Production of Butyric Acid from Glucose and Xylose with Immobilized Cells of <Emphasis Type="Italic">Clostridium tyrobutyricum</Emphasis> in a Fibrous-bed Bioreactor

Butyric acid has many applications in chemical, food, and pharmaceutical industries. In the present study, Clostridium tyrobutyricum ATCC 25755 was immobilized in a fibrous-bed bioreactor to evaluate the performance of butyrate production from glucose and xylose. The results showed that the final concentration and yield of butyric acid were 13.70 and 0.46 g g⁻¹, respectively, in batch fermentation when 30 g L⁻¹ glucose was introduced into the bioreactor. Furthermore, high concentration 10.10 g L⁻¹ and yield 0.40 g g⁻¹ of butyric acid were obtained with 25 g L⁻¹ xylose as the carbon source. The immobilized cells of C. tyrobutyricum ensured similar productivity and yield from repeated batch fermentation. In the fed-batch fermentation, the final concentration of butyric acid was further improved to 24.88 g L⁻¹ with one suitable glucose feeding in the fibrous-bed bioreactor. C. tyrobutyricum immobilized in the fibrous-bed bioreactor would provide an economically viable fermentation process to convert the reducing sugars derived from plant biomass into the final bulk chemical (butyric acid).     

Application of a pH Feedback-Controlled Substrate Feeding Method in Lactic Acid Production

Substrate concentration in lactic acid fermentation broth could not be controlled well by traditional feeding methods, including constant, intermittent, and exponential feeding methods, in fed-batch experiments. A simple feedback feeding method based on pH was proposed to control pH and substrate concentration synchronously to enhance lactic acid production in fed-batch culture. As the linear relationship between the consumption amounts of alkali and that of substrate was concluded during lactic acid fermentation, the alkali and substrate in the feeding broth were mixed together proportionally. Thus, the concentration of substrate could be controlled through the adjustment of pH automatically. In the fed-batch lactic acid fermentation with Lactobacillus lactis-11 by this method, the residual glucose concentration in fermentation broth was controlled between 4.1 and 4.9 g L⁻¹, and the highest concentration of lactic acid, maximum cell dry weight, volumetric productivity of lactic acid, and yield were 96.3 g L⁻¹, 4.7 g L⁻¹, 1.9 g L⁻¹ h⁻¹, and 0.99 g lactic acid per gram of glucose, respectively, compared to 82.7 g L⁻¹, 3.31 g L⁻¹, 1.7 g L⁻¹ h⁻¹, and 0.92 g lactic acid per gram of glucose in batch culture. This feeding method was simple and easily operated and could be feasible for industrial lactic acid production in the future.     

Kinetic and Stoichiometric Parameters in the Production of Carotenoids by <Emphasis Type="Italic">Sporidiobolus salmonicolor</Emphasis> (CBS 2636) in Synthetic and Agroindustrial Media

With the objective of determining the kinetic behavior (growth, substrate, pH, and carotenoid production) and obtain the stoichiometric parameters of the fermentative process by Sporidiobolus salmonicolor in synthetic and agroindustrial media, fermentations were carried out in shaken flasks at 25°C, 180 rpm, and initial pH of 4.0 for 120 h in the dark, sampling every 6 h. The maximum concentrations of total carotenoids in synthetic (913 μg/L) and agroindustrial (502 μg/L) media were attained approximately 100 h after the start of the fermentative process. Carotenoid bioproduction is associated with cell growth and the ratio between carotenoid production and cell growth (Y _P/X) is 176 and 163 μg/g in the synthetic and agroindustrial media, respectively. The pH of the agroindustrial fermentation medium varied from 4.2 to 8.5 during the fermentation. The specific growth rate (μ _X) for S. salmonicolor in synthetic and agroindustrial media was 0.07 and 0.04 h⁻¹, respectively. The synthetic medium allowed for greater productivity, obtaining maximum cell productivity (P _x) of 0.08 g L⁻¹ h⁻¹ and maximum total carotenoid productivity (P _car) of 14.2 μg L⁻¹ h⁻¹. Knowledge of the kinetics of a fermentative process is of extreme importance when transposing a laboratory experiment to an industrial scale, as well as making a quantitative comparison between different culture conditions.     

Variable Volume Fed-Batch Fermentation for Nisin Production by <Emphasis Type="Italic">Lactococcus lactis</Emphasis> subsp<Emphasis Type="Italic">. lactis W28</Emphasis>

A feeding technology that was suitable for improving the nisin production by Lactococcus lactis subsp. lactis W28 was established. The effects of initial sucrose concentration (ISC) in the fermentation broth, feeding time, and feeding rate on the fermentation were studied. It was observed that a fed-batch culture (ISC = 10 g l⁻¹) with 100 ml sucrose solution (190 g l⁻¹) being evenly fed (9–10 ml h⁻¹) into the fermenter after 3-h fermentation gave the best performance in terms of biomass and nisin yield. Under these conditions, the total biomass and the total nisin yield were approximately 23% and 51% higher than those in batch fermentation, respectively. When the sucrose concentration was controlled at 5–10 g l⁻¹ in variable volume intermittent fed-batch fermentation (VVIF) with ISC = 10 g l⁻¹, the total biomass and the total nisin yield were 29% and 60% above those in batch fermentation, respectively. The VVIF proved to be effective to eliminate the substrate inhibition by maintaining sucrose at appropriate levels. It is also easy to be scaled up, since various parameters involved in industrial production were taken into account.     

Evaluation of Cashew Apple Juice for the Production of Fuel Ethanol

A commercial strain of Saccharomyces cerevisiae was used for the production of ethanol by fermentation of cashew apple juice. Growth kinetics and ethanol productivity were calculated for batch fermentation with different initial sugar (glucose + fructose) concentrations. Maximal ethanol, cell, and glycerol concentrations were obtained when 103.1 g L⁻¹ of initial sugar concentration was used. Cell yield (Y _X/S) was calculated as 0.24 (g microorganism)/(g glucose + fructose) using cashew apple juice medium with 41.3 g L⁻¹ of initial sugar concentration. Glucose was exhausted first, followed by fructose. Furthermore, the initial concentration of sugars did not influence ethanol selectivity. These results indicate that cashew apple juice is a suitable substrate for yeast growth and ethanol production.     

PVA-Hydrogel Entrapped <Emphasis Type="Italic">Candida Guilliermondii</Emphasis> for Xylitol Production from Sugarcane Hemicellulose Hydrolysate

Viable cells of Candida guilliermondii were immobilized by inclusion into polyvinyl alcohol (PVA) hydrogel using the freezing–thawing method. Entrapment experiments were planned according to a 2³ full factorial design, using the PVA concentration (80, 100, and 120 g L⁻¹), the freezing temperature (−10, −15, and −20 °C), and the number of freezing-thawing cycles (one, three, and five) as the independent variables, integrated with three additional tests to estimate the errors. The effectiveness of the immobilization procedure was checked in Erlenmeyer flasks as the pellet capability to catalyze the xylose-to-xylitol bioconversion of a medium based on sugarcane bagasse hemicellulosic hydrolysate. To this purpose, the yield of xylitol on consumed xylose, xylitol volumetric productivity, and cell retention yield were selected as the response variables. Cell pellets were then used to perform the same bioconversion in a stirred tank reactor operated at 400 rpm, 30 °C, and 1.04 vvm air flowrate. At the end of fermentation, a maximum xylitol concentration of 28.7 g L⁻¹, a xylitol yield on consumed xylose of 0.49 g g⁻¹ and a xylitol volumetric productivity of 0.24 g L⁻¹ h⁻¹ were obtained.     

The pH Shift and Precursor Feeding Strategy in a Low-Toxicity FR-008/Candicidin Derivative CS103 Fermentation Bioprocess by a Mutant of <Emphasis Type="Italic">Streptomyces</Emphasis> sp. FR-008

CS103, the novel derivative of polyene macrolides antibiotic FR-008/candicidin with lower toxicity has been isolated from the culture mycelia of the mutant of Streptomyces sp. FR-008, with targeted deletions of the fscP cytochrome P450 gene from its chromosome. To enhance biosynthesis of CS103, pH shift and precursor feeding strategy for fermentation process by the mutant of Streptomyces sp. FR-008 in a stirred tank bioreactor was developed. According to the process parameters analysis, the effectiveness of the strategy was examined and confirmed by experiments. A maximal CS103 concentration of 139.98 μg/mL was obtained, 2.05-fold higher than that in the pH-uncontrolled fermentation. Compared to other three cases as pH-uncontrolled, pH-controlled, and two-stage pH-controlled batch cultures, the proposed “pH shift and precursor feeding strategy” effectively avoided the scarcity of the antibiotic precursor, increased the CS103 yield from biomass (Y _P/X) and substrate (Y _P/S) by 110.61% and 48.52%, respectively, and at the time the fermentation time was shortened from 120 to 96 h. The highest CS103 production rate (1.46 μg mL⁻¹ h⁻¹) of the pH shift and precursor feeding strategy was 284.21%, 97.30%, and 58.70% higher than that of pH-uncontrolled, pH-controlled, and two-stage pH-controlled batch culture cases, respectively.     

Fermentation Performance and Structure Characteristics of Xanthan Produced by <Emphasis Type="Italic">Xanthomonas campestris</Emphasis> with a Glucose/Xylose Mixture

The ability of Xanthomonas campestris to convert glucose and xylose to xanthan and the structure of xanthan derived from the glucose/xylose mixture media are important when the lignocelluloses hydrolysate was used in xanthan production. In this paper, the features related to xanthan fermentation in the glucose/xylose mixture media and the structures of xanthan derived from the mixture media were studied. Glucose was the preferred carbon source to produce xanthan while xylose was also utilized with a very low consumption rate. When the fraction of glucose decreased from 100% to 25%, the glucose consumption rate and xanthan production rate reduced from 0.44 g L⁻¹ h⁻¹ to 0.25 g L⁻¹ h⁻¹ and 0.21 g L⁻¹ h⁻¹ to 0.04 g L⁻¹ h⁻¹ respectively while xylose was consumed at a very stable rate (0.053–0.060 g L⁻¹ h⁻¹). On the other hand, when the xylose fraction increased from 0% to 50%, pyruvate and acetate content of xanthan increased from 2.43% to 3.78% and 2.55% to 7.05%. The existence of xylose also led to higher average molecular weight. Therefore, it could be concluded that xylose was not efficiently utilized by X. campestris to produce xanthan. The concentration of glucose rather than the total sugar was the main factor to determine the xanthan production. But xylose was helpful to improve the quality of xanthan.     

The Fed-Batch Production of a Thermophilic 2-Deoxyribose-5-Phosphate Aldolase (DERA) in <Emphasis Type="Italic">Escherichia coli</Emphasis> by Exponential Feeding Strategy Control

2-Deoxyribose-5-phosphate aldolase (DERA) catalyzes a sequential aldol reaction useful in synthetic chemistry. In this work, the effect of a feeding strategy on the production of a thermophilic DERA was investigated in fed-batch cultures of recombinant Escherichia coli BL21 (pET303-DERA008). The predetermined specific growth rate (μ _set) was evaluated at 0.20, 0.15, and 0.10 h⁻¹, respectively. The DERA concentration and volumetric productivity were associated with μ _set. The cells synthesized the enzyme most efficiently at μ _set = 0.15 h⁻¹. The maximum enzyme concentration (5.12 g/L) and total volumetric productivity (0.256 g L⁻¹ h⁻¹) obtained were over 10 and five times higher than that from traditional batch cultures. Furthermore, the acetate concentration remained at a relatively low level, less than 0.4 g/L, under this condition which would not inhibit cell growth and target protein expression. Thus, a specific growth rate control strategy has been successfully applied to induce fed-batch cultures for the maximal production of the thermophilic 2-deoxyribose-5-phosphate aldolase.     

Scale up and Application of Biosurfactant from <Emphasis Type="Italic">Bacillus subtilis</Emphasis> in Enhanced Oil Recovery

There is a lack of fundamental knowledge about the scale up of biosurfactant production. In order to develop suitable technology of commercialization, carrying out tests in shake flasks and bioreactors was essential. A reactor with integrated foam collector was designed for biosurfactant production using Bacillus subtilis isolated from agricultural soil. The yield of biosurfactant on biomass (Y _p/x), biosurfactant on sucrose (Y _p/s), and the volumetric production rate (Y) for shake flask were obtained about 0.45 g g⁻¹, 0.18 g g⁻¹, and 0.03 g l⁻¹ h⁻¹, respectively. The best condition for bioreactor was 300 rpm and 1.5 vvm, giving Y _x/s, Y _p/x, Y _p/s, and Y of 0.42 g g⁻¹, 0.595 g g⁻¹, 0.25 g g⁻¹, and 0.057 g l⁻¹ h⁻¹, respectively. The biosurfactant maximum production, 2.5 g l⁻¹, was reached in 44 h of growth, which was 28% better than the shake flask. The obtained volumetric oxygen transfer coefficient (K _L a) values at optimum conditions in the shake flask and the bioreactor were found to be around 0.01 and 0.0117 s⁻¹, respectively. Comparison of K _L a values at optimum conditions shows that biosurfactant production scaling up from shake flask to bioreactor can be done with K _L a as scale up criterion very accurately. Nearly 8% of original oil in place was recovered using this biosurfactant after water flooding in the sand pack.     

Overproduction of Glucoamylase by a Deregulated Mutant of a Thermophilic Mould <Emphasis Type="Italic">Thermomucor indicae-seudaticae</Emphasis>

Thermomucor indicae-seudaticae, a glucoamylase-producing thermophilic mould, was mutagenised using nitrous acid and gamma (⁶⁰Co) irradiation in a sequential manner to isolate deregulated mutants for enhanced production of glucoamylase. The mutants were isolated on Emerson YpSs agar containing a non-metabolisable glucose analogue 2-deoxy-d-glucose (2-DG) for selection. The preliminary screening for glucoamylase production using starch–iodine plate assay followed by quantitative confirmation in submerged fermentation permitted the isolation of several variants showing varying levels of derepression and glucoamylase secretion. The mutant strain T. indicae-seudaticae CR19 was able to grow in the presence of 0.5 g l⁻¹ 2-DG and produced 1.8-fold higher glucoamylase. As with the parent strain, glucoamylase production by T. indicae-seudaticae CR19 in 250-ml Erlenmeyer flasks attained a peak in 48 h of fermentation, showing higher glucoamylase productivity (0.67 U ml⁻¹ h⁻¹) than the former (0.375 U ml⁻¹ h⁻¹). A large-scale cultivation in 5-l laboratory bioreactor confirmed similar fermentation profiles, though the glucoamylase production peak was attained within 36 h attributable to the better control of process parameters. Although the mutant grew slightly slow in the presence of 2-DG and exhibited less sporulation, it showed faster growth on normal Emerson medium with a higher specific growth rate (0.138 h⁻¹) compared to the parent strain (0.123 h⁻¹). The glucoamylase produced by both strains was optimally active at 60 °C and pH 7.0 and displayed broad substrate specificity by cleaving α-1,4- and α-1,6-glycosidic linkages in starch, amylopectin, amylose and pullulan. Improved productivity and higher specific growth rate make T. indicae-seudaticae CR19 a useful strain for glucoamylase production.     

<Emphasis Type="Italic">Rhizopus stolonifer</Emphasis> LAU 07: a novel source of fructosyltransferase

Increasing awareness of the importance of fructooligosaccharides (FOS) as ingredients of functional foods has led to intensive search of new sources of fructosyltransferases (FTase), enzymes responsible for the conversion of sucrose to fructooligosaccharides. A local strain of Rhizopus stolonifer isolated from spoilt orange fruit with high fructosyltransferase activity (U _t) of 12.31–45.70 U mL⁻¹ during a fermentation period of 24–120 h is herein reported. It showed low hydrolytic activity (U _h) in the range of 0.86–1.78 U mL⁻¹ during the same period. FOS yield of 34 % (1-kestose, GF₂, nystose, GF₃) was produced by FTase obtained from a 72 h-old culture using 60 g of sucrose per 100 mL of the substrate. When the isolate was grown in a defined submerged medium, its pH dropped sharply from the intial value of 5.5 to 1.0 within 24 h, and this value was maintained throughout the fermentation. The biomass content ranged from 8.8 g L⁻¹ at 24 h of fermentation to reach the maximum of 10 g L⁻¹ at 72 h. It was reduced to 5.6 g L⁻¹ at the end of 120 h of fermentation. This report represents the first reference to a strain of Rhizopus as a source of FTase for the production of FOS. The high U _t/U _h ratio shown by this isolate indicates that it may be a good strain for the industrial and commercial production of FOS. However, there is a need of further optimization of the bioprocess to increase the conversion efficiency of sucrose to FOS by the enzyme.     

Ethanol Production from Cashew Apple Bagasse: Improvement of Enzymatic Hydrolysis by Microwave-Assisted Alkali Pretreatment

In this work, the potential of microwave-assisted alkali pretreatment in order to improve the rupture of the recalcitrant structures of the cashew able bagasse (CAB), lignocellulosic by-product in Brazil with no commercial value, is obtained from cashew apple process to juice production, was studied. First, biomass composition of CAB was determined, and the percentage of glucan and lignin was 20.54 ± 0.70% and 33.80 ± 1.30%, respectively. CAB content in terms of cellulose, hemicelluloses, and lignin, 19.21 ± 0.35%, 12.05 ± 0.37%, and 38.11 ± 0.08%, respectively, was also determined. Results showed that, after enzymatic hydrolysis, alkali concentration exerted influence on glucose formation, after pretreatment with 0.2 and 1.0 mo L⁻¹ of NaOH (372 ± 12 and 355 ± 37 mg g_glucan⁻¹) when 2% (w/v) of cashew apple bagasse pretreated by microwave-assisted alkali pretreatment (CAB-M) was used. On the other hand, pretreatment time (15–30 min) and microwave power (600–900 W) exerted no significant effect on hydrolysis. On enzymatic hydrolysis step, improvement on solid percentage (16% w/v) and enzyme load (30 FPU g_CAB-M⁻¹) increased glucose concentration to 15 g L⁻¹. The fermentation of the hydrolyzate by Saccharomyces cerevesiae resulted in ethanol concentration and productivity of 5.6 g L⁻¹ and 1.41 g L⁻¹ h⁻¹, respectively.     

Analysis of Carbon Metabolism and Improvement of γ-Polyglutamic Acid Production from <Emphasis Type="Italic">Bacillus subtilis</Emphasis> NX-2

Bacillus subtilis NX-2 produces γ-polyglutamic acid (γ-PGA) when using glucose and l-glutamate as carbon sources. The conversion of carbon sources into γ-PGA was analyzed with the ¹³C-NMR method after enriching the media with ¹³C-labeled glucose. The results showed that the percentage of γ-PGA monomers derived from glucose was relatively low, approximately 6% and 9%, respectively, with an initial glucose concentration of 30 and 40 g L⁻¹. It was concluded that glucose was utilized mainly as the growth-limiting substrate for cell growth and supplied the required energy during γ-PGA biosynthesis, while l-glutamate was preferred as the main substrate for γ-PGA formation. To achieve an efficient conversion of l-glutamate and enhance the γ-PGA production, a fed-batch culture was proposed by feeding of glucose. By this method, supplied l-glutamate (40 g L⁻¹) was completely depleted, and γ-PGA yield was attained 42 g L⁻¹.     

Compactin Production Studies Using <Emphasis Type="Italic">Penicillium brevicompactum</Emphasis> Under Solid-State Fermentation Conditions

In the present study, compactin production by Penicillium brevicompactum WA 2315 was optimized using solid-state fermentation. The initial one factor at a time approach resulted in improved compactin production of 905 μg gds⁻¹ compared to initial 450 μg gds⁻¹. Subsequently, nutritional, physiological, and biological parameters were screened using fractional factorial and Box–Behnken design. The fractional factorial design studied inoculum age, inoculum volume, pH, NaCl, NH₄NO₃, MgSO₄, and KH₂PO₄. All parameters were found to be significant except pH and KH₂PO₄. The Box–Behnken design studied inoculum volume, inoculum age, glycerol, and NH₄NO₃ at three different levels. Inoculum volume (p = 0.0013) and glycerol (p = 0.0001) were significant factors with greater effect on response. The interaction effects were not significant. The validation study using model-defined conditions resulted in an improved yield of 1,250 μg gds⁻¹ compactin. Further improvement in yield was obtained using fed batch mode of carbon supplementation. The feeding of glycerol (20% v/v) on day 3 resulted in further improved compactin yield of 1,406 μg gds⁻¹. The present study demonstrates that agro-industrial residues can be successfully used for compactin production, and statistical experiment designs provide an easy tool to improve the process conditions for secondary metabolite production.     

Production of Lipids Containing High Levels of Docosahexaenoic Acid by a Newly Isolated Microalga, <Emphasis Type="Italic">Aurantiochytrium</Emphasis> sp. KRS101

In the present study, a novel oleaginous Thraustochytrid containing a high content of docosahexaenoic acid (DHA) was isolated from a mangrove ecosystem in Malaysia. The strain identified as an Aurantiochytrium sp. by 18S rRNA sequencing and named KRS101 used various carbon and nitrogen sources, indicating metabolic versatility. Optimal culture conditions, thus maximizing cell growth, and high levels of lipid and DHA production, were attained using glucose (60 g l⁻¹) as carbon source, corn steep solid (10 g l⁻¹) as nitrogen source, and sea salt (15 g l⁻¹). The highest biomass, lipid, and DHA production of KRS101 upon fed-batch fermentation were 50.2 g l⁻¹ (16.7 g l⁻¹ day⁻¹), 21.8 g l⁻¹ (44% DCW), and 8.8 g l⁻¹ (40% TFA), respectively. Similar values were obtained when a cheap substrate like molasses, rather than glucose, was used as the carbon source (DCW of 52.44 g l⁻¹, lipid and DHA levels of 20.2 and 8.83 g l⁻¹, respectively), indicating that production of microbial oils containing high levels of DHA can be produced economically when the novel strain is used.     

The group-theoretical structure of the atomic g shell: connection with the alternating group <Emphasis Type="Italic">A</Emphasis><Subscript>6</Subscript> as <Emphasis Type="Italic">L</Emphasis><Subscript>2</Subscript>(9)

The special projective linear groups PSL(2ℓ + 1) or L ₂(2ℓ + 1) of order 2ℓ(2ℓ + 1)(ℓ + 1) can be used to study atomic shells of electrons with angular momentum quantum number ℓ corresponding to the atomic p, d, f, and g shells for ℓ = 1, 2, 3, 4, respectively. For the atomic g shell the group L ₂(9) is isomorphic with the alternating group A ₆ on six objects of order 360 or the symmetry group of the 5-dimensional simplex, a 5-dimensional analogue of the tetrahedron with 6 vertices and 15 edges. This leads to the subgroup chain SO(9) ⊃ SO(5) ⊃ L ₂(9) for the atomic g shell analogous to the subgroup chain SO(7) ⊃ G ₂ ⊃ L ₂(7) ≈⁷ O for the atomic f shell. In the L ₂(9) group only the representations of spherical harmonics or sums thereof, Γ(Y_ℓ), with dimensions dim Γ(Y_ℓ) or dim Γ(Y_ℓ) ± 1 divisible by 9 are found to be individually reducible to irreducible representations (irreps) or sums of irreps of L ₂(9). This leads to term groupings such as S, PD, G, PF, DH, L, PK, DI, FH, M, FI, PO, DN, HK, R, etc., of increasing total dimension for the irreps of SO(9) for various g ⁿ configurations in the atomic g shell.     

Enhancing the production of gamma-linolenic acid in <Emphasis Type="Italic">Hansenula polymorpha</Emphasis> by fed-batch fermentation using response surface methodology

Gamma-linolenic acid (GLA, C18:3Δ^6,9,12) is an n-6 polyunsaturated fatty acid (PUFA) that has been used for the alleviation and treatment of a number of symptoms and diseases. Increasing GLA demand has led to a search for alternative producers and potential strategies for GLA production. Based on the successful performance of Hansenula polymorpha, a methylotrophic yeast, as a “cell factory” for the production of valuable bioproducts, a bioprocess development approach was implemented for GLA production in the recombinant yeast carrying the mutated Δ⁶-desaturase gene of Mucor rouxii. Using a substrate-feeding strategy under glycerol-limited conditions, the physical-chemical variables during the fed-batch fermentation of the recombinant H. polymorpha were optimised for GLA production through response surface methodology using a Box-Behnken design. The medium composition, including yeast extract and trace elements, and dissolved oxygen tension (DOT) were targeted. We found that DOT was the most effective variable for enhancing GLA yield. These results also suggest that the optimum conditions for GLA production are 28 % saturation of DOT, 1 g L⁻¹ of yeast extract and 3.6 mL L⁻¹ of the Pichia trace metals 1 (PTM1).     

Microbial Production of Propionic Acid with <Emphasis Type="Italic">Propionibacterium freudenreichii</Emphasis> Using an Anion Exchanger-Based In Situ Product Recovery (ISPR) Process with Direct and Indirect Contact of Cells

The recovery of an inhibiting product from a bioreactor soon after its formation is an important issue in industrial bioprocess development. In the present study, the potential of the anion exchanger-based in situ product recovery (ISPR) technique for the biocatalytic production of propionic acid was discussed. The focus of the current work was the selection of a suitable configuration of metabolically active cells for application in propionic acid production. Accumulation of propionic acid in fermentation broth caused feedback inhibition of the growth and biotransformation activity of Propionibacterium freudenreichii CICC 10019. Relevant product inhibition kinetics was discussed, and the results showed that keeping the aqueous propionic acid concentration below 10.02 g L⁻¹ was an essential prerequisite for ISPR process. A batch study, in which three ISPR configuration mode designs were compared, was conducted. The comparison indicated that employing an external direct mode had significant advantages over other modes in terms of increased productivity and product yield, with a corresponding decrease in the number of downstream processing steps, as well as in substrate consumption. The fed-batch culture using an external direct mode for the continuous accumulation of propionic acid resulted in a cumulative propionic acid concentration of 62.5 g L⁻¹, with a corresponding product yield of 0.78 g propionic acid/g glucose.     

Simultaneous production of citric acid and erythritol from crude glycerol by Yarrowia lipolytica Wratislavia K1

This study shows a possible microbial process for utilization of crude glycerol generated by the biodiesel industry for citric acid and erythritol production. Simultaneous production of citric acid and erythritol under nitrogen-limited conditions with glycerol as the carbon source was achieved with an acetate negative mutant of Y. lipolytica Wratislavia K1 in fed-batch cultivations. The effect of the initial glycerol concentration (from 30–180 g dm⁻³) on the citrate and erythritol production was investigated. As a result of the experiments, maximum citric acid production (110 g dm⁻³) and a very high amount of erythritol (81 g dm⁻³) were determined after 168 h of fed-batch cultivation with the initial glycerol concentration of 150 g dm⁻³ and the total glycerol concentration of 250 g dm⁻³. In addition, the citric acid to isocitric acid ratio of the products from this strain was 35.5:1. Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May 2007.