Impact of Roasting Conditions on the Formation of Aroma Compounds in Coffee Beans

ABSTRACT: Hot air roasting of coffee beans results in a large number of aroma compounds. For a given coffee, the aroma profile is determined by the specific conditions for chemical reactions as controlled by the process parameters. Therefore, the influence of roasting temperatures on the formation of key aroma compounds was investigated. Coffee was roasted in 6 different processes to equal degrees of roast and the developing aroma compound profiles were characterized by gas chromatography, mass spectrometry, and olfactometry. A majority of aroma compounds showed the highest increase in concentration at medium stage of dehydration with bean water content from 7 to 2% (wb). Different time-temperature histories led to distinct aroma compound profiles. To reach a specific flavor profile, precise control of roasting time and temperature is required.     

Determination of hemin-binding characteristics of proteins by a combinatorial peptide library approach

Studies of the binding of heme/hemin to proteins or peptides have recently intensified as it became evident that heme serves not only as a prosthetic group, but also as a regulator and effector molecule interacting with transmembrane and cytoplasmic proteins. The iron‐ion‐containing heme group can associate with these proteins in different ways, with the amino acids Cys, His, and Tyr allowing individual modes of binding. Strong coordinate‐covalent binding, such as in cytochrome c, is known, and reversible attachment is also discussed. Ligands for both types of binding have been reported independently, though sometimes with different affinities for similar sequences. We applied a combinatorial approach using the library (X)₄(C/H/Y)(X)₄ to characterize peptide ligands with considerable hemin binding capacities. Some of the library‐selected peptides were comparable in terms of hemin association independently of whether or not a cysteine residue was present in the sequence. Indeed, a preference for His‐based (≈39 %) and Tyr‐based (≈40 %) sequences over Cys‐based ones (≈21 %) was detected. The binding affinities for the library‐selected peptides, as determined by UV/Vis spectroscopy, were in the nanomolar range. Moreover, selected representatives efficiently competed for hemin binding with the human BK channel hSlo1, which is known to be regulated by heme through binding to its heme‐binding domain.     

Spillover effects when IKEA enters: Do incumbent retailers win or lose?

We investigate the effects of IKEA entry in three Swedish municipalities, finding that revenues for incumbent retailers located 1 km from the new IKEA store experienced a 7% increase due to positive spillover. The effect was insignificant for retailers located in city centres or more than 1 km from IKEA. Moreover, the positive agglomeration effects only dominate the negative competition effects for stores that sell complementary products, while same-market retailers located between 2 and 5 km from the new IKEA store experienced revenue loss due to IKEA entry. In contrast to retail revenues, the effects on employment were statistically insignificant.     

Individual Driving Behaviour in Wildfire Smoke

Fire Technology - This work presents the results of a virtual reality (VR) experiment aiming at investigating how individual driving behaviour is affected by the presence of wildfire smoke. The...     

A quantitative assessment of the hydrogen storage capacity of the UK continental shelf

Increased penetration of renewable energy sources and decarbonisation of the UK's gas supply will require large-scale energy storage. Using hydrogen as an energy storage vector, we estimate that 150 TWh of seasonal storage is required to replace seasonal variations in natural gas production. Large-scale storage is best suited to porous rock reservoirs. We present a method to quantify the hydrogen storage capacity of gas fields and saline aquifers using data previously used to assess CO₂ storage potential. We calculate a P50 value of 6900 TWh of working gas capacity in gas fields and 2200 TWh in saline aquifers on the UK continental shelf, assuming a cushion gas requirement of 50%. Sensitivity analysis reveals low temperature storage sites with sealing rocks that can withstand high pressures are ideal sites. Gas fields in the Southern North Sea could utilise existing infrastructure and large offshore wind developments to develop large-scale offshore hydrogen production.     

The Müller (glial) cell in normal and diseased retina: a case for single-cell electrophysiology

In the retina of most vertebrates there exists only one type of macroglia, the Müller cell. Müller cells express voltage-gated ion channels, neurotransmitter receptors and various uptake carrier systems. These properties enable the Müller cells to control the activity of retinal neurons by regulating the extracellular concentration of neuroactive substances such as K+, GABA and glutamate. We show here how electrophysiological recordings from enzymatically dissociated mammalian Müller cells can be used to study these mechanisms. Müller cells from various species have Na(+)-dependent GABA uptake carriers, but only cells from primates have additional GABA receptors that activate Cl- channels. Application of glutamate analogues causes enhanced membrane currents recorded from Müller cells in situ but not from isolated cells. We show that mammalian Müller cells have no ionotropic glutamate receptors but respond to increased K+ release from glutamate-stimulated retinal neurons. This response is involved in extracellular K+ clearance and is mediated by voltage-gated (inwardly rectifying) K+ channels which are abundantly expressed by healthy Müller cells. In various cases of human retinal pathology, currents through these channels are strongly reduced or even extinguished. Another type of voltage-gated ion channels, observed in Müller cells from many mammalian species, are Na+ channels. In Müller cells from diseased human retinae, voltage-dependent Na+ currents were significantly increased in comparison to cells from control donors. Thus, the expression of glial ion channels seems to be controlled by neuronal signals. This interaction may be involved in the pathogenesis of retinal gliosis which inevitably accompanies any degeneration of retinal neurons. In particular, Müller cell proliferation may be triggered by mechanisms requiring the activation of Ca(2+)-dependent K+ channels. Ca(2+)-dependent K+ currents are easily elicitable in Müller cells from degenerating retinae and can be blocked by 1 mM TEA (tetraethylammonium). In purified Müller cell cultures, the application of 1 mM TEA greatly reduces the proliferative activity of the cells. These data clearly show that Müller cells are altered in cases of neuronal degeneration and may be crucially involved in pathogenetic mechanisms of the retina.