Formation and decomposition of stigmasterol hydroperoxides and secondary oxidation products during thermo‐oxidation

The oxidation mechanisms of stigmasterol at 100 and 180 °C were investigated by using the HPLC‐UV‐FL method. An overall picture of the oxidation status was achieved with a single HPLC analysis, enabling us to monitor the formation and decomposition of both primary and secondary oxidation products. The oxidation behavior of stigmasterol was different at the two temperatures. At 180 °C, the amounts of hydroperoxides increased sharply during the first 10 min and then began to decrease. At 100 °C, the amounts of hydroperoxides increased over the entire experimental period. At 180 °C, all major secondary oxidation products, except 7‐ketostigmasterol, reached a plateau after 40 min of oxidation, while at 100 °C their amounts increased constantly. The same oxidation products were formed at both temperatures, but their distribution differed. At 180 °C, the formation of free radicals at position 7 was more favorable than formation of radicals at position 25. The situation was the opposite at 100 °C; radicals formed more easily at the tertiary position 25. At 180 °C, 7‐ketostigmasterol was dominant after 40 min of oxidation, whereas at 100 °C it was the main oxidation product over the entire experiment.     

A 119 GHz planar Schottky diode mixer for a space application

A planar single-ended GaAs Schottky diode mixer has been designed, built, and tested at 119 GHz. The mixer front end includes also a waveguide filter for image rejection, and a temperature compensated ring filter. Measurements at room temperature showed a conversion loss of 7 dB and a noise temperature of 900 K (SSB). At 100 K the measured noise temperature of the mixer was 500 K (SSB).     

Effects of esterification on the formation and decomposition of steryl hydroperoxides

The aim of the study was to investigate the effects of esterification on the hydroperoxide formation and decomposition of steryl ester to be able to evaluate early phases of autoxidation. In order to study hydroperoxides of intact steryl esters, a novel HPLC–ELSD method was developed. Steryl ester hydroperoxides were separated using a silica column with heptane-MBTE gradient. The method was applied to study the formation and decomposition of steryl moiety hydroperoxides in cholesteryl stearate during heating at 100 °C. To investigate the effect of esterification, also the formation of hydroperoxides in free cholesterol was measured. To confirm the results obtained by HPLC and to follow the decomposition of the hydroperoxides, peroxide values and secondary oxidation products were determined. The new HPLC showed that 7α- and 7β-OOH were the predominant hydroperoxides. In purified cholesteryl stearate, their amounts were highest (47–62 mg/g) after heating for 2–3 days, and after 4 days only small amounts were found. The formation of secondary oxidation products was marked when the amount of hydroperoxides was high. Presence of impurities in the commercial steryl ester preparation increased significantly the oxidation rate. Free cholesterol oxidised more slowly than the ester. The amount of 7-OOH epimers was only 2.6 mg/g for free cholesterol after 3 days. In conclusion, the new method was shown to be a useful tool for the determination of individual intact steryl ester hydroperoxides. The esterification of sterol affected both the rate of oxidation and the amount of formed oxidation products.     

Liquid chromatography mass spectrometry for plant sterol oxide determination in complex mixtures

Plant sterol oxidation products were determined by a sensitive liquid chromatography (LC) method with atmospheric pressure chemical ionization mass spectrometry (APCI-MS). Fragmentation of oxides was studied with stepwise fragmentation (full scan, MS², MS³) with ion trap tandem mass spectrometry. The applicability of the method was investigated using thermo-oxidized (180 °C) sterol mixture containing sitosterol, campesterol, stigmasterol and brassicasterol as a model sample. With this method, all major oxidation products of sitosterol, campesterol, stigmasterol and brassicasterol could be detected in the same run without derivatization. This LC-MS method proved to be a powerful alternative to gas chromatographic (GC) methods for the analysis of plant sterol oxides in complex mixtures and is a promising tool for future oxidation mechanism studies.     

Enzymatic hydrolysis of steryl ferulates and steryl glycosides

Steryl ferulates (SF) and steryl glycosides (SG) are phytosterol conjugates found characteristically in cereals. Currently, little is known about their properties with respect to enzymatic hydrolysis. SF and SG were extracted and purified from rye and wheat bran. Their percentages of hydrolysis with different enzymes were studied using normal phase HPLC with UV detection for steryl ferulates and evaporative light scattering detection for steryl glycosides. Steryl ferulates were hydrolysed by mammalian digestive steryl esterases. It was further demonstrated that a mixture of steryl ferulates from rye and wheat was hydrolysed much more effectively than a steryl ferulate mixture from rice (commonly known as γ-oryzanol), suggesting greater bioavailability in non-rice steryl ferulates. Steryl glycosides were hydrolysed by a commercial microbial β-glucosidase preparation (cellobiase), but were not effectively hydrolysed by two other highly purified β-glucosidases. These results demonstrate for the first time the potential use of enzymes as a replacement for acid hydrolysis in analytical procedures for SG and also provide insights about the potential bioavailability of these sterol derivatives in human digestive systems. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The importance of source configuration in quantifying footprints of regional atmospheric sulphur deposition

An atmospheric transport-chemistry model is applied to investigate the effects of source configuration in simulating regional sulphur deposition footprints from elevated point sources. Dry and wet depositions of sulphur are calculated for each of the 69 largest point sources in the UK. Deposition contributions for each point source are calculated for 2003, as well as for a 2010 emissions scenario. The 2010 emissions scenario has been chosen to simulate the Gothenburg protocol emission scenario. Point source location is found to be a major driver of the dry/wet deposition ratio for each deposition footprint, with increased precipitation scavenging of SO_x in hill areas resulting in a larger fraction of the emitted sulphur being deposited within the UK for sources located near these areas. This reduces exported transboundary pollution, but, associated with the occurrence of sensitive soils in hill areas, increases the domestic threat of soil acidification. The simulation of plume rise using individual stack parameters for each point source demonstrates a high sensitivity of SO₂ surface concentration to effective source height. This emphasises the importance of using site-specific information for each major stack, which is rarely included in regional atmospheric pollution models, due to the difficulty in obtaining the required input data. The simulations quantify how the fraction of emitted SO_x exported from the UK increases with source magnitude, effective source height and easterly location. The modelled reduction in SO_x emissions, between 2003 and 2010 resulted in a smaller fraction being exported, with the result that the reductions in SO_x deposition to the UK are less than proportionate to the emission reduction. This non-linearity is associated with a relatively larger fraction of the SO₂ being converted to sulphate aerosol for the 2010 scenario, in the presence of ammonia. The effect results in less-than-proportional UK benefits of reducing in SO₂ emissions, together with greater-than-proportional benefits in reducing export of UK SO₂ emissions.     

Sourdough derived strains of Saccharomyces cerevisiae and their potential for farmhouse ale brewing

The Finnish farmhouse ale sahti is unique in that it is fermented with baking, rather than brewing strains of Saccharomyces cerevisae. The custom of maintaining farmhouse yeast cultures is however no longer practiced in Finland, and much yeast derived diversity in sahti beers has presumably been lost as a consequence. Here, the brewing potential of a number of sourdough derived strains was tested with respect to a number of different fermentation traits. Seven strains originally isolated from Finnish or Italian sourdough cultures were used to ferment high gravity sahti wort (20°P), and fermentation performance together with production of volatile compounds were assessed and compared with a reference baking yeast. Strains differed in terms of fermentation rate, yield, yeast viability and beer flavour profile. All were maltotriose positive, but utilisation varied so that alcohol yield could be greater or lower than that of the reference strain, with values ranging from 6.6 to 7.9% (v/v). Production of aroma compounds was also variable so that it was possible to identify strains producing high levels of esters and those with lower production, which could be used to emphasise flavours originating from raw materials. All strains generated 4-vinyl guaiacol and so would be suitable for other beers where this is a part of the normal flavour profile. Results suggest that sourdough isolates of S. cerevisiae are suitable for sahti production, but could also be applied to other beer styles as a way to differentiate products. © 2020 The Authors. Journal of the Institute of Brewing published byJohn Wiley & Sons Ltd on behalf of The Institute of Brewing & Distilling     

Fate of hormones and pharmaceuticals during combined anaerobic treatment and nitrogen removal by partial nitritation-anammox in vacuum collected black water

Vacuum collected black (toilet) water contains hormones and pharmaceuticals in relatively high concentrations (μg/L to mg/L range) and separate specific treatment has the potential of minimizing their discharge to surface waters. In this study, the fate of estrogens (natural and synthetical hormones) and pharmaceuticals (paracetamol, metoprolol, propranolol, cetirizine, doxycycline, tetracycline, ciprofloxacin, trimethoprim, carbamazepine, ibuprofen and diclofenac) in the anaerobic treatment of vacuum collected black water followed by nitrogen removal by partial nitritation-anammox was investigated. A new analytical method was developed to detect the presence of several compounds in the complex matrix of concentrated black water. Detected concentrations in black water ranged from 1.1 μg/L for carbamazepine to >1000 μg/L for paracetamol. Anaerobic treatment was only suitable to remove the majority of paracetamol (>90%). Metoprolol was partly removed (67%) during aerobic treatment. Deconjugation could have affected the removal efficiency of ibuprofen as concentrations even increased during anaerobic treatment and only after the anammox treatment 77% of ibuprofen was removed. The presence of persistent micro-pollutants (diclofenac, carbamazepine and cetirizine), which are not susceptible for biodegradation, makes the application of advanced physical and chemical treatment unavoidable.     

Separation and isolation of β-sitosterol oxides and their non-mutagenic potential in the Salmonella microsome assay

The recent increase in phytosterol-enriched functional food provokes questions concerning the safety of their oxidation products. However, most of the existing toxicity studies have been performed with mixtures instead of single compounds, a consequence of the lack of pure phytosterol oxidation product (POP)-standards.