| 1. |
- Mandenius, C. F., et al.
(author)
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Predicting fermentability of wood hydrolyzates with responses from electronic noses
- 1999
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In: Biotechnology progress (Print). - New York, NY, United States : AIChE. - 8756-7938 .- 1520-6033. ; 15:4, s. 617-621
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Journal article (peer-reviewed)abstract
- The fermentability of lignocellulose hydrolyzates have been predicted from the responses of a combination of chemical gas sensors. The hydrolyzates were prepared by dilute-acid hydrolysis of wood from pine, aspen, birch, and spruce. The volatile emission from the hydrolyzates before fermentation was measured, and the sensor array response pattern was compared with the observed fermentability of the hydrolyzates, i.e. with the final ethanol concentration after fermentation and the maximum specific ethanol production rate. Two concentration parameters in the hydrolyzates, furfural and the sum of furfural and 5-(hydroxymethyl)furfural (HMF), were also predicted from the responses. The sensors used were metal oxide semiconductor field effect transistors (MOSFET), tin oxide semiconductor devices, and conductive polymer sensors configured in two sensor arrays. The sensor array response pattern was analyzed by principal component analysis and artificial neural networks. Predictions from artificial neural networks deviated from measured values with less than 15%.The fermentability of lignocellulose hydrolyzates have been predicted from the responses of a combination of chemical gas sensors. The hydrolyzates were prepared by dilute-acid hydrolysis of wood from pine, aspen, birch, and spruce. The volatile emission from the hydrolyzates before fermentation was measured, and the sensor array response pattern was compared with the observed fermentability of the hydrolyzates, i.e. with the final ethanol concentration after fermentation and the maximum specific ethanol production rate. Two concentration parameters in the hydrolyzates, furfural and the sum of furfural and 5-(hydroxymethyl)furfural (HMF), were also predicted from the responses. The sensors used were metal oxide semiconductor field effect transistors (MOSFET), tin oxide semiconductor devices, and conductive polymer sensors configured in two sensor arrays. The sensor array response pattern was analyzed by principal component analysis and artificial neural networks. Predictions from artificial neural networks deviated from measured values with less than 15%.
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| 2. |
- Taherzadeh, Mohammad J, 1965-, et al.
(author)
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Acetic acid-friend or foe in anaerobic batch conversion of glucose to ethanol by Saccharomyces cerevisiae?
- 1997
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In: Chemical Engineering Science. - Oxford, United Kingdom : Elsevier Science Ltd. - 0009-2509. ; 52:15, s. 2653-2659
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Journal article (peer-reviewed)abstract
- The permissible region of growth of Saccharomyces cerevisiae on glucose under anaerobic conditions was determined as a function of both pH and the concentration of added acetic acid to the medium. In the absence of acetic acid, growth was possible at a pH as low as 2.5, whereas a total acetic acid addition of 10 gl-1 increased the minimum allowable pH for growth to 4.5. The results showed that the concentration of the undissociated form of acetic acid should not exceed 5 gl-1 in the medium for growth to occur. The addition of acetic acid had a profound effect on growth energetics, thereby leading to an increased ethanol yield on glucose. At a concentration of 3.3 gl-1 of undissociated acetic acid, the ethanol yield was 20% higher than without added acetic acid. Furthermore, the biomass and glycerol yields decreased by 45 and 33%, respectively.The permissible region of growth of Saccharomyces cerevisiae on glucose under anaerobic conditions was determined as a function of both pH and the concentration of added acetic acid to the medium. In the absence of acetic acid, growth was possible at a pH as low as 2.5, whereas a total acetic acid addition of 10 g l-1 increased the minimum allowable pH for growth to 4.5. The results showed that the concentration of the undissociated form of acetic acid should not exceed 5 g l-1 in the medium for growth to occur. The addition of acetic acid had a profound effect on growth energetics, thereby leading to an increased ethanol yield on glucose. At a concentration of 3.3 g l-1 of undissociated acetic acid, the ethanol yield was 20% higher than without added acetic acid. Furthermore, the biomass and glycerol yields decreased by 45 and 33%, respectively.
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| 3. |
- Taherzadeh, Mohammad J, 1965-, et al.
(author)
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Characterization and Fermentation of Dilute-Acid Hydrolyzates from Wood
- 1997
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In: Industrial and Engineering Chemistry Research. - : American Chemical Society. - 0888-5885 .- 1520-5045. ; 36:11, s. 4659-4665
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Journal article (peer-reviewed)abstract
- Dilute-acid hydrolyzates from alder, aspen, birch, willow, pine, and spruce were fermented without prior detoxification. The hydrolyzates were prepared by a one-stage hydrolysis process using sulfuric acid (5 g/L) at temperatures between 188 and 234°C and with a holding time of 7 min. The fermentations were carried out anaerobically by Saccharomyces cerevisiae (10 g of d.w./L) at a temperature of 30°C and an initial pH of 5.5. The fermentabilities were quite different for the different wood species, and only hydrolyzates of spruce produced at 188 and 198°C hydrolyzates of pine produced at 188°C, and hydrolyzates of willow produced at 198°C could be completely fermented within 24 h. From the sum of the concentrations of the known inhibitors furfural and 5-(hydroxymethyl)furfural (HMF), a good prediction of the maximum ethanol production rate could be obtained, regardless of the origin of the hydrolyzate. Furthermore, in hydrolyzates that fermented well, furfural and HMF were found to be taken up and converted by the yeast, concomitant with the uptake of glucose.
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| 4. |
- Taherzadeh, Mohammad J, 1965-, et al.
(author)
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Conversion of dilute-acid hydrolyzates of spruce and birch to ethanol by fed-batch fermentation
- 1999
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In: Bioresource Technology. - Exeter, United Kingdom : Elsevier Sci Ltd. - 0960-8524 .- 1873-2976. ; 69:1, s. 59-66
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Journal article (peer-reviewed)abstract
- Fermentation techniques for conversion of dilute acid hydrolyzates were examined. Batch and fed-batch fermentations of hydrolyzates from spruce and birch woods were made in a lab-scale (3.31) anaerobic bioreactor using the yeast Saccharomyces cerevisiae. The spruce and birch hydrolyzates contained high initial concentrations of furfural (2.2 and 5.7 g/l) and 5-hydroxymethylfurfural (HMF, 7.3 and 2.4 g/l), and were found to be strongly inhibiting to the yeast strain used in this study. Fermentation of the hydrolyzates was not possible using a batch mode of operation. However, using a fed-batch technique with a suitably adjusted feed rate, it was found possible to completely ferment the glucose and mannose sugars in both hydrolyzates. Most of the furfural (90%), and part of the HMF (40-70%), present in the hydrolyzates was converted during the fed-batch operation. It is suggested that the success of the fed-batch operation is related to the conversion of furfural and HMF.Fermentation techniques for conversion of dilute acid hydrolyzates were examined. Batch and fed-batch fermentations of hydrolyzates from spruce and birch woods were made in a lab-scale (3.31) anaerobic bioreactor using the yeast Saccharomyces cerevisiae. The spruce and birch hydrolyzates contained high initial concentrations of furfural (2.2 and 5.7 g/l) and 5-hydroxymethylfurfural (HMF, 7.3 and 2.4 g/l), and were found to be strongly inhibiting to the yeast strain used in this study. Fermentation of the hydrolyzates was not possible using a batch mode of operation. However, using a fed-batch technique with a suitably adjusted feed rate, it was found possible to completely ferment the glucose and mannose sugars in both hydrolyzates. Most of the furfural (90%), and part of the HMF (40-70%), present in the hydrolyzates was converted during the fed-batch operation. It is suggested that the success of the fed-batch operation is related to the conversion of furfural and HMF.
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| 5. |
- Taherzadeh, Mohammad J, 1965-, et al.
(author)
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Conversion of furfural in aerobic and anaerobic batch fermentation of glucose by Saccharomyces cerevisiae
- 1999
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In: Journal of Bioscience and Bioengineering. - : Society of Fermentation and Bioengineering. - 1389-1723 .- 1347-4421. ; 87:2, s. 169-174
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Journal article (peer-reviewed)abstract
- The effect of furfural on aerobic and anaerobic batch cultures of Saccharomyces cerevisiae CBS 8066 growing on glucose was investigated. Furfural was found to decrease both the specific growth rate and ethanol production rate after pulse additions in both anaerobic and aerobic batch cultures. The specific growth rate remained low until the furfural had been completely consumed, and then increased somewhat, but not to the initial value. The CO2 evolution rate decreased to about 35% of the value before the addition of 4 g·l-1 furfural, in both aerobic and anaerobic fermentations. The decrease of the CO2 evolution rate was rapid at first, and then a more gradual decrease was observed. The furfural was converted mainly to furfuryl alcohol, with a specific conversion rate of 0.6 (± 0.03) g (furfural)·g- 1 (biomass)·h-1 by exponentially growing cells. However, the conversion rate of furfural by cells in the stationary phase was much lower. A previously unidentified compound was detected during the conversion of furfural. This compound was characterized by mass spectrometry and it is suggested that it is formed from furfural and pyruvate.
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| 6. |
- Taherzadeh, Mohammad J, 1965-
(author)
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Ethanol from lignocellulose : physiological effects of inhibitors and fermentation strategies
- 1999
-
Doctoral thesis (other academic/artistic)abstract
- Fermentative ethanol production from dilute-acid hydrolyzates of wood using the yeast Saccharomyces cerevisiae was investigated. Of known inhibitors in hydrolyzates, acetic acid, furfural and hydroxymethyl furfural (HMF) were found in the highest concentrations (up to about 10 g/l). Physiological effects of these inhibitors were studied in synthetic media. Based on these studies, on-line control of fed-batch cultivation for in-situ detoxification of the hydrolyzates was subsequently developed. The effect of acetic acid on yeast was found to strongly depend on pH. At concentration of undissociated acetic acid higher than 5 g/l, growth stopped. However, presence of the acid in the medium at low concentration (e.g. 1 g/l) increased ethanol yield and decreased the formation of fermentation by-products. Furfural (4 g/l) severely decreases the specific growth rate of S. cerevisiae in pulse addition experiments. However, the yeast was able to convert furfural to less inhibiting products, mainly by reduction to furfuryl alcohol, with a specific conversion rate of 0.6 g/g·h. A previously unidentified metabolite was also found and was characterized by mass spectrometry. Presumably, the metabolite was formed from pyruvate and furfural. HMF is less inhibiting to yeast than furfural, but remains in the medium for about 4 times longer than furfural due to a lower conversion rate. The yeast converts HMF mainly to hydroxymethyl-furfuryl alcohol and a newly identified compound probably formed from HMF and acetaldehyde. Fed-batch fermentation was suggested as a suitable mode of operation for fermenting dilute-acid hydrolyzates from the physiological studies of the inhibitors. With a suitable feed rate, it was possible to ferment also severely inhibiting spruce and birch hydrolyzates using fed-batch operation without any pretreatment of the hydrolyzates. However, the feed rate was critical in order to obtain a successful operation. A simple feedback control strategy was therefore developed, allowing the feed rate to be determined on-line, without any other input variable than the measured carbon dioxide evolution rate.
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| 7. |
- Taherzadeh, Mohammad J, 1965-, et al.
(author)
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The effects of pantothenate deficiency and acetate addition on anaerobic batch fermentation of glucose by Saccharomyces cerevisiae
- 1996
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In: Applied Microbiology and Biotechnology. - : Springer. - 0175-7598 .- 1432-0614. ; 46:2, s. 176-182
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Journal article (peer-reviewed)abstract
- Physiological effects of deficiency of pantothenate, a necessary precursor in the synthesis of coenzyme A, were studied using the yeast strain Saccharomyces cerevisiae CBS 8066. Cells were grown on defined media in anaerobic batch cultures with glucose (50 g/l) as the carbon and energy source. Batch cultures containing more than 60 μg/l pantothenate showed no significant differences with respect to growth rates and product yields. However, with an initial pantothenate concentration of 30 μg/l, the average glucose consumption rate was 50% lower than in rich medium and, at even lower concentrations of pantothenate, the culture did not consume all the glucose in the medium. Furthermore, pantothenate deficiency caused the acetate and pyruvate yields to increase and the biomass yield to decrease, compared to the yields in pantothenate-rich medium. The increased acetate formation could be counteracted by initial addition of acetate to the medium, and thereby the glycerol yield could be decreased. An initial addition of acetate of 1.6 g/l to pantothenate-deficient medium (30 μg/l) caused a 35% decrease in glycerol yield and a 6% increase in ethanol yield. Furthermore, the time required for complete conversion of the glucose decreased by 40%. Acetate addition affected the acetate and glycerol yields in a similar way in pantothenate-rich medium (1000 μg/l) also.
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