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We previously observed that as glucose is completely exhausted during ethanol fermentation, the dissolved carbon dioxide (DCO2) level in the fermenter will suddenly decline. This observation was implemented to design and develop a DCO2‐driven‐and‐controlled repeated batch fermentation process for ethanol production. The process was tested at four different glucose concentrations (~150 g/L, ~200 g/L, ~250 g/L, and ~300 g/L), and each glucose concentration was controlled under three respective DCO2 control levels (without DCO2 control, and DCO2 controlled at either 1000 mg/L or 750 mg/L). The results show that reported process features complete glucose utilization and is self‐driven. For glucose concentration less than 200 g/L, ~41%‐50% of fermentation time per batch was saved during the repeated batch operation. It took 12.1 ± 1.1 hours‐14.9 ± 1.9 hours to complete a batch with glucose feed at ~250 g/L and 21.7 ± 6 hours‐31.5 ± 7 hours to complete a batch with glucose feed at ~300 g/L. The reported process is time saving and stable, but the ethanol yield is ~20% lower than the operation without DCO2 control. Dissolved CO2 control became essential for glucose concentrations greater than 250 g/L if zero glucose discharge in each batch during the operation is desired. [ABSTRACT FROM AUTHOR]

A previously published genome‐scale metabolic model namely iFF708 was modified to depict the metabolic flux distribution within Saccharomyces cerevisiae grown under a redox potential–controlled very high‐gravity condition. The following modifications were made: electron transport chain (ETC) and oxidative phosphorylation, proton gradient and ATP transportation, and malate–aspartate shuttle. With these modifications, this model could describe the experimental data collected from the above‐mentioned ethanol fermentation. As a result, the simulation unveiled that the P/O ratio is critical under microaerobic conditions and the malate–aspartate shuttle is inactivated due to the shortage of electron transport across mitochondria. In other words, the limited supply of oxygen suppresses the functionality of oxidative phosphorylation, tricarboxylic acid (TCA) cycle, and ETC. In terms of the glycolytic pathway, fluxes coming from glucose‐6‐phosphate and pyruvate nodes are insensitive to the changes of fermentation redox potential. As the initial glucose concentration is greater than 250 g/L, the interactive effect between the initial glucose concentration and redox potential level becomes noticeable. [ABSTRACT FROM AUTHOR]

Abstract: Dekkera bruxellensis is continuously changing its status in fermentation processes, ranging from a contaminant or spoiling yeast to a microorganism with potential to produce metabolites of biotechnological interest. In spite of that, several major aspects of its physiology are still poorly understood. As an acetogenic yeast, minimal oxygen concentrations are able to drive glucose assimilation to oxidative metabolism, in order to produce biomass and acetate, with consequent low yield in ethanol. In the present study, we used disulfiram to inhibit acetaldehyde dehydrogenase activity to evaluate the influence of cytosolic acetate on cell metabolism. D. bruxellensis was more tolerant to disulfiram than Saccharomyces cerevisiae and the use of different carbon sources revealed that the former yeast might be able to export acetate (or acetyl‐CoA) from mitochondria to cytoplasm. Fermentation assays showed that acetaldehyde dehydrogenase inhibition re‐oriented yeast central metabolism to increase ethanol production and decrease biomass formation. However, glucose uptake was reduced, which ultimately represents economical loss to the fermentation process. This might be the major challenge for future metabolic engineering enterprises on this yeast. [ABSTRACT FROM AUTHOR]

ABSTRACT High enzyme loading and low productivity are two major issues impeding low cost ethanol production from lignocellulosic biomass. This work applied rapid bioconversion with integrated recycle technology (RaBIT) and extractive ammonia (EA) pretreatment for conversion of corn stover (CS) to ethanol at high solids loading. Enzymes were recycled via recycling unhydrolyzed solids. Enzymatic hydrolysis with recycled enzymes and fermentation with recycled yeast cells were studied. Both enzymatic hydrolysis time and fermentation time were shortened to 24 h. Ethanol productivity was enhanced by two times and enzyme loading was reduced by 30%. Glucan and xylan conversions reached as high as 98% with an enzyme loading of as low as 8.4 mg protein per g glucan. The overall ethanol yield was 227 g ethanol/kg EA-CS (191 g ethanol/kg untreated CS). Biotechnol. Bioeng. 2017;114: 1713-1720. © 2017 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

This study evaluated ethanol fermentation and its correlation with glutathione (GSH) synthesis under various cadmium-conditions with different metal ions and nitrogen sources. We found that corn steep liquor (CSL) and yeast extract have differential roles to play in GSH accumulation in cell even though both of them could alleviate the inhibition by cadmium. The different GSH accumulation in cell resulted from the different contents of metal ions in CSL and yeast extract. Intracellular GSH decreased with increasing calcium concentrations, and high calcium concentrations rendered the yeast more tolerant to cadmium stress than the nitrogen sources did. When the mole ratio of calcium to cadmium was 100:1, yeast tolerated 1000 mmol/L cadmium with no decrease in efficiency in ethanol production. As a result, the use of calcium allowed a significant saving of high-cost nutrient yeast extract with an efficient ethanol production, making the bioconversion of cadmium-containing biomass into ethanol possible. [ABSTRACT FROM AUTHOR]

ABSTRACT Corncob residue as the lignocellulosic biomass accumulated phenolic compounds generated from xylitol production industry. For utilization of this biomass, Zymomonas mobilis ZM4 was tested as the ethanol fermenting strain and presented a better performance of cell growth (2.8 × 108 CFU/mL) and ethanol fermentability (54.42 g/L) in the simultaneous saccharification and fermentation (SSF) than the typical robust strain Saccharomyces cerevisiae DQ1 (cell growth of 2.9 × 107 CFU/mL, ethanol titer of 48.6 g/L). The physiological response of Z. mobilis ZM4 to the twelve typical phenolic compounds derived from lignocellulose was assayed and compared with that of S. cerevisiae DQ1. Z. mobilis ZM4 showed nearly the same tolerance to the phenolic aldehydes with S. cerevisiae DQ1, but the stronger tolerance to the phenolic acids existing in corncob residue (2-furoic acid, p-hydroxybenzoic acid, p-coumaric acid, vanillic acid, ferulic acid, and syringic acid). The tolerance mechanism of Z. mobilis was investigated in terms of inhibitor degradation, cell morphology and membrane permeability under the stress of phenolics using GC-MS, scanning and transmission electron microscopies (SEM and TEM), as well as fluorescent probes. The results reveal that Z. mobilis ZM4 has the capability for in situ detoxification of phenolic aldehydes, and the lipopolysaccharide aggregation on the cell outer membrane of Z. mobilis ZM4 provided the permeable barrier to the attack of phenolic acids. Biotechnol. Bioeng. 2015;112: 1770-1782. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The cost effective production of cellulolytic enzymes and their use for generating higher reducing sugars from lignocellulosic biomass is critical for attaining the commercial viability of lignocellulosic biofuels production. Optimizing the use of locally available agroresidues and natural nutritional alternatives for fungal growth and enzyme production can reduce the cost of enzyme production. In the present work, maximum cellulolytic activity of 30.85 IU/gds was obtained from Trichoderma reesei NCIM 1186 using wheat bran as the substrate and coconut water as the nutritional supplement. The produced cellualse was used for enzymatic saccharification of phosphoric acid pretreated wheat straw. The enzymatic sachharification was optimized through central composite design (CCD) based response surface methodology (RSM). Maximum reducing sugar yields of 371.44 mg/g dry substrate were obtained at 18% (w/v) substrate concentration, 50°C and 24 h of incubation time. Further, the saccharified sugar hydrolysate was fermented using S. cerevisiae NCIM 3215. Maximum ethanol production (2.58% w/v) obtained after 24 h of fermentation at 30°C. © 2015 American Institute of Chemical Engineers Environ Prog, 34: 1243-1248, 2015 [ABSTRACT FROM AUTHOR]

Flocculation is an attractive feature of the yeast Saccharomyces uvarum. The usefulness of its application in the fermentation process comes from the simple separation technique of the yeast cells from the fermentation products. The benefit of the flocculation of S. uvarum is that it keeps the continuous fermentation of ethanol at a certain level as it maintains the yeast inside the bioreactor and prevents it from being washed out with the ethanol. The flocculation behavior of the yeast was studied during the production of ethanol from date syrup. Furthermore, the compatibility of the optimum conditions between flocculation and ethanol fermentation was studied. Three essential parameters were studied during the continuous ethanol production: fermentation temperature, date syrup concentration, and feeding flow rate. The statistical application of central composite design was used to identify the optimum conditions that maintain the flocculation between the yeast cells and prevent it from being washed out with the product. The minimum percentage of washout yeast from the bioreactor (9.15%) was carried out under the following conditions: a temperature of 20°C, an initial date syrup sugar concentration of 6.5% (w/v), and a feeding flow rate of 294 mL h−1. In line with the optimum conditions of the ethanol production, the conditions that gave the best ethanol productivity (7.57 g L−1 h−1) with a minimum washout yeast (19.6%) was found to be a fermentation temperature of 29°C, an initial date syrup sugar concentration of 5.5% (w/v) and a feeding flow rate of 294 mL h−1. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 308-314, 2014 [ABSTRACT FROM AUTHOR]

Raw starch and raw cassava tuber powder were directly and efficiently fermented at elevated temperatures to produce ethanol using the thermotolerant yeast Kluyveromyces marxianus that expresses α-amylase from Aspergillus oryzae as well as α-amylase and glucoamylase from Debaryomyces occidentalis. Among the constructed K. marxianus strains, YRL 009 had the highest efficiency in direct starch fermentation. Raw starch from corn, potato, cassava, or wheat can be fermented at temperatures higher than 40°C. At the optimal fermentation temperature 42°C, YRL 009 produced 66.52 g/L ethanol from 200 g/L cassava starch, which was the highest production among the selected raw starches. This production increased to 79.75 g/L ethanol with a 78.3% theoretical yield (with all cassava starch were consumed) from raw cassava starch at higher initial cell densities. Fermentation was also carried out at 45 and 48°C. By using 200 g/L raw cassava starch, 137.11 and 87.71 g/L sugar were consumed with 55.36 and 32.16 g/L ethanol produced, respectively. Furthermore, this strain could directly ferment 200 g/L nonsterile raw cassava tuber powder (containing 178.52 g/L cassava starch) without additional nutritional supplements to produce 69.73 g/L ethanol by consuming 166.07 g/L sugar at 42°C. YRL 009, which has consolidated bioprocessing ability, is the best strain for fermenting starches at elevated temperatures that has been reported to date. © 2014 American Institute of Chemical Engineers Biotechnol. Prog., 30:338-347, 2014 [ABSTRACT FROM AUTHOR]

Background To operate the fermentation process effectively and efficiently, the kinetic modeling of cell growth and ethanol fermentation is necessary to predict the results of industrial fermentations under the optimized conditions. Results A kinetic study was conducted for glucose utilization for growth of the yeast strain Kluyveromyces sp. IIPE453 and ethanol formation. Effect of temperature, pH and initial glucose concentration on cell growth and ethanol formation was studied. The data obtained experimentally were validated with existing kinetic models for product and/or substrate inhibition. Conclusion Of all the models, the Aiba model for substrate inhibition was found to be the best fit to the experimental data for the growth of Kluyveromyces sp. IIPE453, and the Luong model for product inhibition was found to be the best fit for ethanol formation using Kluyveromyces sp. IIPE453. © 2013 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Engineering industrial microbial strains with inulinase production for developing a consolidated bioprocessing (CBP) strategy is a desirable solution to biofuel production from Jerusalem artichoke tubers. In this study, the integrative vector pFA6a-rDNA-PGK-INU was generated by fusing the 3.3-kb ribosomal DNA fragment with the phosphoglycerate kinase promoter to regulate the expression of the inulinase gene isolated from Kluyveromyces marxianus, which was then integrated into the chromosome of an industrial Saccharomyces cerevisiae strain for ethanol production from Jerusalem artichoke tubers. Compared to the host strain, no significant difference was observed in the growth of the recombinant yeast, but its inulinase production was enhanced: 22.9 versus 10.6 U/mL for aerobic seed cultures and 14.5 versus 10.0 U/mL for ethanol fermentation, which consequently facilitated the CBP process for ethanol production: 72.5 g/L ethanol produced in a fermentation time of 48 h, while only 67.0 g/L ethanol was produced by the host strain in a fermentation time of 60 h. Thus, the ethanol productivity was increased from 1.12 to 1.51 g/L/h, presenting an increase of 34.8%. [ABSTRACT FROM AUTHOR]

To identify the best ensiling process and moisture content for rice grain silage, we determined the effects of additive (i.e. no additive, glucose additive or lactic acid bacteria [ LAB] inoculation), crushing process (non-crushing or crushing) and moisture control (none [13.6%], 20.0, 27.5, 35.0, 42.5 or 50.0% moisture content [in fresh matter, FM]) on rough rice and brown rice. Forage rice harvested at the fully ripe stage was ensiled in small-scale experiments, and the silage was stored for 60 days. Regardless of the use of additives or LAB inoculation, the pH values tended to decrease with increasing moisture content. LAB inoculation and crushing resulted in low pH values, low butyric acid contents, low ethanol contents and high lactic acid contents, and the lactic acid content increased to more than 2.0% in FM at moisture contents of 27.5% and higher. The parameters of fermentation quality ( pH, lactic acid, butyric acid, volatile basic nitrogen and ethanol content) were affected by not only the main effect of additive, crushing process and moisture control but also two-way or three-way interaction effects. LAB inoculation and crushing improved the lactic acid fermentation under lower moisture conditions, that is, 27.5% moisture content. In both rough rice and brown rice, we suggest that the appropriate pretreatment is the combined use of LAB inoculation, crushing process and controlling 27.5% moisture content. [ABSTRACT FROM AUTHOR]

The term “auto-brewery syndrome” has been frequently used to describe patients who show features of alcohol intoxication because of abnormal yeast proliferation after ingesting carbohydrate-rich meals. We present a case of a 3-y-old girl with short bowel syndrome (SBS) who demonstrated signs of alcohol intoxication on repeated occasions. A blood test indicated an ethanol concentration of 15 mmol/l, and cultures from gastric fluid and faeces showed the presence of Candida kefyr . An association was found between the introduction of a carbohydrate-rich fruit drink and the occurrence of symptoms. Conclusion: The possibility of endogenous ethanol fermentation should be considered in patients with SBS and the diagnosis of auto-brewery syndrome added to the differential diagnosis list for D-lactic acidosis. Management includes both antifungal treatment and special diet modification. [ABSTRACT FROM AUTHOR]

Raman spectroscopy as a process analytical technology tool was implemented for the monitoring and control of ethanol fermentation carried out with Saccharomyces cerevisiae. The need for the optimization of bioprocesses such as ethanol production, to increase product yield, enhanced the development of control strategies. The control system developed by the authors utilized noninvasive Raman measurements to avoid possible sterilization problems. Real‐time data analysis was applied using partial least squares regression (PLS) method. With the aid of spectral pretreatment and multivariate data analysis, the monitoring of glucose and ethanol concentration was successful during yeast fermentation with the prediction error of 4.42 g/L for glucose and 2.40 g/L for ethanol. By Raman spectroscopy‐based feedback control, the glucose concentration was maintained at 100 g/L by the automatic feeding of concentrated glucose solution. The control of glucose concentration during fed‐batch fermentation resulted in increased ethanol production. Ethanol yield of 86% was achieved compared to the batch fermentation when 75% yield was obtained. The results show that the use of Raman spectroscopy for the monitoring and control of yeast fermentation is a promising way to enhance process understanding and achieve consistently high production yield. [ABSTRACT FROM AUTHOR]