Stirred Tank Fermentor Research Articles

Phellinus baumii으로부터 세포외 다당체 생산의 최적화

장수상황버섯(Phellinus baumii)의 균사체 성장 및 세포외 다당체(exopolysaccharides) 생산을 위한 액체배양의 최적 배지 및 배양조건에 관한 실험을 수행한 결과, 최적배양 온도와 초기 pH는 각각 3<TEX>$0^{\circ}C$</TEX>와 5.0으로 결정되었다. 탄소원의 경우, cellobiose와 maltose가 균사체 성장에는 양호하였으나 저조한 세포외 다당체 생산을 보였으며, 반면에 fructose 와 mannitol 은 상대적으로 높은 수율의 세포외 다당체 생산과 균사체 성장 또한 양호하였다. 최적 질소원으로는 yeast extract가 균사체 성장뿐만 아니라 세포외 다당체 생산에 효과적인 것으로 결정되었다. 최적 배지의 조성은 fructose 20 g/L, yeast extract 20 g/L 및 <TEX>$CaCl_2$</TEX> 0.55 g/L이었으며, 최적 배양조건 하에서 5-L 교반 발효조를 운전한 결과, 최대 균사체 성장(17.43 g/L)과 최대 세포외 다당체 생산(3.6 g/L)을 얻을 수 있었다. 회수된 세포외 다당체는 glycoprotein이었으며 그 조성은 amino acid분석 결과 주로 arginine (14.1%)과 glycin (12.0%)이었으며, cabohydrate의 경우는 mannose (48.7%)와 arabinose (38.4%)이 주성분이었다. The polysaccharide isolated from Phellinus species has been known as a folk remedy, including antitumor and immune-stimulating activities. However, there are lacks of knowledge about mycelial growth and exopolysaccharide (EH) production in its submerged culture. We investigated the optimal conditions on mycelial growth and EPS production in Phellinus baumii. The optimal temperature and initial pH for mycelial growth and EPS production in shake flask culture of P. baumii were proved to be 3<TEX>$0^{\circ}C$</TEX> and pH 5.0, respectively. In case of carbon source, cellobiose and maltose were highly efficient for mycelial growth and fructose and mannitol were also relatively favorable for EPS production. Yeast extract was the most suitable nitrogen source for mycelial growth and EPS production. The composition of optimal culture medium was determined to be fructose 20 g/L, yeast extract 20 g/L, and <TEX>$CaCl_2$</TEX> 0.55 g/L, respectively. Under the optimal culture condition, the maximum mycelial biomass and EPS achieved in a 5-L stirred-tank fermenter were 17.43 g/L and 3.6 g/L, respectively. It was found that the EPS was a glycoprotein onsisted of mainly arginine (14.1%) and glycine (12.0 %) in protein moiety and mainly mannose (48.7%) and arabinose (38.4%) in carbohydrate moiety.

Utilization of mathematical models to investigate the bifurcation and chaotic behavior of ethanol fermentors

This paper uses an experimentally verified model to explore the conditions for increasing productivity and yield of the ethanol fermentation process. Detailed bifurcation analysis is carried out to uncover the rich static and dynamic behavior of the fermentor with/without ethanol removal membranes. The emphasis is on producing higher ethanol yield and productivity through unconventional modes of operation. Possible increase of sugar conversion and ethanol productivity using periodic and chaotic operation at high sugar concentrations is investigated for continuous stirred tank fermentors with/without ethanol removal membranes. This study is the prelude to an extensive experimental program to investigate the chaotic behavior of an experimental fermentor with/without ethanol selective membrane leading to scaling up the experimental fermentor to an industrial sized fermentor.

Production of heterologous protein by Methylobacterium extorquens in high cell density fermentation

The green fluorescent protein (GFP) was used as a model protein to study the recombinant protein production by the strain Methylobacterium extorquens ATCC 55366. Scale-up from shake flasks to 20 l fed-batch fermentation was achieved using methanol as a sole carbon and energy source and a completely minimal culture medium. Two different expression vectors were used to express GFP. Clone PCM-GFP containing the vector pCM110 with native promoter of the methanol dehydrogenase P mxaF produced approximately 100-fold more GFP than the clone PRK-GFP containing the vector pRK310 with the heterogeneous promoter P lac . Several fed-batch fermentations with and without selective pressure (tetracycline) were run in a 20 l stirred tank fermenter using the two different clones of M. extorquens. The methanol concentration was monitored with an on-line semiconductor gas sensor in the culture broth. It was maintained at a non-toxic level of 1.4 g l −1 with an adaptative control which regulates the methanol feed rate. The same growth profile was achieved in all fermentations. The maximum growth rate ( μ max) was 0.18 h −1 with an overall yield ( Y X/ S ) of 0.3 g g −1 methanol. With this high cell density fermentation process, we obtained high levels (up to 4 g l −1) of GFP with the clone PCM-GFP. The maximum specific GFP production ( Y GFP/ X ) with this clone was 80 mg g −1 representing approximately 16% of the total cell protein. Additional feeding of pure oxygen to the fermenter permitted a longer phase of exponential growth but had no effect on the total yields of biomass and GFP. The specific GFP production of clone PCM-GFP remained unaffected in the presence or absence of selective pressure (tetracycline), within the initial 50 h of the fermentation culture. These results suggest that M. extorquens ATCC 55366 could be an interesting candidate for overexpression of recombinant proteins.

Production of β-Carotene From Beet Molasses by Blakeslea trispora in Stirred-Tank and Bubble Column Reactors: Development of a Mathematical Modeling

The effect of aeration rate and agitation speed on beta-carotene production from molasses by Blakeslea trispora in a stirred-tank fermentor and optimization of the production of the pigment in a bubble column reactor were investigated. In addition, a central composite design was employed to determine the maximum beta-carotene concentration at optimum values for the process variables (aeration rate, sugar concentration, linoleic acid, kerosene). By image analysis of the morphology of the fungus, a quantitative characterization of the hyphae and zygospores formed was obtained. The hyphae were differentiated to intact hyphae, vacuolated hyphae, evacuated cells and degenerated hyphae. An increased proportion of zygospores was correlated to high beta-carotene production. In the stirred-tank fermentor, the highest concentration of the carotenoid pigment (92.0 mg/L) was obtained at an aeration rate of 1.5 vvm and agitation speed of 60 rpm. In the bubble column reactor, the aeration rate and concentration of sugars, linoleic acid, kerosene, and antioxidant significantly affected the production of beta-carotene. In all cases, the fit of the model was found to be good. Aeration rate, sugar concentration, linoleic acid, and kerosene had a strong positive linear effect on beta-carotene concentration. Moreover, the concentration of the pigment was significantly influenced by the negative quadratic effects of the given variables and by their positive or negative interactions. Maximum beta-carotene concentration (360.2 mg/L) was obtained in culture grown in molasses solution containing 5% (w/v) sugar supplemented with linoleic acid (37.59 g/L), kerosene (39.11 g/L), and antioxidant (1.0 g/L).

Stability of beta-carotene in spray dried preparation of Rhodotorula glutinis mutant 32.

To obtain beta-carotene-rich dry cell preparation from mutant 32 of Rhodotorula glutinis and determination of its pigment stability. The mutant 32 of R. glutinis was grown in a 14 l stirred tank fermenter. Cell mass was concentrated 10-fold by cross-flow microfiltration and then spray dried. Butylated hydroxy toluene (BHT) and d-tocopherol were used as protecting agents. A two-level, three-variable, factorial optimization was performed to achieve moisture-free, non-viable and beta-carotene-rich feed additive. The beta-carotene and cell mass in stirred tank fermenter were found to be 54 +/- 5 mg l-1 and 12.8 +/- 2 g l-1, respectively. In the presence of BHT, 97 +/- 3% (w/w) beta-carotene was recovered for all the inlet temperatures studied. The best beta-carotene and yeast powder recoveries were obtained at 160 degrees C, 11.6% (w/v) cell mass concentration and 1 g l-1 BHT. The pigments inside dried yeast powder were stable in dark and cold condition for at least 10 weeks. The purified beta-carotene got almost totally denatured, under similar conditions of storage, within 76 h. Spray dried and stable preparation of beta-carotene-rich yeast, R. glutinis can provide alternative source of beta-carotene for use in animal nutrition.

Effect of pH on the production and molecular weight distribution of exopolysaccharide by Antrodia camphorata in batch cultures

The effects of culture pH ranging from pH 3.0 to 6.0 on cell growth, exopolysaccharide biosynthesis and molecular weight distribution of exopolysaccharides of Antrodia camphorata were examined both in shake flask culture and in a stirred tank fermenter. In a controlled pH stirred tank fermentation, the optimum pH for cell growth was 4.0 with a cell yield at 0.3 g/g while that for exopolysaccharide formation was 5.0 with a product yield at 5.05 mg/g. A relatively high molecular weight exopolysaccharide with a lower yield was obtained at low pH values while a relatively low molecular weight exopolysaccharide with a high yield was obtained at higher pH values. The average molecular weight of the exopolysaccharide in the flask culture was higher than that in the stirred tank fermenter. A two stage pH process that maximized product formation was demonstrated with a high product yield of 148 mg/l with the relatively high average molecular weight of 2.18×10 5.

Production and characterization of exopolysaccharides from submerged culture of Phellinus linteus KCTC 6190

The optimal temperature and initial pH for both mycelial growth and exopolysaccharide (EPS) production in shake flask cultures of Phellinus linteus KCTC 6190 were found to be 30 °C and pH 4.0, respectively. Optimal medium composition was determined to be sucrose 50 g/l, corn steep powder 3 g/l, KH 2PO 4 0.68 g/l, and CaCl 2 0.55 g/l. Under optimal culture conditions, the maximum mycelial biomass and EPS achieved in a 5-l stirred-tank fermenter indicated 11 and 3.3 g/l, respectively. To the best of our knowledge, this is the highest polysaccharide yield amongst liquid cultures of P. linteus reported in the literature. The three groups of EPSs (designated as Fr-I, -II, and -III) were obtained from the culture filtrates by a gel filtration chromatography on Sepharose CL-4B and the different fractions were analyzed directly using the size exclusion chromatography coupled with multi-angle laser-light scattering (SEC/MALLS) analysis. It was revealed that all fractions of EPS were polysaccharides consisted of mainly mannose, galactose, and glucose. The molecular weights of Fr-I, -II, and -III of EPS were determined to be 433,400 (±7801), 31,470 (±283), and 12,950 (±90) g/mol, respectively. The SEC/MALLS analysis revealed that molecular dimension of the Fr-I was a spherical form, whereas the Fr-II was a random coil in an aqueous solution.

Approaches to stabilization of inter-domain recombination in polyketide synthase gene expression plasmids.

Regions of extremely high sequence identity are recurrent in modular polyketide synthase (PKS) genes. Such sequences are potentially detrimental to the stability of PKS expression plasmids used in the combinatorial biosynthesis of polyketide metabolites. We present two different solutions for circumventing intra-plasmid recombination within the megalomicin PKS genes in Streptomyces coelicolor. In one example, a synthetic gene was used in which the codon usage was reengineered without affecting the primary amino acid sequence. The other approach utilized a heterologous subunit complementation strategy to replace one of the problematic regions. Both methods resulted in PKS complexes capable of 6-deoxyerythronolide B analogue biosynthesis in S. coelicolor CH999, permitting reproducible scale-up to at least 5-l stirred-tank fermentation and a comparison of diketide precursor incorporation efficiencies between the erythromycin and megalomicin PKSs.

An age-structured population balance model for microbial dynamics

This work presents an age-structured population balance model (ASPBM) for a bioprocess in a continuous stirred-tank fermentor. It relates the macroscopic properties and dynamic behavior of biomass to the operational parameters and microscopic properties of cells. Population dynamics is governed by two time- and age-dependent density functions for living and dead cells, accounting for the influence of substrate and dissolved oxygen concentrations on cell division, aging and death processes. The ASPBM described biomass and substrate oscillations in aerobic continuous cultures as experimentally observed. It is noteworthy that a small data set consisting of nonsegregated measurements was sufficient to adjust a complex segregated mathematical model.

Exploration and exploitation of bifurcation/chaotic behavior of a continuous fermentor for the production of ethanol

A four-dimensional model for the anaerobic fermentation process, developed and used earlier to simulate the oscillatory behavior of an experimental continuous stirred tank fermentor is utilized in the present investigation to explore the static/dynamic bifurcation and chaotic behavior of this fermentor, which is shown to be quite rich. The present investigation is a prelude to the experimental exploration of bifurcation and chaos in a membrane fermentor. Dynamic bifurcation (periodic attractors) as well as period doubling sequences leading to different types of periodic and chaotic attractors have been uncovered. It is fundamentally and practically important to discover the fact that in some cases, periodic and chaotic attractors have higher ethanol yield and production rate than the corresponding steady states.

Production of pullulan using an oscillatory baffled bioreactor

AbstractPullulan is a well‐known extracellular polysaccharide produced by the aerobically growing yeast‐like fungus Aureobasidium pullulans (A pullulans). Pullulan has a wide range of commercial and industrial applications, eg it is used in adhesives, in laminates or nylon‐like fibres and fabrics, and in various foods as a low calorie ingredient. Pullulan itself is produced and deposited on the outside of the fungal cells, and because of the low oxygen permeability of the pullulan, this layer acts as a barrier for the transfer of oxygen from the medium to the fungus. This could be detrimental to the survival of the cells and, in turn, restrict the cultivation of the pullulan. In pullulan fermentation it is therefore desirable to break up and remove this layer of pullulan adherent to the cells. The conventional impeller‐driven vessels often exhibit a gradient in mixing capabilities, with high intensities at and near the impeller but low intensities in peripheral regions. Such gradients increase significantly with the scale. The existence of the mixing gradient in a given vessel can potentially inhibit the process of pullulan generation in regions distant from the impeller, leading to reduced productivity. The oscillatory baffled bioreactor (OBB) offers enhanced and uniform mixing at very low shear rate compared with conventional mixing vessels; this would provide better control over the cultivation of pullulan. In this paper, the production of pullulan in the OBB is reported and compared with the fermentation process carried out in a conventional stirred tank fermenter.© 2003 Society of Chemical Industry

Formula omitted]-lactic acid production by pellet-form Rhizopus oryzae R1021 in a stirred tank fermentor

L(+) -lactic acid and its salts are being widely used in food and pharmaceutical industries. Rhizopus oryzae is known to be outstanding in producing optically pure L(+)-lactic acid. Rhizopus cultures are morphologically complex. They can grow as extended filamentous form, mycelial mats, mycelial pellets or clumps. Different morphology growth forms can have a significant effect on the rheology of the fermentation broth that will affect the performance of the bioreactor. The factors that affect the morphology and L(+) -lactic acid productivity of R. oryzae R1021 were investigated in detail in this work. Studies on the relationship among CaCO 3 addition, inoculum size, concentration of NH 4NO 3, agitation speed, aeration rate and the morphology of the mycelial growth and lactic acid production were carried out. Uniform sized mycelial pellet growth (diameter of 1.0– 2.0 mm ) was obtained when the time of adding CaCO 3 is 8 h after fermentation. The pellet form exhibited a higher lactic acid yield than clump form. An inoculated spore concentration of 10 6 spores/ml induced uniform pellet in preculture medium, and then formed the small mycelial pellets in production medium and a maximum L(+) -lactic acid concentration of 72.62 g/l was observed at the inoculum level of 3×10 6 spores/ml . Further studies on the effect of agitation speed on the fungal morphology showed that increasing agitation speed caused the fungal pellets to decrease in size but to increase in number per unit volume. Similar studies on the effect of aeration rate on the fungal morphology showed that increasing aeration rate caused the fungal pellets to increase in size but to decrease in number per unit volume. When agitation speed and aeration rate were 300 r/ min and 0.6 vvm , the final L(+) -lactic acid concentration and the biomass concentration are 76.1 and 9.62 g/l , respectively, after 36 h culture of R. oryzae R1021 in pellet form (average pellet size, 1.4 mm ) in stirred tank fermentor with initial glucose concentration of 100 g/l . L(+) -lactic acid production and the yield of L(+) -lactic acid based on the initial glucose are above 74.92 g/l and 74.2%, respectively, in 6 batches repetitive fermentation.

Optimization of submerged culture process for the production of mycelial biomass and exo-polysaccharides by Cordyceps militaris C738.

The objective of the present study was to determine the optimal culture conditions for mycelial biomass and exo-polysaccharide (EPS) by Cordyceps militaris C738 in submerged culture. The optimal temperatures for mycelial biomass and EPS production were 20 degrees C and 25 degrees C, respectively, and corresponding optimal initial pHs were found to be 9 and 6, respectively. The suggested medium composition for EPS production was as follows: 6% (w/v) sucrose, 1% (w/v) polypeptone, and 0.05% (w/v) K2HPO4. The influence of pH on the fermentation broth rheology, morphology and EPS production of C. militaris C738 was carried out in a 5-l stirred-tank fermenter. The morphological properties were comparatively characterized by pellet roughness and compactness by use of image analyser between the culture conditions with and without pH control. The roughness and compactness of the pellets indicated higher values at pH-stat culture (pH 6.0), suggesting that larger and more compact pellets were desirable for polysaccharide production (0.91 g g(-1) cell d(-1). Under the optimized culture conditions (with pH control at 6), the maximum concentration of biomass and EPS were 12.7 g l(-1) and 7.3 g l(-1), respectively, in a 5-l stirred-tank fermenter. The critical effect of pH on fungal morphology and rheology presented in this study can be widely applied to other mushroom fermentation processes.

Influence of nutritional conditions on the mycelial growth and exopolysaccharide production in Paecilomyces sinclairii.

The objective of the study was to optimize the submerged culture conditions for the production of exopolysaccharide from Paecilomyces sinclairii. The optimal temperature and initial pH for exopolysaccharide production by Paecilomyces sinclairii in shake flask culture were found to be 30 degrees C and 6.0, respectively. Sucrose (60 g l(-1)) and corn steep powder (10 g l(-1)) were the most suitable carbon and nitrogen source for exopolysaccharide production. Under optimal culture medium, the maximum exopolysaccharide concentration in a 5-l stirred-tank fermenter indicated 7.4 g l(-1), which was approximately three times higher than that in basal medium. The maximum specific growth rates (micro max) and yield coefficient (Y(P/S)) in the optimal culture medium was 0.16 h(-1) and 0.19, respectively. The optimal culture conditions reported in this article can be widely applied to the processes for submerged cultures of other mushrooms.

Characterization of pullulan produced from beet molasses by Aureobasidium pullulans in a stirred tank reactor under varying agitation

The molecular characteristics of pullulan produced from beet molasses, following their pretreatment with sulfuric acid and activated carbon, by Aureobasidium pullulans P56 (a melanin-deficient strain) in a stirred tank fermentor under varying agitation conditions have been examined. A maximum pullulan concentration of 49 g l −1, biomass dry weight of 25 g l −1, pullulan yield of 50% and sugar utilization of 97% were achieved at an initial sugar concentration in the medium of 100 g l −1 and impeller speed of 700 rpm; under these conditions the pO 2 levels in the bioreactor were maintained at low levels of dissolved O 2 saturation (∼7%). Structural characterization of the isolated polysaccharides from the fermentation broths by 13 C NMR spectroscopy and pullulanase digestion combined with size exclusion chromatography confirmed the identity of pullulan and the homogeneity (>94% d.b.) of the elaborated polysaccharides by the microorganism. The exopolysaccharide preparations were also free of contaminating proteins. Using multiangle laser light scattering (MALLS) and refractive index (RI) detectors, in conjunction with high-performance size-exclusion chromatography (HPSEC), molecular size distributions and estimates of the molecular weight ( M w=5.3–14.7×10 4), root-mean square of the radius of gyration ( R g=24–33 nm) and polydispersity index ( M w/ M n=1.7–2.6) were obtained. In most culture systems examined there was a reduction in the molecular size of the isolated polysaccharides as time of fermentation progressed. In the concentration range of 2.8–9.5% (w/v), the solution rheological behavior of the isolated pullulans was almost Newtonian (within 1 and 1200 s −1 at 20 °C). Overall, beet molasses were proven as an attractive fermentation medium for the production of pullulan by A. pullulans.

Production of carboxylic acids from hydrolyzed corn meal by immobilized cell fermentation in a fibrous-bed bioreactor

Corn meal hydrolyzed with amylases was used as the carbon source for producing acetic, propionic, and butyric acids via anaerobic fermentations. In this study, corn meal, containing 75% (w/w) starch, 20% (w/w) fibers, and 1.5% (w/w) protein, was first hydrolyzed using amylases at 60 °C. The hydrolysis yielded approximately 100% recovery of starch converted to glucose and 17.9% recovery of protein. The resulting corn meal hydrolyzate was then used, after sterilization, for fermentation studies. A co-culture of Lactococcus lactis and Clostridium formicoaceticum was used to produce acetic acid from glucose. Propionibacterium acidipropionici was used for propionic acid fermentation, and Clostridium tyrobutylicum was used for butyric acid production. These cells were immobilized on a spirally wound fibrous matrix packed in a fibrous-bed bioreactor (FBB) developed for multi-phase biological reactions or fermentation. The bioreactor was connected to a stirred-tank fermentor that provided pH and temperature controls via medium circulation. The fermentation system was operated at the recycle batch mode. Temperature and pH were controlled at 37 °C and 7.6, respectively, for acetic acid fermentation, 32 °C and 6.0, respectively, for propionic acid fermentation, and 37 °C and 6.0, respectively, for butyric acid production. The fermentation demonstrated a yield of approximately 100% and a volumetric productivity of approximately 1 g/(l h) for acetic acid production. The propionic acid fermentation achieved an approximately 60% yield and a productivity of 2.12 g/(l h), whereas the butyric acid fermentation obtained an approximately 50% yield and a productivity of 6.78 g/(l h). These results were comparable to, or better than those fermentations using chemically defined media containing glucose as the substrate, suggesting that these carboxylic acids can be efficiently produced from direct fermentation of corn meal hydrolyzate. The corn fiber present as suspended solids in the corn meal hydrolyzate did not cause operating problem to the immobilized cell bioreactor as is usually encountered by conventional immobilized cell bioreactor systems. It is concluded that the FBB technology is suitable for producing value-added biochemicals directly from agricultural residues or commodities such as corn meal.

Importance of carbon source feeding and pH control strategies for maximum kojic acid production from sago starch by Aspergillus flavus

To maximize kojic acid production by Aspergillus flavus Link 44-1 using gelatinized sago starch as a carbon source, the performance of different fermentation modes (batch and fed-batch with different feeding modes) was investigated in an 8- l stirred tank fermentor. The addition of a large volume of concentrated sago starch (140 g/ l) 2 d after the start with an initial starch concentration of 60 g/ l produced the maximum concentration of kojic acid (16.43 g/ l), which was about 4 times higher than that for batch fermentation of 100 g/ l sago starch. Further improvement of kojic acid production was obtained by adding small amounts of concentrated starch (140 g/ l) intermittently at 2-d intervals to the culture. Using this technique of fermentation, the dissolved oxygen tension (DOT) can be controlled at high levels (40–50% saturation) during the active growth phase, which is required for the enhanced secretion of α-amylase used for saccharification of starch and also for the production of mycelia with higher ability in synthesizing kojic acid. Maintaining the culture pH at 3 throughout the intermittent fed-batch fermentation reduced kojic acid production (7.26 g/ l) significantly. Very little kojic acid (0.93 g/ l) was produced when the pH was kept at 4 during the growth phase and then lowered to 3 during the production phase. A high level of kojic acid production (31.00 g/ l) was achieved in fermentation where the pH was not controlled throughout the cultivation or not controlled during the growth phase but kept at 3 during the production phase. This result indicates that the pH control strategy is important; with the variation in culture pH during the growth phase being most significant and critical to kojic acid production.

Study and Mathematical Modeling of the Production of Propionic Acid by Propionibacterium acidipropionici Immobilized in a Stirred Tank Fermentor

A mathematical model was developed that describes production of propionic acid by fermentation of sweet whey with Propionibacterium acidipropionici immobilized in calcium polygalacturonate beads in a fermentor-type stirred tank. This mathematical model is constituted by a partial differential equations system, which fits consumption, production, growth and internal diffusion rates in the support. Fermentation was experimentally studied with free cells and immobilized cells, effective diffusivities of lactose and propionic acid were estimated in the support, and typical parameters of the model were obtained by nonlinear regression of the experimental data. The variance analysis shows that the combination of micro(max) and K(d) parameters is the source of variation most significative, also they were found to be the most sensitive parameters of the model. Finally, an effectiveness factor was calculated in order to assess the effect of mass transfer on the overall reaction rate observed.

Beta-Carotene production in sugarcane molasses by a Rhodotorula glutinis mutant.

Several wild strains and mutants of Rhodotorula spp. were screened for growth, carotenoid production and the proportion of -carotene produced in sugarcane molasses. A better producer, Rhodotorula glutinis mutant 32, was optimized for carotenoid production with respect to total reducing sugar (TRS) concentration and pH. In shake flasks, when molasses was used as the sole nutrient medium with 40 g l(-1) TRS, at pH 6, the carotenoid yield was 14 mg l(-1) and -carotene accounted for 70% of the total carotenoids. In a 14-l stirred tank fermenter, a 20% increase in torulene content was observed in plain molasses medium. However, by addition of yeast extract, this effect was reversed and a 31% increase in -carotene content was observed. Dissolved oxygen (DO) stat fed-batch cultivation of mutant 32 in plain molasses medium yielded 71 and 185 mg l(-1) total carotenoids in double- and triple-strength medium, respectively. When supplemented with yeast extract, the yields were 97 and 183 mg l(-1) total carotenoid with a 30% increase in -carotene and a simultaneous 40% decrease in torulene proportion. Higher cell mass was also achieved by double- and triple-strength fed-batch fermentation.

Cultivation of Absidia coerulea for Chitosan Production in a Modified Airlift Reactor

Cultivation of Absidia coerulea for chitosan production was carried out in a modified airlift reactor with two concentric wire mesh draft tubes. The oxygen requirement for the cultivation was high and the microorganisms were sensitive to shear stress. The modified reactor which had high oxygen transfer capability provided a suitable environment for the cultivation. Production of chitosan in the modified reactor was more than two times higher than those in both the conventional bubble column and the stirred tank fermenter with impeller speed of 600 rpm and 55% higher than that in the stirred tank fermenter with the impeller speed of 300 rpm. By using the proposed reactor, the molecular weight and degree of deacetylation of chitosan at the end of 65 hr cultivation were 1050 kDa and 92.5 %, respectively, which were much higher than those using the stirred tank fermenter. The values were 710 kDa and 85.2 % for the stirred tank fermenter with impeller speed of 600 rpm; 820 kDa and 88.1 % for the stirred tank fermenter with impeller speed of 300 rpm. By using the bubble column, the molecular weight and degree of deacetylation were 950 kDa and 92.2%, respectively.