Human bitterness detection thresholds of hop acids in beer and honey

Alpha acids are found in the lupulin glands of hops cones. These acids have no bitterness of their own, but can be isomerized and subsequently hydrogenated to form bitter iso-α-acids and tetrahydroiso-α-acids respectively. Current literature values for the detection thresholds of iso-α-acid and tetrahydroiso-α-acid in lager beer have been reported using American Society of Testing and Materials (ASTM) method 679, a method commonly used to find detection thresholds of various compounds. ASTM method 679 is currently described as a “rapid method” and was a forerunner to ASTM method 1432, the current standard method for finding human detection thresholds. It has been argued that ASTM method 679 is statistically weaker than ASTM method 1432, as a group threshold found using ASTM method 679 is based on an individual “best estimate threshold” found using only one ascending series of 3-altrnative forced choice (3-AFC) presentations per panelist. The group threshold found using ASTM method 1432 is based on individual thresholds that are determined using data from 6 ascending series of 3-AFC presentations per panelist, the principle being that test repetition will help nullify moment-to-moment panelist variation. However, test repetition takes time, and the lack of repetition required for ASTM method 679 makes the method quicker and simpler to implement than ASTM method 1432. Current literature detection threshold values for both iso-α-acids and tetrahydroiso-α-acids in lager beer have not been found using ASTM method 1432. The primary objective of the research presented in this paper was to use the current ASTM standard method to determine updated threshold values for both iso-α-acids and tetrahydroiso-α-acids in lager beer. The secondary objective of this research was to compare threshold results from the same data set using ASTM method 679 and ASTM method 1432 to evaluate whether these methods provide statistically similar results. Findings showed that implementation of ASTM method 679 to find individual thresholds did produce results that were not statistically different from individual results found using ASTM method 1432. All group thresholds except the Day 1 tetrahydroiso-α-acid threshold found using ASTM 679 were also statistically in agreement with group thresholds obtained using ASTM method 1432. Beta acids, like alpha acids, are found in the lupulin glands of hops cones. Beta acids oxidize to form bitter compounds. Beta acids and tetrahydroiso-α-acids have been found to be miticidal against varroa mites, parasitic mites that feed off of and damage honeybees and bee larva. Though beta acids and tetrahydroiso-α-acids are FDA-declared GRAS substances, and will have no ill-effects on honey consumers, bees may transfer the bitter acids to their honey. Detectable levels of these bitter substances could lead to consumer rejection of honey from hives treated with beta acids or tetrahydroiso-α-acids. In a second experiment discussed in this thesis, the detection thresholds of beta acids and tetrahydroiso-α-acids were found in light clover honey. A method for the extraction and quantification of beta acids and tetrahydroiso-α-acids in beer and wort was modified and verified for the extraction and quantification of hops acids in honey. This method combined with group threshold data obtained in this experiment can be used in an industrial setting to determine whether the concentrations of beta acids and/or tetrahydro-iso-α-acids that may have been transferred to honey are above or below the human detection threshold.Keywords: Hops, Honey, Beer, Threshol

Improved performance of the LHCb Outer Tracker in LHC Run 2

The LHCb Outer Tracker is a gaseous detector covering an area of $5\times 6 m^2$ with 12 double layers of straw tubes. The performance of the detector is presented based on data of the LHC Run 2 running period from 2015 and 2016. Occupancies and operational experience for data collected in $p p$, pPb and PbPb collisions are described. An updated study of the ageing effects is presented showing no signs of gain deterioration or other radiation damage effects. In addition several improvements with respect to LHC Run 1 data taking are introduced. A novel real-time calibration of the time-alignment of the detector and the alignment of the single monolayers composing detector modules are presented, improving the drift-time and position resolution of the detector by 20\%. Finally, a potential use of the improved resolution for the timing of charged tracks is described, showing the possibility to identify low-momentum hadrons with their time-of-flight.Comment: 29 pages, 20 figures, minor changes to match the published versio

Transcriptome signatures of wastewater effluent exposure in larval zebrafish vary with seasonal mixture composition in an effluent-dominated stream

Wastewater treatment plant (WWTP) effluent-dominated streams provide critical habitat for aquatic and terrestrial organisms but also continually expose them to complex mixtures of pharmaceuticals that can potentially impair growth, behavior, and reproduction. Currently, few biomarkers are available that relate to pharmaceutical-specific mechanisms of action. In the experiment reported in this paper, zebrafish (Danio rerio) embryos at two developmental stages were exposed to water samples from three sampling sites (0.1 km upstream of the outfall, at the effluent outfall, and 0.1 km below the outfall) during base-flow conditions from two months (January and May) of a temperate-region effluent-dominated stream containing a complex mixture of pharmaceuticals and other contaminants of emerging concern. RNA-sequencing identified potential biological impacts and biomarkers of WWTP effluent exposure that extend past traditional markers of endocrine disruption. Transcriptomics revealed changes to a wide range of biological functions and pathways including cardiac, neurological, visual, metabolic, and signaling pathways. These transcriptomic changes varied by developmental stage and displayed sensitivity to variable chemical composition and concentration of effluent, thus indicating a need for stage-specific biomarkers. Some transcripts are known to be associated with genes related to pharmaceuticals that were present in the collected samples. Although traditional biomarkers of endocrine disruption were not enriched in either month, a high estrogenicity signal was detected upstream in May and implicates the presence of unidentified chemical inputs not captured by the targeted chemical analysis. This work reveals associations between bioeffects of exposure, stage of development, and the composition of chemical mixtures in effluent-dominated surface water. The work underscores the importance of measuring effects beyond the endocrine system when assessing the impact of bioactive chemicals in WWTP effluent and identifies a need for non-targeted chemical analysis when bioeffects are not explained by the targeted analysis

Gradient microfluidics enables rapid bacterial growth inhibition testing

Bacterial growth inhibition tests have become a standard measure of the adverse effects of inhibitors for a wide range of applications, such as toxicity testing in the medical and environmental sciences. However, conventional well-plate formats for these tests are laborious and provide limited information (often being restricted to an end-point assay). In this study, we have developed a microfluidic system that enables fast quantification of the effect of an inhibitor on bacteria growth and survival, within a single experiment. This format offers a unique combination of advantages, including long-term continuous flow culture, generation of concentration gradients, and single cell morphology tracking. Using Escherichia coli and the inhibitor amoxicillin as one model system, we show excellent agreement between an on-chip single cell-based assay and conventional methods to obtain quantitative measures of antibiotic inhibition (for example, minimum inhibition concentration). Furthermore, we show that our methods can provide additional information, over and above that of the standard well-plate assay, including kinetic information on growth inhibition and measurements of bacterial morphological dynamics over a wide range of inhibitor concentrations. Finally, using a second model system, we show that this chip-based systems does not require the bacteria to be labeled and is well suited for the study of naturally occurring species. We illustrate this using Nitrosomonas europaea, an environmentally important bacteria, and show that the chip system can lead to a significant reduction in the period required for growth and inhibition measurements (<4 days, compared to weeks in a culture flask)

Observation of two new Ξb−\Xi_b^- baryon resonances

Two structures are observed close to the kinematic threshold in the $\Xi_b^0 \pi^-$ mass spectrum in a sample of proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb$^{-1}$ recorded by the LHCb experiment. In the quark model, two baryonic resonances with quark content $bds$ are expected in this mass region: the spin-parity $J^P = \frac{1}{2}^+$ and $J^P=\frac{3}{2}^+$ states, denoted $\Xi_b^{\prime -}$ and $\Xi_b^{*-}$. Interpreting the structures as these resonances, we measure the mass differences and the width of the heavier state to be $m(\Xi_b^{\prime -}) - m(\Xi_b^0) - m(\pi^{-}) = 3.653 \pm 0.018 \pm 0.006$ MeV$/c^2$, $m(\Xi_b^{*-}) - m(\Xi_b^0) - m(\pi^{-}) = 23.96 \pm 0.12 \pm 0.06$ MeV$/c^2$, $\Gamma(\Xi_b^{*-}) = 1.65 \pm 0.31 \pm 0.10$ MeV, where the first and second uncertainties are statistical and systematic, respectively. The width of the lighter state is consistent with zero, and we place an upper limit of $\Gamma(\Xi_b^{\prime -}) < 0.08$ MeV at 95% confidence level. Relative production rates of these states are also reported.Comment: 17 pages, 2 figure