Search results for "Acetaldehyde"
showing 10 items of 90 documents
The paradoxical cyanide-stimulated respiration of Zymomonas mobilis: cyanide sensitivity of alcohol dehydrogenase (ADH II)
2003
The respiratory inhibitor cyanide stimulates growth of the ethanologenic bacteriumZymomonas mobilis, perhaps by diverting reducing equivalents from respiration to ethanol synthesis, thereby minimizing accumulation of toxic acetaldehyde. This study sought to identify cyanide-sensitive components of respiration. In aerobically grown, permeabilizedZ. mobiliscells, addition of 200 μM cyanide caused gradual inhibition of ADH II, the iron-containing alcohol dehydrogenase isoenzyme, which, in aerobic cultures, might be oxidizing ethanol and supplying NADH to the respiratory chain. In membrane preparations, NADH oxidase was inhibited more rapidly, but to a lesser extent, than ADH II. The time-cours…
Cyanide inhibits respiration yet stimulates aerobic growth of Zymomonas mobilis
2000
Potassium cyanide at submillimolar concentrations (20-500 microM) inhibited the high respiration rates of aerobic cultures of Zymomonas mobilis but, remarkably, stimulated culture growth. In batch culture, after an extended lag phase, exponential growth persisted longer, resulting in higher biomass densities. In aerobic chemostat cultures, elevated biomass concentration was observed in the presence of cyanide. This growth stimulation effect is attributed to decreased production of the inhibitory metabolite acetaldehyde at lowered respiration rates, when more reducing equivalents are channelled to alcohol dehydrogenase. Growth in the presence of cyanide did not alter the membrane cytochrome …
Neutral volatile compounds in the raw milks from different species
1993
SummaryA comparative study was carried out on the flavour constituents of bovine, ovine, caprine and water buffalo fresh raw milks. The volatiles were isolated from milks by means of vacuum distillation and liquid–liquid extraction. Eighty neutral volatile compounds were identified using high resolution gas chromatography (HRGC) and HRGC-mass spectrometry. About 30 of these components have not been detected previously in milk. The volatiles in milk were similar for the four species, although several quantitative differences might explain the different odours. The volatiles consisted mainly of ethyl esters, especially those derived from butyric and hexanoic acids. Dimethylsulphone alone comp…
Effect of oxidoreduction potential on aroma biosynthesis by lactic acid bacteria in nonfat yogurt
2011
; The aim of this study was to investigate the effect of oxidoreduction potential (Eh) on the biosynthesis of aroma compounds by lactic acid bacteria in non-fat yogurt. The study was done with yogurts fermented by Lactobacillus bulgaricus and Streptococcus thermophilus. The Eh was modified by the application of different gaseous conditions (air, nitrogen, and nitrogen/hydrogen). Acetaldehyde, dimethyl sulfide, diacetyl, and pentane-2,3-dione, as the major endogenous odorant compounds of yogurt, were chosen as tracers for the biosynthesis of aroma compounds by lactic acid bacteria. Oxidative conditions favored the production of acetaldehyde, dimethyl sulfide, and diketones (diacetyl and pen…
Engineering a Saccharomyces cerevisiae Wine Yeast That Exhibits Reduced Ethanol Production during Fermentation under Controlled Microoxygenation Cond…
2006
ABSTRACTWe recently showed that expressing an H2O-NADH oxidase inSaccharomyces cerevisiaedrastically reduces the intracellular NADH concentration and substantially alters the distribution of metabolic fluxes in the cell. Although the engineered strain produces a reduced amount of ethanol, a high level of acetaldehyde accumulates early in the process (1 g/liter), impairing growth and fermentation performance. To overcome these undesirable effects, we carried out a comprehensive analysis of the impact of oxygen on the metabolic network of the same NADH oxidase-expressing strain. While reducing the oxygen transfer rate led to a gradual recovery of the growth and fermentation performance, its i…
Molar growth yields ofZymomonas mobilis on glucose after the transition from anaerobic to aerobic continuous growth
1999
An increase in the molar growth yield (Y X/S = 14.3-20.3 g/mol) on glucose (25 mM) was achieved after the transition of Zymomonas mobilis ATCC 29191 from anaerobic to aerobic steady state growth at dilution rates of D = 0.31-0.40 1/h and under oxygen-unlimited conditions. The transfer of anaerobically or aerobically grown steady state cells into a fresh medium resulted in the higher values of Y X/S . A positive correlation was established between biomass and acetaldehyde yield within the range of 5-9 mM acetaldehyde in the medium. An inhibitory effect of the exogenously added acetaldehyde (Kj = 16.7 ± 2.8 mM) on the ATPase activity was observed in vitro, using cell-free extracts of anaerobi…
Acetaldehyd als Indicator f�r die Regulation von Atmung und G�rung bei der aeroben Verg�rung von Glucose durch Saccharomyces cerevisiae
1971
Wahrend der aeroben Vergarung von Glucose wurde die Konzentration von Acetaldehyd im Garmedium uber den gesamten Garablauf bei mehreren Stammen von Saccharomyces cerevisiae verfolgt. Die Aldehydkonzentration weist bei Glucosekonzentrationen zwischen 5 und 20% zwei Maxima auf. Damit ist der Konzentrationsverlauf von Acetaldehyd aerob wesentlich anders als bei der anaeroben Garung, mit nur einem meist niedrigen Maximum. 10-3 M Azid hemmt die Bildung von Acetaldehyd ganz oder weitgehend. Das deutet auf die Funktion bzw. Synthese der Cytochrome, die in Gegenwart von Sauerstoff offensichtlich auch bei hohen Glucosekonzentrationen nicht vollstandig reprimiert werden. Der durch die Atmung bedingte…
Maximum exposure levels for xylene, formaldehyde and acetaldehyde in cars.
2004
Although millions of individuals are exposed to emissions from articles inside cars, relatively little has been published about possible adverse health effects and about exposure levels that can be considered safe or "acceptable". Xylene, formaldehyde and acetaldehyde represent typical examples of relevant volatile organic substances (VOC) released from articles inside cars. Recently, a concept for derivation of maximum exposure levels for volatile organic substances in cars has been published. In the present study we applied this concept to derive maximum exposure levels for xylene, formaldehyde and acetaldehyde and compared the resulting concentrations to exposure levels usually found ins…
Mitochondrial oxidative stress and CD95 ligand: A dual mechanism for hepatocyte apoptosis in chronic alcoholism
2002
Apoptosis plays an important role in the progression of alcohol-induced liver disease to cirrhosis. Oxidative stress is an early event in the development of apoptosis. The major aim of this study was to study the conditions in which oxidative stress occurs in chronic alcoholism and its relationship with apoptosis of hepatocytes. We have found that oxidative stress is associated with chronic ethanol consumption in humans and in rats, in the former independently of the existence of alcohol-induced liver disease. Ethanol or acetaldehyde induces apoptosis in hepatocytes isolated from alcoholic rats, but not in those from control rats. Inhibition of aldehyde dehydrogenase, but not of cytochrome …
Über die cyclopolymerisation einiger bis-(N-vinyl)-verbindungen
1966
Durch Umsetzung von Vinylisocyanat mitAthylenglykol, Butandiol-1,4, Hexandiol-1,6, Octandiol-1,8, Brenzcatechin, Resorcin, Hydrochinon, cis- und trans-Chinit sowie Piperazin wurden die entsprechenden Bis-(N-vinyl)-Verbindungen hergestellt. Diese Monomeren werden unter gleichen Bedingungen radikalisch polymerisiert. Der Gehalt an seitenstandigen N-Vinylgruppen ergibt sich aus der bei saurer Hydrolyse gebildeten Menge Acetaldehyd. Der auf 0% Umsatz berechnete Doppelbindungsgehalt und damit der Cyclisierungsgrad hangt von der Struktur der Monomeren ab. Die Ergebnisse stimmen uberein mit der Ringbildungstendenz bei niedermolekularen Verbindungen (z. B. Ansaverbindungen) und werden an Hand von M…