectively. These limits can be met by current manufacturing practices, as ascertained from the results of our own studies and from literature. Admittedly, only few data are published on toxicological threshold levels of these diamines, which mean that these tolerable levels are associated with some uncertainty.     

The \delta{}^{18}{\rm O} -value of the p-OH group of L-tyrosine permits the assignment of its origin to plant or animal sources

The biosynthesis of L-tyrosine in plants by the shikimate pathway via arogenate implies that the oxygen atom in the p-position originates from D-erythrose with a d¹⁸O \delta{}^{18}{\rm O} -value near +30‰ above leaf water, while its synthesis in animals by hydroxylation of external L-phenylalanine with O₂ as oxygen source and a kinetic isotope effect k₁₆/k₁₈ɏ.018 demands a d¹⁸O \delta{}^{18}{\rm O} -value near +6‰. These expectations are fully confirmed by experimental data from the ¹⁸O-pattern analysis of natural aromatic compounds. The result is considered as a basis for the assignment of L-tyrosine and L-tyrosine-derived material of plant or animal origin, respectively, and for the determination of the relative amounts of plant and animal material in food and animal feed.     

Polychlorinated biphenyl compounds in milk and dairy products

Summary The PCB content of 469 milk and dairy product samples was determined. The fat was extracted and cleaned up through aluminium oxide. The organochlorine pesticides and the PCBs were separated by chromatography through a silica gel column. The PCBs in the purified extracts were perchlorinated to decachlorobiphenyl and determined by gas chromatography. The mean PCB content of the samples investigated was 0.18 mg per kg fat. The results are comparable with those obtained in neighbouring countries and significantly lower than the interim FDA tolerance of 1.5 mg per kg fat.

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Polychlorierte Biphenylverbindungen in Milch und Milcherzeugnissen

Zusammenfassung Der Gehalt an polychlorierten Biphenylverbindungen wurde in 469 Milch- und Milcherzeugnis-Proben bestimmt. Das Fett wurde extrahiert und über Aluminiumoxid gereinigt. Die Organochlorpesticide und die PCB's wurden durch Chromatographie über eine Silicagelkolonne getrennt. Die PCB's der gereinigten Extrakte wurden zu Dekachlorbiphenyl perchloriert und durch Gaschromatographie bestimmt. Der durchschnittliche PCB-Gehalt der gesamten Muster betrug 0,18 mg pro kg Fett. Die Ergebnisse können mit denen der Nachbarländer verglichen werden und sind bedeutsam niedriger als die vorläufige FDA-Toleranz von 1,5 mg pro kg Fett.

     

Microstructural changes in m. rectus abdominis bovine muscle after heating

A histological and ultrastructural study was conducted to characterize changes in beef muscle structure after heating. Pieces of rectus abdominis muscle were heated at 100 °C over varying time frames from 15 min to 60 min and at 270 °C for 1 min; samples were then prepared for optical and transmission electron microscopy. After 15 min of heating, at 100 °C, a lateral shrinkage in fibre of 48% and an increase in gaps between the myofibrillar masses of 27% was noted. No more significant evolution was observed as heating duration escalated. The ultrastructure showed strong myofibril to sarcolemma detachments in which granular aggregates, coming in part from myofibrillar proteins, are stored. Neighbouring muscle fibres showed strong heterogeneity in morphological behaviour after thermal treatment, suggesting that differences in composition and structure of the cytoskeleton proteins in the different fibres can cause denaturation/shrinkage of the proteins at different times along the timescale of microstructural changes during heating. Short heating at high temperatures expanded the gaps between myofibrillar mass, but the overall changes in the ultrastructure were similar to those obtained when heating at 100 °C.     

Assessing forest fire as a potential PCDD/F source in Queensland, Australia

Forest fires are suggested as a potential and significant source of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs), even though no studies to date provide sufficient evidence to confirm forest fires as a source of PCDD/Fs. Recent investigations in Queensland, Australia have identified a widespread contamination of PCDDs (in particular OCDD) in soils and sediments in the coastal region from an unknown source of PCDD/Fs. Queensland is predominately rural; it has few known anthropogenic sources of PCDD/Fs, whereas forest fires are a frequent occurrence. This study was conducted to assess forest fires as a potential source of the unknown PCDD/F contamination in Queensland. A combustion experiment was designed to assess the overall mass of PCDD/Fs before and after a simulated forest fire. The results from this study did not identify an increase in sigmaPCDD/Fs or OCDD after the combustion process. However, specific non-2,3,7,8 substituted lower chlorinated PCDD/Fs were elevated after the combustion process, suggesting formation from a precursor. The results from this study indicate that forest fires are unlikely to be the source of the unknown PCDD contamination in Queensland, rather they are a key mechanism for the redistribution of PCDD/Fs from existing sources and precursors.     

Beef sausage structure affected by sodium chloride and potassium lactate

A histological and ultrastructural study was conducted to characterize changes in the muscle fibre structure of three fresh sausage preparations, depending on meat composition, sodium chloride (NaCl) and potassium lactate (K-lactate) contents. After addition of 0.8% and 1.6% NaCl, 65% and 51%, respectively, of the area observed showed well preserved fibres (histological data). The altered regions presented a large disorganization of the myofilaments and a solubilization of the sarcolemma and of the Z lines. K-lactate addition had no marked effects on meat structure. The preparation containing some sheep meat was more sensitive to salt than the others containing only bovine meat. The level of alteration was much lower than those obtained in pork meat in another study. Technological conditions used to modify the internal muscle fibre structure during sausage processing depend on the species used. Therefore, the classification of the sausage preparation to “meat preparation” or “meat product” under the EU regulation (EC) No. 853/2004 (which assign meat preparations to meat if the product has undergone a process insufficient to modify the internal muscle fibre structure of the meat) must be systematically controlled when changing the meat sausage composition.