Impact of coffee preparation on total phenolic content in brewed coffee extracts and their contribution to the body’s antioxidant status

Food Science and Biotechnology - Although coffee has been reported as a major contributor to antioxidants in the diet, there are limited studies assessing how brewing methods and types of coffee...     

Mammalian Cytochrome P450-Dependent Metabolism of Polychlorinated Dibenzo-p-dioxins and Coplanar Polychlorinated Biphenyls

Polychlorinated dibenzo-p-dioxins (PCDDs) and coplanar polychlorinated biphenyls (PCBs) contribute to dioxin toxicity in humans and wildlife after bioaccumulation through the food chain from the environment. The authors examined human and rat cytochrome P450 (CYP)-dependent metabolism of PCDDs and PCBs. A number of human CYP isoforms belonging to the CYP1 and CYP2 families showed remarkable activities toward low-chlorinated PCDDs. In particular, human CYP1A1, CYP1A2, and CYP1B1 showed high activities toward monoCDDs, diCDDs, and triCDDs but no detectable activity toward 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-tetraCDD). Large amino acids located at putative substrate-recognition sites and the F-G loop in rat CYP1A1 contributed to the successful metabolism of 2,3,7,8-tetraCDD. Rat, but not human, CYP1A1 metabolized 3,3'',4,4'',5-pentachlorobiphenyl (CB126) to two hydroxylated metabolites. These metabolites are probably less toxic than is CB126, due to their higher solubility. Homology models of human and rat CYP1A1s and CB126 docking studies indicated that two amino acid differences in the CB126-binding cavity were important for CB126 metabolism. In this review, the importance of CYPs in the metabolism of dioxins and PCBs in mammals and the species-based differences between humans and rats are described. In addition, the authors reveal the molecular mechanism behind the binding modes of dioxins and PCBs in the heme pocket of CYPs.     

Effects of polyglycerol esters of fatty acids and ethylene‐vinyl acetate co‐polymer on crystallization behavior of biodiesel

Biodiesel fuels (BDF) have many problems in the cold due to their crystallization properties. In particular, precipitation of large crystals of high‐melting fractions in BDF at low temperatures remarkably changes cold flow property of BDF and, thereby, it increases the values of cold filter plugging point. In this study, we evaluated polyglycerol esters of fatty acids (PGE) and ethylene‐vinyl acetate co‐polymer (EVA) as chemical additives to improve the cold flow property of palm oil‐based FAME (PFME). The results of solid fat content measurement indicate that the simultaneous addition of PGE and EVA showed synergistic effects on suppression of crystallization of PFME, however such effect was not observed when EVA was used alone. DSC thermograms indicated that the PGE additives not only decreased the crystallization temperature but also kinetically suppressed the crystal growth. Polarized light microscopy showed that the simultaneous addition of PGE and EVA led to the formation of considerably small and fine‐dispersed crystals of PFME. These results indicate that combined effects of PGE and EVA caused the formation of fine‐dispersed PFME crystals, which could improve the viscous properties of palm oil‐based BDF at relatively cold temperatures.     

Kinetic studies on lipase-catalyzed acetylation of 2-alkanol with vinyl acetate in organic solvent

Lipase-catalyzed acetylation of 2-alkanol with vinyl acetate has been studied kinetically using Burkholderia cepacia lipase (BCL), enantiomerically pure (R)- and (S)-2-alkanols and different organic solvents. The rate equation was derived by the steady state method for the simplified mechanism. The second order rate constants (k(R) and k(S)) for (R)- and (S)-2-alkanols were evaluated from the slopes of the double reciprocal plots, v(-1) vs. [2-alkanol](-1), where v is the initial rate of the reaction. The log k(R) value increased with the solvent hydrophobicity log P, where P is a partition coefficient of a given solvent between octanol and water. The log k(S) value also increased with log P except the bulky solvents such as 1,4-dioxane and cyclohexane, in which the rates were faster than those expected from the log k(S) vs. log P plot. The slope of log k(S) vs. log P plot was larger than that for (R)-2-alkanol. Thus, log E (E=k(R)/k(S): enantioselectivity) decreased with log P except the bulky solvents. The rate constants and the enantioselectivity were different depending on the structure (carbon number CN) of 2-alkanol. The log E vs. CN plot was minimized at CN=8 and 10 and the log k(S) vs. CN plot maximized at CN=8 and 10. In contrast the log k(R) vs. CN plot showed a different feature from the log E vs. CN plot. These facts suggest that dependence of E on CN is more strongly affected by the reactivity of (S)-2-alkanol than that of (R) isomer in this acetylation.     

Processing of ethanol fermentation broths by Candida krusei to separate bioethanol by pervaporation using silicone rubber‐coated silicalite membranes

BACKGROUND: Pervaporation employing ethanol‐permselective silicalite membranes as an alternative to distillation is a promising approach for refining low‐concentration bioethanol solutions. However, to make the separation process practicable, it is extremely important to avoid the problems caused by the adsorption of succinate on the membrane during the separation process. In this work, the pervaporation of an ethanol fermentation broth without succinate was investigated, as well as the influence of several fermentation broth nutrient components. RESULTS: Candida krusei IA‐1 produces an extremely low level of succinate. The decrease in permeate ethanol concentration through a silicone rubber‐coated silicalite membrane during the separation of low‐succinate C. krusei IA‐1 fermentation broth was significantly improved when compared with that obtained using Saccharomyces cerevisiae broth. By treating the fermentation broth with activated carbon, bioethanol was concentrated as efficiently as with binary mixtures of ethanol/water. The total flux was improved upto 56% of that obtained from the separation of binary mixtures, compared with 43% before the addition of activated carbon. Nutrients such as peptone, yeast extract and corn steep liquor had a negative effect on pervaporation, but this response was distinct from that caused by succinate. CONCLUSION: For consistent separation of bioethanol from C. krusei IA‐1 fermentation broth by pervaporation, it is useful to treat the low nutrient broth with activated carbon. To further improve pervaporation performance, it will be necessary to suppress the accumulation of glycerol. Copyright © 2009 Society of Chemical Industry     

Reduction and unusual recovery in the reversible hydrogen storage capacity of V1−xTix during hydrogen cycling

The effect of the vanadium content on the cyclic stability of V–Ti binary alloys was investigated. V_1−xTi_x, x = 0.2 and 0.5 samples were hydrogenated and dehydrogenated at 410 K and 553 K respectively, for more than 100 times. During hydrogen cycling, reduction in the reversible hydrogen storage capacity was clearly observed from both samples. No prominent V-effect was found. In fact, the reduction rates of two samples were similar; both samples showed a ∼25% reduction in the reversible hydrogen storage capacity after 100 cycles. In addition, the shape of the pressure–composition-isotherm (PCT) curves was significantly altered over the testing cycle period; the absorption and desorption plateaus got markedly inclined and the hysteresis became evidently smaller. We found that even after the hydrogen storage capacity of V_1−xTi_x was significantly reduced, at low enough temperature V_1−xTi_x was able to absorb hydrogen as much as it did at the first cycle. Furthermore, the reversible hydrogen storage capacity of V_0.8Ti_0.2 at 410 K was recovered to a certain degree after hydrogenating the sample at low temperatures.     

Resonant tunneling in quantum heterostructures: electron transport,dynamics, and device applications

The current understanding of the resonant tunneling process of electrons in double-barrier (DB) diodes and in coupled quantum well structures is described. The authors examine the validity of the simple Fabry-Perot model in describing the electron transport in actual DB diodes. They then describe a picosecond laser study to clarify the dynamics of resonant tunneling, including the intrinsic time delay associated with the multiple reflection of electron waves. Lastly, they discuss both the current state and prospects of device applications for high-speed electronics and optoelectronics     

Presenilin 1 mutations linked to familial Alzheimer's disease increase the intracellular levels of amyloid beta-protein 1-42 and its N-terminally truncated variant(s) which are generated at distinct sites

Mutations in the presenilin genes PS1 and PS2 cause the most common form of early-onset familial Alzheimer's disease. The influence of PS1 mutations on the generation of endogenous intracellular amyloid beta-protein (A beta) species was assessed using a highly sensitive immunoblotting technique with inducible mouse neuroblastoma (Neuro 2a) cell lines expressing the human wild-type (wt) or mutated PS1 (M146L or delta exon 10). The induction of mutated PS1 increased the intracellular levels of two distinct A beta species ending at residue 42 that were likely to be A beta1-42 and its N-terminally truncated variant(s) A beta x-42. The induction of mutated PS1 resulted in a higher level of intracellular A beta1-42 than of intracellular A beta x-42, whereas extracellular levels of A beta1-42 and A beta x-42 were increased proportionally. In addition, the intracellular generation of these A beta42 species in wt and mutated PS1-induced cells was completely blocked by brefeldin A, whereas it exhibited differential sensitivities to monensin: the increased accumulation of intracellular A beta x-42 versus inhibition of intracellular A beta1-42 generation. These data strongly suggest that A beta x-42 is generated in a proximal Golgi, whereas A beta1-42 is generated in a distal Golgi and/or a post-Golgi compartment. Thus, it appears that PS1 mutations enhance the degree of 42-specific gamma-secretase cleavage that occurs in the normal beta-amyloid precursor protein processing pathway (a) in the endoplasmic reticulum or the early Golgi apparatus prior to beta-secretase cleavage or (b) in the distinct sites where A beta x-42 and A beta1-42 are generated.     

Gate-controlled modulation of electronic states and conductance in coupled quantum wells having an in-plane periodic potential

We investigated theoretically a unique way to control the dispersion relation of electrons by using a novel double quantum well (DQW) structure, in which an in-plane periodic potential is introduced to one of the channels. It is demonstrated that the effective mass in this system can be abruptly changed by the gate-controlled resonant coupling, resulting in a switching of the channel current. We discuss also a few feasible schemes to achieve the effective mass modulation and their possible applications to the velocity modulation transistor.     

Brainstem auditory evoked potentials during brainstem ischemia and reperfusion in gerbils

To evaluate the reversibility of neural function in the brainstem following ischemia, we investigated the effect of transient brainstem ischemia on the brainstem auditory evoked potential in gerbils. Brainstem ischemia was produced by bilateral extracranial occlusion of vertebral arteries. Local cerebral blood flow was measured by quantitative autoradiography after 5 min of ischemia and was reduced to less than 3 ml/100 g per min in the pons and lower midbrain, indicating severe and reproducible brainstem ischemia. During brainstem ischemia, brainstem auditory evoked potential waveforms disappeared completely. After a brief ischemic insult (5 min), all four brainstem auditory evoked potential components recovered to normal. After longer ischemic insults (10-30 min), brainstem auditory evoked potential components never recovered to normal. Microtubule-associated protein 2 immunoreactivity revealed differential vulnerability of the acoustic relay nuclei in the brainstem. Neurons in the lateral lemniscus were most vulnerable, followed in order by neurons in the trapezoid body, the superior olive and the cochlear nucleus. We also demonstrated a close relationship between the reversibility of ischemia-induced changes on brainstem auditory evoked potential and ischemic lesions of these relay nuclei. These data may be useful for evaluating the therapeutic window of thrombolytic therapy during acute vertebrobasilar occlusion.