Elevated Ethanol Concentrations Research Articles

The joint action of yeast eisosomes and membraneless organelles in response to ethanol stress

Elevated ethanol concentrations in yeast affect the plasma membrane. The plasma membrane in yeast has many lipid-protein complexes, such as Pma1 (MCP), Can1 (MCC), and the eisosome complex. We investigated the response of eisosomes, MCPs, and membraneless structures to ethanol stress. We found a correlation between ethanol stress and proton flux with quick acidification of the medium. Moreover, ethanol stress influences the symporter expression in stressed cells. We also suggest that acute stress from ethanol leads to increases in eisosome size and SG number: we hypothesized that eisosomes may protect APC symporters and accumulate an mRNA decay protein in ethanol-stressed cells. Our findings suggest that the joint action of these factors may provide a protective effect on cells under ethanol stress.

A mutant GH3 family β-glucosidase from Oenococcus oeni exhibits superior adaptation to wine stresses and potential for improving wine aroma and phenolic profiles

In this study, we conducted a comprehensive investigation into a GH3 family β-glucosidase (BGL) from the wild-type strain of Oenococcus oeni and its mutated counterpart from the acid-tolerant mutant strain. Our analysis revealed the mutant BGL's remarkable capacity to adapt to wine-related stress conditions, including heightened tolerance to low pH, elevated ethanol concentrations, and metal ions. Additionally, the mutant BGL exhibited superior hydrolytic activity towards various substrates. Through de novo modeling, we identified specific amino acid mutations responsible for its resilience to low pH and high ethanol environments. In simulated wine conditions, the mutant BGL outperformed both wild-type and commercial BGLs, efficiently releasing terpene and phenolic aglycones from glycosides in wine grapes. These findings not only expand our understanding of O. oeni BGLs but also highlight their potential in enhancing wine production. The mutant BGL's enhanced adaptation to wine stress conditions opens promising avenue for improving wine quality and flavor.

Killing Two Birds With One Stone - Strain Engineering Facilitates the Development of a Unique Rhamnolipid Production Process.

High-titer biosurfactant production in aerated fermenters using hydrophilic substrates is often hampered by excessive foaming. Ethanol has been shown to efficiently destabilize foam of rhamnolipids, a popular group of biosurfactants. To exploit this feature, we used ethanol as carbon source and defoamer, without introducing novel challenges for rhamnolipid purification. In detail, we engineered the non-pathogenic Pseudomonas putida KT2440 for heterologous rhamnolipid production from ethanol. To obtain a strain with high growth rate on ethanol as sole carbon source at elevated ethanol concentrations, adaptive laboratory evolution (ALE) was performed. Genome re-sequencing allowed to allocate the phenotypic changes to emerged mutations. Several genes were affected and differentially expressed including alcohol and aldehyde dehydrogenases, potentially contributing to the increased growth rate on ethanol of 0.51 h–1 after ALE. Further, mutations in genes were found, which possibly led to increased ethanol tolerance. The engineered rhamnolipid producer was used in a fed-batch fermentation with automated ethanol addition over 23 h, which resulted in a 3-(3-hydroxyalkanoyloxy)alkanoates and mono-rhamnolipids concentration of about 5 g L–1. The ethanol concomitantly served as carbon source and defoamer with the advantage of increased rhamnolipid and biomass production. In summary, we present a unique combination of strain and process engineering that facilitated the development of a stable fed-batch fermentation for rhamnolipid production, circumventing mechanical or chemical foam disruption.

Tuning Enzyme Activity for Nonaqueous Solvents: Engineering an Enantioselective "Michaelase" for Catalysis in High Concentrations of Ethanol.

Enzymes have evolved to function under aqueous conditions and may not exhibit features essential for biocatalytic application, such as the ability to function in high concentrations of an organic solvent. Consequently, protein engineering is often required to tune an enzyme for catalysis in non‐aqueous solvents. In this study, we have used a collection of nearly all single mutants of 4‐oxalocrotonate tautomerase, which promiscuously catalyzes synthetically useful Michael‐type additions of acetaldehyde to various nitroolefins, to investigate the effect of each mutation on the ability of this enzyme to retain its “Michaelase” activity in elevated concentrations of ethanol. Examination of this mutability landscape allowed the identification of two hotspot positions, Ser30 and Ala33, at which mutations are beneficial for catalysis in high ethanol concentrations. The “hotspot” position Ala33 was then randomized in a highly enantioselective, but ethanol‐sensitive 4‐OT variant (L8F/M45Y/F50A) to generate an improved enzyme variant (L8F/A33I/M45Y/F50A) that showed great ethanol stability and efficiently catalyzes the enantioselective addition of acetaldehyde to nitrostyrene in 40 % ethanol (permitting high substrate loading) to give the desired γ‐nitroaldehyde product in excellent isolated yield (89 %) and enantiopurity (ee=98 %). The presented work demonstrates the power of mutability‐landscape‐guided enzyme engineering for efficient biocatalysis in non‐aqueous solvents.

Does Inter-Organellar Proteostasis Impact Yeast Quality and Performance During Beer Fermentation?

During beer production, yeast generate ethanol that is exported to the extracellular environment where it accumulates. Depending on the initial carbohydrate concentration in the wort, the amount of yeast biomass inoculated, the fermentation temperature, and the yeast attenuation capacity, a high concentration of ethanol can be achieved in beer. The increase in ethanol concentration as a consequence of the fermentation of high gravity (HG) or very high gravity (VHG) worts promotes deleterious pleiotropic effects on the yeast cells. Moderate concentrations of ethanol (5% v/v) change the enzymatic kinetics of proteins and affect biological processes, such as the cell cycle and metabolism, impacting the reuse of yeast for subsequent fermentation. However, high concentrations of ethanol (> 5% v/v) dramatically alter protein structure, leading to unfolded proteins as well as amorphous protein aggregates. It is noteworthy that the effects of elevated ethanol concentrations generated during beer fermentation resemble those of heat shock stress, with similar responses observed in both situations, such as the activation of proteostasis and protein quality control mechanisms in different cell compartments, including endoplasmic reticulum (ER), mitochondria, and cytosol. Despite the extensive published molecular and biochemical data regarding the roles of proteostasis in different organelles of yeast cells, little is known about how this mechanism impacts beer fermentation and how different proteostasis mechanisms found in ER, mitochondria, and cytosol communicate with each other during ethanol/fermentative stress. Supporting this integrative view, transcriptome data analysis was applied using publicly available information for a lager yeast strain grown under beer production conditions. The transcriptome data indicated upregulation of genes that encode chaperones, co-chaperones, unfolded protein response elements in ER and mitochondria, ubiquitin ligases, proteasome components, N-glycosylation quality control pathway proteins, and components of processing bodies (p-bodies) and stress granules (SGs) during lager beer fermentation. Thus, the main purpose of this hypothesis and theory manuscript is to provide a concise picture of how inter-organellar proteostasis mechanisms are connected with one another and with biological processes that may modulate the viability and/or vitality of yeast populations during HG/VHG beer fermentation and serial repitching.

Variability of ethanol concentration in rainwater driven by origin versus season in coastal and inland North Carolina, USA

Rainwater ethanol concentrations were measured for one year (June 2013–May 2014) in central (Elon, NC) and coastal (Wilmington, NC) North Carolina, allowing for a comparison of the effects of coastal and marine rain on ethanol concentration and deposition both at the coast and 250 km inland. Rain samples were collected on an event basis and analyzed using enzyme oxidation and headspace solid-phase microextraction (HS-SPME). The volume-weighted average ethanol concentration at Elon (609 ± 116 nM) was higher than at Wilmington (208 ± 21 nM). Rainfall influenced by air masses originating over the Atlantic Ocean has previously been observed to be lower in ethanol concentration than terrestrial rain at the Wilmington location, and this was true during this study as well. Lower-ethanol marine and coastal air masses did not affect the concentration of ethanol in Elon rain, 250 km from the coast. This is likely due to the rapid supply of locally emitted ethanol to air masses moving over the land. No difference in rainwater ethanol concentrations was observed for Elon rain based on air mass back trajectories, most likely because all the rain was impacted by both anthropogenic and biogenic terrestrial sources typical of most inland areas. Seasonal variation in ethanol concentrations was significant in the inland location with elevated ethanol concentrations observed in fall; no seasonal variation was observed in coastal location rain. This study presents for the first time the different drivers for ethanol concentrations in rainwater from a coastal and a proximal inland location.

Impact of Extracellular Osmolality on Saccharomyces Yeast Populations during Brewing Fermentations

Osmotic stress represents one of the major environmental challenges experienced by yeast during industrial fermentations. This stress is particularly associated with high-gravity processes, which utilize concentrated substrates to yield products with elevated concentrations of ethanol. The aims of this work were to quantitatively measure factors affecting extracellular osmotic pressure (osmolality) during brewing fermentations and to determine their effects on yeast at the physiological and molecular level. Osmolality was observed to increase during fermentation owing predominantly to ethanol production, indicating a strong relationship between these environmental parameters. High osmolality was shown to have a negative impact on yeast physiology, viability, and vitality, and although genome integrity was unaffected, cell membrane fluidity became altered. These data not only demonstrate the occurrence of an increase in osmotic pressure during fermentation but also provide an explanation for the decrease in yeast quality typically observed under high-gravity conditions. The results presented here are directly relevant to all brewery fermentations worldwide and have applications within associated industries in which microorganisms are used for ethanol production, including food products, alcoholic beverages, and biofuels.

Strategies for reducing alcohol concentration in wine

Extending the time before harvest—and therefore increasing grape maturity—enhances ripe fruit wine flavours and wine colour intensity, and also decreases unripe green and vegetal wine flavours. Greater maturity, however, increases sugar concentration, which in turn leads to wines with elevated ethanol concentration. High ethanol concentration can reduce the complexity of a wine by suppressing aroma intensity, while also increasing the perception of ‘hotness’ and ‘bitterness’. In addition, health and economic considerations combined with market demand have the wine industry actively seeking ways to facilitate the production of wines with lower alcohol concentration. This review summarises the latest research aimed at reducing wine alcohol concentration, including viticultural practices, pre-fermentation and winemaking practices, microbiological strategies, and post-fermentation approaches and processing technologies. The effect of these practices on wine flavour is also discussed.

Ethanol accumulation during severe drought may signal tree vulnerability to detection and attack by bark beetles

Tree mortality from temperature-driven drought is occurring in forests around the world, often in conjunction with bark beetle outbreaks when carbon allocation to tree defense declines. Physiological metrics for detecting stressed trees with enhanced vulnerability prior to bark beetle attacks remain elusive. Ethanol, water, monoterpene concentrations, and composition were examined in the phloem and sapwood of drought-stressed Aleppo pine (Pinus halepensis Mill.) freshly attacked by mature Mediterranean pine shoot beetles (Tomicus destruens (Wollaston, 1865)) and in neighboring unattacked trees. The attacked trees were more water-stressed and contained, on average, 2.1 and 2.4 times more ethanol in the phloem and sapwood, respectively, than the neighboring attack-free trees. This response is consistent with the known attraction of T. destruens to ethanol. Most monoterpene concentrations in the phloem, but not sapwood, were greater in tissues of attacked trees, whereas compositional differences were minor between the two tree groups for both tissues. Tissue water content explained much of the variation in phloem monoterpene concentrations, which increased as water in the phloem declined, suggesting that higher constitutive quantities existed in the more stressed trees prior to the attacks. Monoterpenes may have contributed to host tree selection by T. destruens, but their potential influence is considered less important than that of ethanol based on beetle responses to these compounds in previous trapping studies. This is the first report of elevated ethanol concentrations in tissues of trees experiencing natural drought stress and suggests that ethanol measurements in severely water-stressed trees may allow early detection of those most vulnerable to bark beetle attack.

Outcomes for older trauma patients in the emergency department screening positive for alcohol, cocaine, or marijuana use

Background: Substance use among older adults is an increasing concern, with the prevalence of substance use in older populations expected to double in the next decade. Drug and alcohol use is associated with trauma risk and outcomes, but little is known about the specific risk for older trauma patients. Objectives: To evaluate the association between drug and alcohol use and trauma outcomes among adults aged 55 years and older. Methods: This retrospective observational study included older adults from the Illinois Trauma Registry between 1999 and 2009. Exclusion criteria were age younger than 55 years or absent date of birth, ethanol level, or urine drug screen (UDS). Alcohol intoxication was defined as ethanol level greater than 80 mg/dL. UDS was used to screen cocaine and marijuana use. Analyses, for both the alcohol and the marijuana/cocaine groups, compared outcomes for patients with negative vs. positive screens. Results: 21 320 patients were included in the alcohol analysis and 17 077 in the drug analysis. Compared to non-intoxicated patients, alcohol-intoxicated patients had significantly (p < 0.001) lower in-hospital mortality, decreased ICU admission, decreased intubation rate, and shorter hospital length of stay. Patients screening positive for cocaine or marijuana had significantly longer lengths of stay with increased ICU admission compared with those who screened negative. Conclusion: Among older trauma patients, this study shows significant associations with multiple trauma outcomes, including one between elevated ethanol concentrations and improved outcomes. Future research into the causes of these findings could inform the care of older trauma patients and aid in prevention of injuries.

Cloning, expression and characterization of an ethanol tolerant GH3 β-glucosidase fromMyceliophthora thermophila

The β-glucosidase gene bgl3a from Myceliophthora thermophila, member of the fungal glycosyl hydrolase (GH) family 3, was cloned and expressed in Pichia pastoris. The mature β-glucosidase gene, which results after the excision of one intron and the secreting signal peptide, was placed under the control of the strong alcohol oxidase promoter (AOX1) in the plasmid pPICZαC. The recombinant enzyme (90 kDa) was purified and characterized in order to evaluate its biotechnological potential. Recombinant P. pastoris efficiently secreted β-glucosidase into the medium and produced high level of enzymatic activity (41 U/ml) after 192 h of growth, under methanol induction. MtBgl3a was able to hydrolyze low molecular weight substrates and polysaccharides containing β-glucosidic residues. The Km was found to be 0.39 mM on p-β-NPG and 2.64 mM on cellobiose. Optimal pH and temperature for the p-β-NPG hydrolysis were 5.0 and 70 °C. The β-glucosidase exhibits a half life of 143 min at 60 °C. Kinetic parameters of inhibition were determined for D-glucose, D-xylose and D-gluconic acid, indicating tolerance of the enzyme for these sugars and oxidized products. The recombinant enzyme was stimulated by short chain alcohols and has been shown to efficiently synthesize methyl-D-glucoside in the presence of methanol due to its transglycosylation activity. The stability of MtBgl3a in ethanol was prominent, and it retained most of its original activity after we exposed it to 50% ethanol for 6 h. The high catalytic performance, good thermal stability and tolerance to elevated concentrations of ethanol, D-xylose and D-glucose qualify this enzyme for use in the hydrolysis of lignocellulosic biomass for biofuel production, as part of an efficient complete multi-enzyme cocktail.

Withdrawal symptoms after gabapentin discontinuation

A case of apparent gabapentin withdrawal symptoms after discontinuation of gabapentin therapy is reported. A 53-year-old woman had coffee ground emesis, a two-day history of black tarry stools, and abdominal pain. The patient did have an elevated ethanol concentration (323 mg/dL), with the last reported ingestion of ethanol about 12 hours before admission. Her medical history included liver cirrhosis secondary to ethanol abuse, ascites, portal hypertension, esophageal varices (with previous band ligation three weeks prior), anemia, gastroesophageal reflux disease, neuropathic pain, and depression. Her home medications included spironolactone, nadolol, lactulose, ursodiol, ferrous sulfate, omeprazole, gabapentin, citalopram, and trazodone. She was admitted to the intensive care unit, and upper gastrointestinal endoscopy was performed, with 12 band ligations applied. After the procedure, she ingested nothing orally, including home medications, for the first two days. On day 3 of hospitalization, she developed restlessness, disorientation, confusion, agitation, and anxiety. She was presumed to be suffering from ethanol withdrawal and was treated with benzodiazepines but had no improvement in symptoms. During days 4 and 5, the patient became increasingly confused, agitated, and anxious, with complaints of headache, light sensitivity, and increasing nervousness. On day 5, gabapentin was reinitiated, and the patient's confusion and agitation improved that evening. The next morning, the patient was calm, alert, and cooperative. Her symptoms resolved, and she was discharged on hospital day 7. A patient developed apparent withdrawal symptoms beginning two days after gabapentin therapy was discontinued. The symptoms were unresponsive to treatment with benzodiazepines but completely resolved with the reinitiation of gabapentin therapy.

Beer with Reduced Ethanol Content Produced Using Saccharomyces cerevisiae Yeasts Deficient in Various Tricarboxylic Acid Cycle Enzymes

J. Inst. Brew. 114(2), 97–101, 2008 A collection of Saccharomyces cerevisiae strains deficient in the tricarboxylic acid cycle enzymes activities has been examined for the production of beer with reduced ethanol content. Strains deficient in fumarase and α-ketoglutarate dehydrogenase encoded by the genes FUM1 (0.48%), KGD1 (0.42%) and KGD2 (0.48%) made non-alcoholic beers with an alcohol content lower than 0.5% (v/v). The rest of the yeast mutants also gave rise to low-alcoholic beers but with a slightly elevated ethanol concentration (mostly in the range of 0.57–0.84% and 1.64% for the lip5 mutant). Low ethanol content was compensated by the considerable increase of organic acids (citrate succinate, fumarate, and malate). In addition, some of the mutants released high levels of lactic acid (144 (fum1), 622 (kgd1) and 495 (kgd2) mg/L). Lactic acid protects beers against contamination and masks an unacceptable worty off-flavour.

Effects of glycerol on the thermal dependence of the stability of human erythrocytes

Incubation of human blood in saline solution of 0-36% (v/v) ethanol for 30 min produces lysis or stabilization of erythrocytes depending on the ethanol concentration. Under less elevated concentrations of ethanol, erythrocytes are present in expanded shapes (R state) that present lower stability and suffer lysis with increase in the ethanol concentration. Under more elevated concentrations of ethanol, erythrocytes are present in contracted shapes (T state) that have higher stability and suffer lysis at even more elevated ethanol concentrations. This work evaluated the effects of glycerol (0 to 2.0 M) and temperature (7 to 47 degrees C) on the stability of the R erythrocytes, characterized by the ethanol concentration at the mid-transition point (D (50R )) of the hemolysis curve (D (50R )). D (50R ) declined sigmoidally with increase in the glycerol concentration or temperature, due to transition of the R to the T state erythrocytes. In 1.5 M glycerol, the erythrocytes stability decreased below 32 but increased above 37 degrees C. The combination of temperature, glycerol and ethanol actions generates a critical value of osmotic pressure below which the R state predominates and above which the T state predominates. At 7 degrees C 1.5 M glycerol decreased the erythrocytes stability against ethanol but increased the erythrocytes stability against hypotonic shock. Those conditions favor the R state, which has a lower stability against ethanol; however, in the absence of ethanol, glycerol determines less water entrance in the erythrocytes, making more difficult its lysis by hypotonicity.

DEGRADATION KINETICS OF ANTHOCYANIN IN ETHANOLIC SOLUTIONS

The objective of this study was to investigate the degradation kinetics of anthocyanin in ethanolic model solutions simulating wine and liqueur in aging or long-term storage. Malvidin-3-glucoside, as the predominant anthocyanin in many cultivars of grape, was chosen to represent anthocyanins. The results from high performance liquid chromatography analysis show that the disappearance of malvidin-3-glucoside follows apparent first-order kinetics, and accelerates with the increase in ethanol concentration. The Ea values were found to be 22.80, 24.45, 24.35 and 22.75 kcal/mole at 0, 10, 30 and 50% ethanol concentrations, respectively. We propose that the decreased stability of anthocyanin at an elevated ethanol concentration is a result of a decreased extent of self-association in the solution.

Skin condition associated with intensive use of alcoholic gels for hand disinfection: a combination of biophysical and sensorial data

Although hand hygiene is an important and inexpensive measure to prevent nosocomial infections in clinical settings, the compliance of healthcare workers remains low. In Europe, alcoholic hand disinfection is first choice, but there exists a limited user acceptability due to estimated adverse effects on skin condition. This study was designed to investigate skin tolerance to alcohol-based disinfecting gels and changes in skin condition depending on humectant concentration, alcohol grades, as well as type of alcohol used. A comparison of 6 alcohol-based gels was made based on a randomized double-blind study under in use conditions for 1 day. Skin condition was evaluated by measuring transepidermal water loss (TEWL), stratum corneum hydration, apparent skin pH, redness and degree of scaliness. With respect to user acceptability, all gels were sensorially evaluated using a questionnaire. We saw that none of the alcohol-based gels, applied under in use conditions, altered TEWL or caused irritation. All gels hydrated the skin, proportionally to their glycerine content, and decreased skin pH. Elevated ethanol concentrations resulted in increased scaliness. Sensorial assessment revealed less appreciation for isopropanol. From this study, it was concluded that gels containing an elevated glycerine concentration and 70% (v/v) ethanol are preferred.

Very Low Ethanol Concentrations Affect the Viability and Growth Recovery in Post-Stationary-Phase Staphylococcus aureus Populations

Pharmaceuticals, culture media used for in vitro diagnostics and research, human body fluids, and environments can retain very low ethanol concentrations (VLEC) (< or =0.1%, vol/vol). In contrast to the well-established effects of elevated ethanol concentrations on bacteria, little is known about the consequences of exposure to VLEC. We supplemented growth media for Staphylococcus aureus strain DSM20231 with VLEC (VLEC(+) conditions) and determined ultramorphology, growth, and viability compared to those with unsupplemented media (VLEC(-) conditions) for prolonged culture times (up to 8 days). VLEC(+)-grown late-stationary-phase S. aureus displayed extensive alterations of cell integrity as shown by scanning electron microscopy. Surprisingly, while ethanol in the medium was completely metabolized during exponential phase, a profound delay of S. aureus post-stationary-phase recovery (>48 h) was observed. Concomitantly, under VLEC(+) conditions, the concentration of acetate in the culture medium remained elevated while that of ammonia was reduced, contributing to an acidic culture medium and suggesting decreased amino acid catabolism. Interestingly, amino acid depletion was not uniformly affected: under VLEC(+) conditions, glutamic acid, ornithine, and proline remained in the culture medium while the uptake of other amino acids was not affected. Supplementation with arginine, but not with other amino acids, was able to restore post-stationary-phase growth and viability. Taken together, these data demonstrate that VLEC have profound effects on the recovery of S. aureus even after ethanol depletion and delay the transition from primary to secondary metabolite catabolism. These data also suggest that the concentration of ethanol needed for bacteriostatic control of S. aureus is lower than that previously reported.

Estudo da reciclagem de células na produção biológica de etanol

Nas destilarias de álcool o conteúdo de etanol, na suspensão de levedura reciclada, gira em torno de 2% a 3%. A reciclagem de células é realizada tanto em fermentações em batelada, como nas contínuas. A fermentação alcoólica e a recuperação de células de leveduras foram avaliadas em laboratório. A levedura recuperada, por centrifugação, nos experimentos laboratoriais, foi tratada e novamente inoculada em novo meio fermentativo para avaliar o efeito tóxico do etanol e de outros metabólitos nas fermentações subseqüentes. A cepa Saccharomyces cerevisiae IZ-1904 utilizada foi inoculada em meio de melaço diluído contendo 180g L-1 e 310g L-1 de açúcares redutores totais (ART), com três repetições. O tratamento da levedura recuperada constou de dupla centrifugação e ressuspensão em água e vinho. Foram realizadas oito fermentações, a primeira com fermento multiplicado e as demais com a reciclagem de células das fermentações anteriores. O elevado teor de açúcar foi necessário para obtenção da concentração alcoólica desejada no vinho e, assim, conferir inibições e toxicidades detectáveis. Nas fermentações com concentração de etanol menor que 6,4% (v v-1) o efeito tóxico ou inibidor não foi detectado. A inibição pelo etanol e por outros componentes foi detectada sobre as leveduras e os resultados mostraram que a redução dos componentes reciclados com a levedura pode melhorar o processo fermentativo.

Determination of the low oxygen limit for several commercial apple cultivars by respiratory quotient breakpoint

Abstract Low oxygen limits for apple ( Malus domestica , Borkh) fruit were determined using modified-atmosphere packaging (MAP) techniques. Fruits were sealed in low density polyethylene (LDPE) packages and placed at 0°C until steady-state respiration was reached. Steady state O 2 and CO 2 partial pressures were varied by altering package thickness, package surface area, and the total fruit weight within the package. Based on measured permeabilities of the LDPE packages to O 2 and CO 2 , package partial pressures were used to determine the gas flux for O 2 and CO 2 for each package, with gas flux rates representing respiratory rates. The effect of O 2 partial pressure on O 2 uptake, CO 2 production, and the respiratory quotient (RQ) was then determined. As the O 2 partial pressure decreased to approximately 2 kPa, RQ remained relatively constant. A marked increase in the RQ (the RQ breakpoint) occurred below 2 kPa O 2 , which was associated with elevated ethanol concentrations. The low O 2 tolerance limit was then estimated for each cultivar as the O 2 level at the RQ breakpoint; these values ranged from 0.7 kPa O 2 for cultivars “Red Delicious” and 0.8 kPa for “Law Rome” to approximately 1.9 kPa for “McIntosh”.

68] Microsomal oxidant radical production and ethanol oxidation

Publisher Summary Rat liver microsomes generate a potent oxidant during electron-transfer reactions initiated by nicotinamide adenine dinucleotide phosphate (NADPH). The oxidant species exhibits the oxidizing power of the hydroxyl radical (·OH) and appears to be formed from H 2 O 2 as precursor. Although a minor pathway of ethanol oxidation compared to alcohol dehydrogenase, the microsomal system assumes greater significance at elevated concentrations of ethanol and is inducible by the chronic consumption of ethanol. Some characteristics and the significance of the microsomal ethanol-oxidizing pathway are described. The mechanism at the molecular level for the oxidation of ethanol by liver microsomes is not clear. Ethanol can react with ·OH to produce acetaldehyde. Ethanol was oxidized by ·OH generated from model systems. Its oxidation by liver microsomes was inhibited by a series of competitive ·OH scavengers. Typical ·OH scavengers were oxidized during NADPH-dependent electron transfer. This chapter describes techniques for assaying the generation of ·OH-like oxidant species by microsomes and for evaluating its role in microsomal ethanol oxidation.