The influence of air saturation and temperature on continuous citric acid secretion was studied i... more The influence of air saturation and temperature on continuous citric acid secretion was studied in chemostat cultures of Candida oleophila ATCC 20177 (var.). Simultaneous measurements of intra-and extracellular concentration of glucose, citric and isocitric acid confirmed the involvement of a specific active transport system in citrate secretion, favouring citric acid over isocitrate. An optimum air oxygen saturation of 20% and temperature of 30-31ºC were determined for the continuous citric acid secretion. The highest values of citric acid concentration (98 g/L), citrate to isocitrate ratio (33.3:1), volumetric citric productivity (1.8 g/(L x h)), and specific citric acid productivity (0.1 g/(g x h)), were reached at 20% air saturation at a residence time of 54 hrs by the experiment's lowest biomass of 18 g/L. The highest isocitic acid volumetric productivity (55.6 mg/(L x h)) and specific productivity (0.99 mg/(g x h)) were identified at 50%, instead. The fastest citrate excretion rate of the generic product of 0.046 g/(g*h) was found at 30-31ºC. A concentration ratio between extra-and intracellular concentration of citrate of up to 9 was identified. The highest extra-/intracellular ratio of citrate and lowest intracellular concentrations of glucose, citric and isocitric acid were determined at optimum air saturation as a consequence of active citrate export. Citric acid is a tricarboxilic organic acid of industrial importance (Naumenko et al. 2004), which is produced by fermentation using almost exclusively improved strains of the fungus Aspergillus niger in aerobe bioreactors (Saha and Takahashi, 1997; Wieczorek and Brauer, 1997; Wieczorek and Brauer, 1998). The simultaneous synthesis of citric, isocitric (undesirable by-product) and other organic acids by yeasts was extensively studied (Akiyama
Abbreviations: R j: Formation rate of the generic product (volumetric productivity), g gluconic a... more Abbreviations: R j: Formation rate of the generic product (volumetric productivity), g gluconic acid/(l x h), gluconic acid concentration (g/l)/RT (h), g/(l x h) m p : Specific gluconic acid productivity, [g gluconic acid/(g biomass x h)], Rj [g/(l x h)]/biomass concentration (g/l), g/(g x h) RT: Residence time-hours, [Bioreactor volume (ml)/(medium feeding rate (ml/h) + NaOH feeding rate (ml/h))], h Rs: Glucose consumption rate, g/(l x h), [(g feeding glucose-g consumed glucose)/RT (h)], g/(l x h) Conversion (%): [(g consumed glucose/g feeding glucose) x 100], dilution of medium glucose by NaOH feeding was considered in the calculations Yield (%): [(g gluconic acid/g feeding glucose) x 100] Selectivity (%): [(g gluconic acid/g consumed glucose) x 100] New alternative processes for the continuous production of gluconic acid by Aureobasidium pullulans, using biomass retention by cell immobilization or cross over filtration, are described in the present work. 315 g/l gluconic acid was continuously produced in chemostat cultures at 21 hrs residence time without any biomass retention. 260 g/l gluconic acid was produced in fluidized bed reactor at 21 hrs residence time. The support carrier was overgrown resulting in limitations of oxygen transfer towards the inner layers of immobilized biomass. 375 g/l gluconic acid was produced under continuous cultivation at 22 hrs of residence time with a formation rate for the generic product of 17 g/(l x h) and a specific gluconic acid productivity of only 0.74 g/(g x h), using biomass retention by cross over filtration. 370 g/l were obtained at 19 hrs RT and 100% conversion with 25 g/l biomass and a formation rate of 19 g/(l x h). At 100% conversion, a selectivity of only 78% was determined at
Carbon atom Carbon atom is most important and abundant constituent of existing and new generated ... more Carbon atom Carbon atom is most important and abundant constituent of existing and new generated biological mater and biomass and the basis of all forms of life on earth. It is involved in the composition and construction of organic micro-and macromolecules, cells and living organisms, storage molecules, fossils, fossil fuels, biofuels and energy resources of living and nonliving organic matter. Initially originated from atmospheric carbon dioxide, it is absorbed and incorporated into organic molecules by photosynthetic plants and microorganisms through photosynthetic processes to form glucose and other less or more complex organic molecules, enabling and sustaining life on Earth. A semantic part of CO2 has been captured, trapped and immobilized in various forms of fossils, not participating in biogeochemical carbon cycles for millions of years, or is dissolved in oceans. Carbon sources is also one of most important parameters, strongly influencing microbial growth and the accumulation of cellular metabolites, fermentation technologies, process economics and feasibility of industrial production. Advanced developments in recombinant technologies, such as metabolic and genetic engineering, systems and synthetic biology, as well as in bioengineering, biotechnology, industrial microbiology and fermentation technology will expand the opportunities of literally unseen microbial world.
Since early human history and existence energy rich plants, wood and forest cellulosic material h... more Since early human history and existence energy rich plants, wood and forest cellulosic material have been used for fire, light, heating, cooking and other daily activities. Fossil energy was the foundation of our modern society and industrialization since last two centuries, while exploration and exploitation of oil reserves and petrochemistry have largely shaped 20th century. Increasing concerns on environmental pollution, accelerated global warming, and global climate changes, continuing world's crude oil (fossil fuels) consumption and depletion, as well as energy security and energy crisis caused by daily burning large amounts of fossil fuels, led to the attraction, search and development of renewable, carbon-neutral, economically viable alternative energy sources, such as biofuels, slowly displacing petroleum fuels. In continuously growing human population reaching about 10 billion in 2050, various renewable energy sources are promoted and developed, to ensure rising energy demands in a world running out of fossil energy sources. Biofuels are produced from any kind of available biomass and categorized based on utilized carbon resources into first-, second-and third-generation. Nevertheless, biofuels' future outlook is though beset by uncertainty. Hereby, various issues and concerns related to fossils and renewable biofuels are described and analyzed in present review article.
Little is known about the regulatory mechanisms for citric acid production by different yeast. It... more Little is known about the regulatory mechanisms for citric acid production by different yeast. It is suggested the important role of iron ions in this process; iron is the integral component of many metalloenzymes; such as aconitate-hydratase, catalase, peroxidases and components of mitochondrial electron transfer chain. The response of citric acid metabolism to different iron concentrations was studied with ethanol-and glucose-grown yeast; the emphasis was focused on the physiological parameters of yeast growth and citric acid production. The effect of iron on citric acid production by yeasts has been shown to appear in a variable profile when grown on different carbon sources – glucose and ethanol. It was shown, that increased iron promoted growth on the medium containing glucose; but citric acid production decreased with an increase in iron concentration. As contrast, yeast grown on ethanol required the sufficient iron supplementation for citric acid production. The enzyme activi...
In the present work, the possibility of using glycerol and glycerol-containing waste from biodies... more In the present work, the possibility of using glycerol and glycerol-containing waste from biodiesel manufacture as a carbon and energy source for microbiological production of citric acid was studied. Acid-formation ability on selective media was preliminary tested for 66 yeast strains of different genera (Candida, Pichia, Saccharomyces, Torulopsis, and Yarrowia). Under growth limitation by nitrogen source, 41 strains belonging mainly to the species Yarrowia lipolytica were found to excrete organic acids to the culture broth. In contrast, 25 strains of the genera Debaryomyces, Candida, Pichiа, Saccharomyces and Torulopsis did not show acid excretion. Among the 41 acid-producing strains, the wild strain Y. lipolytica VKM Y-2373 and the mutant strain Y. lipolytica N 15 exhibited the highest ability to accumulate citric acid in the culture broth. The production of citric acid by these two strains was studied as a function of the medium pH, degree of aeration and the concentration of gl...
Little is known about the regulatory mechanisms for citric acid production by different yeast. It... more Little is known about the regulatory mechanisms for citric acid production by different yeast. It is suggested the important role of iron ions in this process; iron is the integral component of many metalloenzymes; such as aconitate-hydratase, catalase, peroxidases and components of mitochondrial electron transfer chain. The response of citric acid metabolism to different iron concentrations was studied with ethanol- and glucose-grown yeast; the emphasis was focused on the physiological parameters of yeast growth and citric acid production. The effect of iron on citric acid production by yeasts has been shown to appear in a variable profile when grown on different carbon sources - glucose and ethanol. It was shown, that increased iron promoted growth on the medium containing glucose; but citric acid production decreased with an increase in iron concentration. As contrast, yeast grown on ethanol required the sufficient iron supplementation for citric acid production. The enzyme activ...
The application of a new developed process for the continuous production of gluconic acid using a... more The application of a new developed process for the continuous production of gluconic acid using a cascade of two bioreactors in a continuous process is shown reaching the highest concentration of gluconic acid described in the literature for continuous culture fermentation. Very high gluconic acid concentrations of 272-308 g/l have been achieved under continuous cultivation of free-growing cells of Aureobasidium pullulans in the first bioreactor at residence times (RT) between 19.5 and 24 h with formation rates for the generic product between 12.7 and 13.9 g/(l h). Gluconic acid, 350-370 g/l, was continuously reached in the second bioreactor at a total RT of 30.8-37 h with R (j) of 9.2-12 g/(l h). The highest specific gluconic acid production (m (p)) of 3.6 g/(g h) was found in the first bioreactor at the lowest RT of 19.5 h. The highest selectivity of 93.6% was determined in the first bioreactor as well. Complete glucose consumption was obtained at 37 h total residence time in the second bioreactor. Gluconic acid, 433 g/l, was continuously produced in the second bioreactor at a total RT of 37 h.
The effect of air saturation on citric acid production in batch, repeated batch and chemostat cul... more The effect of air saturation on citric acid production in batch, repeated batch and chemostat cultures has been studied. It was shown that, under continuous fermentation (chemostat mode), the highest concentration of citric acid equal of 98 g/l was produced at 20% of air saturation. In contrary to continuous fermentation, displaying an optimum at 20%, 80% air saturation yielded higher values in repeated batch fermentation process. 167 g/l citric acid were produced continuously with the fill and drain technique at 4.85 days, at 80% air saturation, compared with 157.6 g/l achieved within 5.4 days at 20%. Under repeated batch fermentation, the formation rate of the generic product (Rj) as well as the specific citric acid productivity (mp) reached a maximum of 1.283 g/(l x hr) at 4.01 days and of 0.0375 g/(g x hr) at 4.58 days, respectively. The glucose consumption rate (Rx) reached a maximum value of 3.33 g/(l x hr) entering stationary phase after 2.56 days at a glucose concentration of 131.2 g/l.
New processes have been previously described for the continuous and discontinuous production of g... more New processes have been previously described for the continuous and discontinuous production of gluconic
acid by Aureobasidium pullulans (de bary) Arnaud. Little is known about the regulatory mechanisms of gluconic acid
production by A. pullulans. The response of growth and gluconic acid metabolism to a variable profile of iron concentrations was studied with A. pullulans in batch and chemostat cultures. A surprisingly high optimum N-dependent iron ion concentration in the feed medium, in the range between 0.5 mM and 3.0 mM Fe (optimum 1-2 mM),
was found to be particular requirement for economically
profitable continuous production of gluconic acid with 3 g/l NH4Cl. Increased iron concentration promoted growth on defined glucose medium. 223.3 g/l gluconic acid were continuously produced at a formation rate of the generic product (Rj) of 16.8 g/(lh) and a specific gluconic acid productivity (m) of 2.5 g/(gh) at 13 h residence time (RT) with 1mM iron, compared with 182 g/l reached at 0.1 mM. The product selectivity (product yield based on glucose) increased continuously by raising iron concentration following a saturation curve, reaching a maximum
of about 98% (mol/mol) at 2 mM Fe and 76.2% conversion, compared with only 84.3% determined at 0.1 mM. The process is not obligatory growth limiting or growth related
and residual nitrogen was found in all of continuous
experiments, e.g. 197 mg/l of nitrogen at 0.1 mM and 201 mg/l at 2 mM of iron.
By extensive microbial screening, about 50 strains with the ability to secrete gluconic acid were... more By extensive microbial screening, about 50 strains with the ability to secrete gluconic acid were isolated from wild flowers. The strains belong to the yeast-like mould Aureobasidium pullulans (de Bary) Arnaud. In shake flask experiments, gluconic acid concentrations between 23 and 140 g/l were produced
within 2 days using a mineral medium. In batch experiments, various important fermentation parameters influencing gluconic acid production by A. pullulans isolate 70 (DSM 7085) were identified. Continuous production of gluconic acid with free-growing cells of the isolated yeast-like microorganisms was studied. About 260 g/l gluconic acid at total glucose conversion could be achieved using continuous stirred tank reactors in defined media with residence times (RT) of about 26 h. The
highest space-time-yield of 19.3 g/(l h) with a gluconic
acid concentration of 207.5 g/l was achieved with a RT of
10.8 h. The possibility of gluconic acid production with
biomass retention by immobilised cells on porous sinter
glass is discussed. The new continuous gluconate fermentation
process provides significant advantages over traditional discontinuous operation employing Aspergillus niger. The aim of this work was the development of a continuous fermentation process for the production of gluconic acid. Process control becomes easier, offering constant product quality and quantity.
The influence of air saturation and temperature on continuous citric acid secretion was studied i... more The influence of air saturation and temperature on continuous citric acid secretion was studied in chemostat cultures of Candida oleophila ATCC 20177 (var.). Simultaneous measurements of intra-and extracellular concentration of glucose, citric and isocitric acid confirmed the involvement of a specific active transport system in citrate secretion, favouring citric acid over isocitrate. An optimum air oxygen saturation of 20% and temperature of 30-31ºC were determined for the continuous citric acid secretion. The highest values of citric acid concentration (98 g/L), citrate to isocitrate ratio (33.3:1), volumetric citric productivity (1.8 g/(L x h)), and specific citric acid productivity (0.1 g/(g x h)), were reached at 20% air saturation at a residence time of 54 hrs by the experiment's lowest biomass of 18 g/L. The highest isocitic acid volumetric productivity (55.6 mg/(L x h)) and specific productivity (0.99 mg/(g x h)) were identified at 50%, instead. The fastest citrate excretion rate of the generic product of 0.046 g/(g*h) was found at 30-31ºC. A concentration ratio between extra-and intracellular concentration of citrate of up to 9 was identified. The highest extra-/intracellular ratio of citrate and lowest intracellular concentrations of glucose, citric and isocitric acid were determined at optimum air saturation as a consequence of active citrate export. Citric acid is a tricarboxilic organic acid of industrial importance (Naumenko et al. 2004), which is produced by fermentation using almost exclusively improved strains of the fungus Aspergillus niger in aerobe bioreactors (Saha and Takahashi, 1997; Wieczorek and Brauer, 1997; Wieczorek and Brauer, 1998). The simultaneous synthesis of citric, isocitric (undesirable by-product) and other organic acids by yeasts was extensively studied (Akiyama
Abbreviations: R j: Formation rate of the generic product (volumetric productivity), g gluconic a... more Abbreviations: R j: Formation rate of the generic product (volumetric productivity), g gluconic acid/(l x h), gluconic acid concentration (g/l)/RT (h), g/(l x h) m p : Specific gluconic acid productivity, [g gluconic acid/(g biomass x h)], Rj [g/(l x h)]/biomass concentration (g/l), g/(g x h) RT: Residence time-hours, [Bioreactor volume (ml)/(medium feeding rate (ml/h) + NaOH feeding rate (ml/h))], h Rs: Glucose consumption rate, g/(l x h), [(g feeding glucose-g consumed glucose)/RT (h)], g/(l x h) Conversion (%): [(g consumed glucose/g feeding glucose) x 100], dilution of medium glucose by NaOH feeding was considered in the calculations Yield (%): [(g gluconic acid/g feeding glucose) x 100] Selectivity (%): [(g gluconic acid/g consumed glucose) x 100] New alternative processes for the continuous production of gluconic acid by Aureobasidium pullulans, using biomass retention by cell immobilization or cross over filtration, are described in the present work. 315 g/l gluconic acid was continuously produced in chemostat cultures at 21 hrs residence time without any biomass retention. 260 g/l gluconic acid was produced in fluidized bed reactor at 21 hrs residence time. The support carrier was overgrown resulting in limitations of oxygen transfer towards the inner layers of immobilized biomass. 375 g/l gluconic acid was produced under continuous cultivation at 22 hrs of residence time with a formation rate for the generic product of 17 g/(l x h) and a specific gluconic acid productivity of only 0.74 g/(g x h), using biomass retention by cross over filtration. 370 g/l were obtained at 19 hrs RT and 100% conversion with 25 g/l biomass and a formation rate of 19 g/(l x h). At 100% conversion, a selectivity of only 78% was determined at
Carbon atom Carbon atom is most important and abundant constituent of existing and new generated ... more Carbon atom Carbon atom is most important and abundant constituent of existing and new generated biological mater and biomass and the basis of all forms of life on earth. It is involved in the composition and construction of organic micro-and macromolecules, cells and living organisms, storage molecules, fossils, fossil fuels, biofuels and energy resources of living and nonliving organic matter. Initially originated from atmospheric carbon dioxide, it is absorbed and incorporated into organic molecules by photosynthetic plants and microorganisms through photosynthetic processes to form glucose and other less or more complex organic molecules, enabling and sustaining life on Earth. A semantic part of CO2 has been captured, trapped and immobilized in various forms of fossils, not participating in biogeochemical carbon cycles for millions of years, or is dissolved in oceans. Carbon sources is also one of most important parameters, strongly influencing microbial growth and the accumulation of cellular metabolites, fermentation technologies, process economics and feasibility of industrial production. Advanced developments in recombinant technologies, such as metabolic and genetic engineering, systems and synthetic biology, as well as in bioengineering, biotechnology, industrial microbiology and fermentation technology will expand the opportunities of literally unseen microbial world.
Since early human history and existence energy rich plants, wood and forest cellulosic material h... more Since early human history and existence energy rich plants, wood and forest cellulosic material have been used for fire, light, heating, cooking and other daily activities. Fossil energy was the foundation of our modern society and industrialization since last two centuries, while exploration and exploitation of oil reserves and petrochemistry have largely shaped 20th century. Increasing concerns on environmental pollution, accelerated global warming, and global climate changes, continuing world's crude oil (fossil fuels) consumption and depletion, as well as energy security and energy crisis caused by daily burning large amounts of fossil fuels, led to the attraction, search and development of renewable, carbon-neutral, economically viable alternative energy sources, such as biofuels, slowly displacing petroleum fuels. In continuously growing human population reaching about 10 billion in 2050, various renewable energy sources are promoted and developed, to ensure rising energy demands in a world running out of fossil energy sources. Biofuels are produced from any kind of available biomass and categorized based on utilized carbon resources into first-, second-and third-generation. Nevertheless, biofuels' future outlook is though beset by uncertainty. Hereby, various issues and concerns related to fossils and renewable biofuels are described and analyzed in present review article.
Little is known about the regulatory mechanisms for citric acid production by different yeast. It... more Little is known about the regulatory mechanisms for citric acid production by different yeast. It is suggested the important role of iron ions in this process; iron is the integral component of many metalloenzymes; such as aconitate-hydratase, catalase, peroxidases and components of mitochondrial electron transfer chain. The response of citric acid metabolism to different iron concentrations was studied with ethanol-and glucose-grown yeast; the emphasis was focused on the physiological parameters of yeast growth and citric acid production. The effect of iron on citric acid production by yeasts has been shown to appear in a variable profile when grown on different carbon sources – glucose and ethanol. It was shown, that increased iron promoted growth on the medium containing glucose; but citric acid production decreased with an increase in iron concentration. As contrast, yeast grown on ethanol required the sufficient iron supplementation for citric acid production. The enzyme activi...
In the present work, the possibility of using glycerol and glycerol-containing waste from biodies... more In the present work, the possibility of using glycerol and glycerol-containing waste from biodiesel manufacture as a carbon and energy source for microbiological production of citric acid was studied. Acid-formation ability on selective media was preliminary tested for 66 yeast strains of different genera (Candida, Pichia, Saccharomyces, Torulopsis, and Yarrowia). Under growth limitation by nitrogen source, 41 strains belonging mainly to the species Yarrowia lipolytica were found to excrete organic acids to the culture broth. In contrast, 25 strains of the genera Debaryomyces, Candida, Pichiа, Saccharomyces and Torulopsis did not show acid excretion. Among the 41 acid-producing strains, the wild strain Y. lipolytica VKM Y-2373 and the mutant strain Y. lipolytica N 15 exhibited the highest ability to accumulate citric acid in the culture broth. The production of citric acid by these two strains was studied as a function of the medium pH, degree of aeration and the concentration of gl...
Little is known about the regulatory mechanisms for citric acid production by different yeast. It... more Little is known about the regulatory mechanisms for citric acid production by different yeast. It is suggested the important role of iron ions in this process; iron is the integral component of many metalloenzymes; such as aconitate-hydratase, catalase, peroxidases and components of mitochondrial electron transfer chain. The response of citric acid metabolism to different iron concentrations was studied with ethanol- and glucose-grown yeast; the emphasis was focused on the physiological parameters of yeast growth and citric acid production. The effect of iron on citric acid production by yeasts has been shown to appear in a variable profile when grown on different carbon sources - glucose and ethanol. It was shown, that increased iron promoted growth on the medium containing glucose; but citric acid production decreased with an increase in iron concentration. As contrast, yeast grown on ethanol required the sufficient iron supplementation for citric acid production. The enzyme activ...
The application of a new developed process for the continuous production of gluconic acid using a... more The application of a new developed process for the continuous production of gluconic acid using a cascade of two bioreactors in a continuous process is shown reaching the highest concentration of gluconic acid described in the literature for continuous culture fermentation. Very high gluconic acid concentrations of 272-308 g/l have been achieved under continuous cultivation of free-growing cells of Aureobasidium pullulans in the first bioreactor at residence times (RT) between 19.5 and 24 h with formation rates for the generic product between 12.7 and 13.9 g/(l h). Gluconic acid, 350-370 g/l, was continuously reached in the second bioreactor at a total RT of 30.8-37 h with R (j) of 9.2-12 g/(l h). The highest specific gluconic acid production (m (p)) of 3.6 g/(g h) was found in the first bioreactor at the lowest RT of 19.5 h. The highest selectivity of 93.6% was determined in the first bioreactor as well. Complete glucose consumption was obtained at 37 h total residence time in the second bioreactor. Gluconic acid, 433 g/l, was continuously produced in the second bioreactor at a total RT of 37 h.
The effect of air saturation on citric acid production in batch, repeated batch and chemostat cul... more The effect of air saturation on citric acid production in batch, repeated batch and chemostat cultures has been studied. It was shown that, under continuous fermentation (chemostat mode), the highest concentration of citric acid equal of 98 g/l was produced at 20% of air saturation. In contrary to continuous fermentation, displaying an optimum at 20%, 80% air saturation yielded higher values in repeated batch fermentation process. 167 g/l citric acid were produced continuously with the fill and drain technique at 4.85 days, at 80% air saturation, compared with 157.6 g/l achieved within 5.4 days at 20%. Under repeated batch fermentation, the formation rate of the generic product (Rj) as well as the specific citric acid productivity (mp) reached a maximum of 1.283 g/(l x hr) at 4.01 days and of 0.0375 g/(g x hr) at 4.58 days, respectively. The glucose consumption rate (Rx) reached a maximum value of 3.33 g/(l x hr) entering stationary phase after 2.56 days at a glucose concentration of 131.2 g/l.
New processes have been previously described for the continuous and discontinuous production of g... more New processes have been previously described for the continuous and discontinuous production of gluconic
acid by Aureobasidium pullulans (de bary) Arnaud. Little is known about the regulatory mechanisms of gluconic acid
production by A. pullulans. The response of growth and gluconic acid metabolism to a variable profile of iron concentrations was studied with A. pullulans in batch and chemostat cultures. A surprisingly high optimum N-dependent iron ion concentration in the feed medium, in the range between 0.5 mM and 3.0 mM Fe (optimum 1-2 mM),
was found to be particular requirement for economically
profitable continuous production of gluconic acid with 3 g/l NH4Cl. Increased iron concentration promoted growth on defined glucose medium. 223.3 g/l gluconic acid were continuously produced at a formation rate of the generic product (Rj) of 16.8 g/(lh) and a specific gluconic acid productivity (m) of 2.5 g/(gh) at 13 h residence time (RT) with 1mM iron, compared with 182 g/l reached at 0.1 mM. The product selectivity (product yield based on glucose) increased continuously by raising iron concentration following a saturation curve, reaching a maximum
of about 98% (mol/mol) at 2 mM Fe and 76.2% conversion, compared with only 84.3% determined at 0.1 mM. The process is not obligatory growth limiting or growth related
and residual nitrogen was found in all of continuous
experiments, e.g. 197 mg/l of nitrogen at 0.1 mM and 201 mg/l at 2 mM of iron.
By extensive microbial screening, about 50 strains with the ability to secrete gluconic acid were... more By extensive microbial screening, about 50 strains with the ability to secrete gluconic acid were isolated from wild flowers. The strains belong to the yeast-like mould Aureobasidium pullulans (de Bary) Arnaud. In shake flask experiments, gluconic acid concentrations between 23 and 140 g/l were produced
within 2 days using a mineral medium. In batch experiments, various important fermentation parameters influencing gluconic acid production by A. pullulans isolate 70 (DSM 7085) were identified. Continuous production of gluconic acid with free-growing cells of the isolated yeast-like microorganisms was studied. About 260 g/l gluconic acid at total glucose conversion could be achieved using continuous stirred tank reactors in defined media with residence times (RT) of about 26 h. The
highest space-time-yield of 19.3 g/(l h) with a gluconic
acid concentration of 207.5 g/l was achieved with a RT of
10.8 h. The possibility of gluconic acid production with
biomass retention by immobilised cells on porous sinter
glass is discussed. The new continuous gluconate fermentation
process provides significant advantages over traditional discontinuous operation employing Aspergillus niger. The aim of this work was the development of a continuous fermentation process for the production of gluconic acid. Process control becomes easier, offering constant product quality and quantity.
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Papers by Dr. Savas Anastassiadis
acid by Aureobasidium pullulans (de bary) Arnaud. Little is known about the regulatory mechanisms of gluconic acid
production by A. pullulans. The response of growth and gluconic acid metabolism to a variable profile of iron concentrations was studied with A. pullulans in batch and chemostat cultures. A surprisingly high optimum N-dependent iron ion concentration in the feed medium, in the range between 0.5 mM and 3.0 mM Fe (optimum 1-2 mM),
was found to be particular requirement for economically
profitable continuous production of gluconic acid with 3 g/l NH4Cl. Increased iron concentration promoted growth on defined glucose medium. 223.3 g/l gluconic acid were continuously produced at a formation rate of the generic product (Rj) of 16.8 g/(lh) and a specific gluconic acid productivity (m) of 2.5 g/(gh) at 13 h residence time (RT) with 1mM iron, compared with 182 g/l reached at 0.1 mM. The product selectivity (product yield based on glucose) increased continuously by raising iron concentration following a saturation curve, reaching a maximum
of about 98% (mol/mol) at 2 mM Fe and 76.2% conversion, compared with only 84.3% determined at 0.1 mM. The process is not obligatory growth limiting or growth related
and residual nitrogen was found in all of continuous
experiments, e.g. 197 mg/l of nitrogen at 0.1 mM and 201 mg/l at 2 mM of iron.
within 2 days using a mineral medium. In batch experiments, various important fermentation parameters influencing gluconic acid production by A. pullulans isolate 70 (DSM 7085) were identified. Continuous production of gluconic acid with free-growing cells of the isolated yeast-like microorganisms was studied. About 260 g/l gluconic acid at total glucose conversion could be achieved using continuous stirred tank reactors in defined media with residence times (RT) of about 26 h. The
highest space-time-yield of 19.3 g/(l h) with a gluconic
acid concentration of 207.5 g/l was achieved with a RT of
10.8 h. The possibility of gluconic acid production with
biomass retention by immobilised cells on porous sinter
glass is discussed. The new continuous gluconate fermentation
process provides significant advantages over traditional discontinuous operation employing Aspergillus niger. The aim of this work was the development of a continuous fermentation process for the production of gluconic acid. Process control becomes easier, offering constant product quality and quantity.
acid by Aureobasidium pullulans (de bary) Arnaud. Little is known about the regulatory mechanisms of gluconic acid
production by A. pullulans. The response of growth and gluconic acid metabolism to a variable profile of iron concentrations was studied with A. pullulans in batch and chemostat cultures. A surprisingly high optimum N-dependent iron ion concentration in the feed medium, in the range between 0.5 mM and 3.0 mM Fe (optimum 1-2 mM),
was found to be particular requirement for economically
profitable continuous production of gluconic acid with 3 g/l NH4Cl. Increased iron concentration promoted growth on defined glucose medium. 223.3 g/l gluconic acid were continuously produced at a formation rate of the generic product (Rj) of 16.8 g/(lh) and a specific gluconic acid productivity (m) of 2.5 g/(gh) at 13 h residence time (RT) with 1mM iron, compared with 182 g/l reached at 0.1 mM. The product selectivity (product yield based on glucose) increased continuously by raising iron concentration following a saturation curve, reaching a maximum
of about 98% (mol/mol) at 2 mM Fe and 76.2% conversion, compared with only 84.3% determined at 0.1 mM. The process is not obligatory growth limiting or growth related
and residual nitrogen was found in all of continuous
experiments, e.g. 197 mg/l of nitrogen at 0.1 mM and 201 mg/l at 2 mM of iron.
within 2 days using a mineral medium. In batch experiments, various important fermentation parameters influencing gluconic acid production by A. pullulans isolate 70 (DSM 7085) were identified. Continuous production of gluconic acid with free-growing cells of the isolated yeast-like microorganisms was studied. About 260 g/l gluconic acid at total glucose conversion could be achieved using continuous stirred tank reactors in defined media with residence times (RT) of about 26 h. The
highest space-time-yield of 19.3 g/(l h) with a gluconic
acid concentration of 207.5 g/l was achieved with a RT of
10.8 h. The possibility of gluconic acid production with
biomass retention by immobilised cells on porous sinter
glass is discussed. The new continuous gluconate fermentation
process provides significant advantages over traditional discontinuous operation employing Aspergillus niger. The aim of this work was the development of a continuous fermentation process for the production of gluconic acid. Process control becomes easier, offering constant product quality and quantity.