Initial Sucrose Concentration Research Articles

Biohydrogen production from beet molasses by sequential dark and photofermentation

Biological hydrogen production using renewable resources is a promising possibility to generate hydrogen in a sustainable way. In this study, a sequential dark and photofermentation has been employed for biohydrogen production using sugar beet molasses as a feedstock. An extreme thermophile Caldicellulosiruptor saccharolyticus was used for the dark fermentation, and several photosynthetic bacteria ( Rhodobacter capsulatus wild type, R. capsulatus hup − mutant, and Rhodopseudomonas palustris) were used for the photofermentation. C. saccharolyticus was grown in a pH-controlled bioreactor, in batch mode, on molasses with an initial sucrose concentration of 15 g/L. The influence of additions of NH 4 + and yeast extract on sucrose consumption and hydrogen production was determined. The highest hydrogen yield (4.2 mol of H 2/mol sucrose) and maximum volumetric productivity (7.1 mmol H 2/L c.h) were obtained in the absence of NH 4 +. The effluent of the dark fermentation containing no NH 4 + was fed to a photobioreactor, and hydrogen production was monitored under continuous illumination, in batch mode. Productivity and yield were improved by dilution of the dark fermentor effluent (DFE) and the additions of buffer, iron-citrate and sodium molybdate. The highest hydrogen yield (58% of the theoretical hydrogen yield of the consumed organic acids) and productivity (1.37 mmol H 2/L c.h) were attained using the hup − mutant of R. capsulatus. The overall hydrogen yield from sucrose increased from the maximum of 4.2 mol H 2/mol sucrose in dark fermentation to 13.7 mol H 2/mol sucrose (corresponding to 57% of the theoretical yield of 24 mol of H 2/mole of sucrose) by sequential dark and photofermentation.

Application of a model using the phenomenological approach for prediction of growth and xanthan gum production with sugar cane broth in a batch process

Production of xanthan gum was studied and modelled using unstructured kinetic models composed of three differential equations, which considered the microbial biomass, carbon source, and xanthan concentration. The fermentation process, using Xanthomonas campestris pv. campestris NRRL B-1459, was conducted under controlled conditions with diluted sugar cane broth at different initial sucrose concentrations (15.0, 25.0, and 35.0 g L −1). Unstructured kinetic models proposed in the literature for this system were reviewed and applied. These models were tested against the experimental results, calculating the parameters by nonlinear regression. The kinetic models used in this study provided estimations of microbial growth, substrate consumption, and product formation, and, therefore, these parameters were quantified in the fermentation experiments. Higher yield of xanthan per amount of sucrose (0.58 g g −1) and productivity (0.63 g L −1 h −1) were obtained using initial sucrose concentrations of 25.0 and 35.0 g L −1, respectively. The models were used to predict the kinetic parameters for a medium containing an intermediate and a larger initial sucrose concentration (27.0 and 40.0 g L −1). When tested experimentally, the measured fermentation parameters were in close agreement with the values predicted by the model that presented the best adjustment, demonstrating its validity.

Optimization of C:N ratio and minimal initial carbon source for poly(3‐hydroxybutyrate) production by Bacillus megaterium

AbstractBACKGROUND: The aim of this research was the optimization of poly(3‐hydroxybutyrate)—P(3HB)—production in submerged cultures of Bacillus megaterium in a mineral medium using sucrose as carbon source and nitrogen as the limiting substrate. Small‐scale experiments were carried out in shake flasks at 30 °C and 160 rpm in order to evaluate the best initial sucrose concentration and carbon:nitrogen ratio to maximize biomass accumulation and biopolymer production. An objective function in terms of residual sucrose and P(3HB) production was proposed in order to optimize the amount of carbon source used and the production of P(3HB).RESULTS: High production of P(3HB) was obtained, with approximately 70% (CDW) accumulation in cells without nitrogen limitation and strongly correlated with the pH of the culture. Scaling‐up the system to cultures in a bioreactor, with or without pH control, a reduction of P(3HB) accumulation (around 30% CDW) was observed when compared with shaker cultures, suggesting a possible role of oxygen limitation as a stress signaling for P(3HB) synthesis.CONCLUSIONS: Results of our experiments showed that Bacillus megaterium was able to produce P(3HB) at one of the highest production rates so far reported for this bacterium, making this microorganism very interesting for industrial applications. Comparisons of shaker and bench‐scale bioreactor experiments show both the importance of pH and aeration strategies. It is likely that complex aeration strategies linked to cell metabolism will be necessary for further developments using this bacterium. Copyright © 2009 Society of Chemical Industry

Hydrolysis of sucrose using sulfonated poly(vinyl alcohol) as catalyst

The hydrolysis of sucrose was carried out over poly(vinyl alcohol) (PVA) with sulfonic acid groups, at 80 °C. The products of sucrose hydrolysis were glucose and fructose. A series of PVA with different crosslinking degree were prepared. It was observed that the catalytic activity of PVA matrix increases with the crosslinking degree, due to the increases of the amount of sulfonic acid groups on PVA. Further, the influence of various reaction parameters, such as, catalyst loading, initial concentration of sucrose and temperature, on the hydrolysis of sucrose over PVA_40 was studied. It was found that at 80 °C, with 0.511 g of catalyst loading and with an initial concentration of sucrose of 0.6 M, a sucrose conversion of about 90%, after 3 h, could be obtained. The PVA_40 catalyst was recycled and reused with negligible loss in the activity. A simple kinetic model was developed assuming that the sucrose hydrolysis is an irreversible reaction and the first order with respect to the sucrose concentration. Since the concentration profiles of the reactant and the products do not exhibit any pronounced initial inductive period, the external and internal diffusion of the reactant and products on the catalyst were not considered. It was observed that the kinetic model fits experimental concentration data quite well.

Induction and Repression Kinetics of Fungal Beta-Fructofuranosidase in Submerged Culture

Invertase production by Aspergillus niger in submerged culture was evaluated under different concentrations of sucrose and glucose. When the initial concentration of sucrose was increased from 6.25 to 50 gL-1, a higher biomass production (6.1 gL-1) was observed. The biomass production was increased 4 times more when a glucose-sucrose combination was used as substrate (26.31 gL-1). The strain A. niger produced extracellular beta-fructofuranosidase activity at all test concentrations of the substrate and the highest enzymatic activity (3873 UL-1) was obtained when sucrose was used at 12.5 gL-1. However, with a glucose-sucrose concentration of 25 gL-1 the beta-fructofuranosidase activity was of 23706 UL-1. The maximum rate of invertase enzyme production in presence of sucrose by Aspergillus niger in submerged culture was 3.67 UL-1h-1 at 12.5 gL-1 concentration, while in the case of glucose-sucrose mixture, it was 13.95 UL-1h-1 at a concentration of 25 gL-1. It was observed that the enzyme yield (YE/X) was 1.25 times more in presence of sucrose than with glucose-sucrose combination. In addition, the results suggested that an addition of lower concentration of glucose is a viable option to increase the enzyme secretion by the fungi.

Predictive expressions of growth and Remazol Turquoise Blue-G reactive dye bioaccumulation properties of Candida utilis

The combined effects of initial sucrose and initial Remazol Turquoise Blue-G (RTBG) reactive dye concentrations on the specific growth rate and dye bioaccumulation efficiency of Candida utilis was investigated and optimized using response surface methodology (RSM) in this study. A 2 2 full factorial central composite design was successfully used for experimental design and analyses of the results. Two numerical correlations fitted to a second-order quadratic equation were obtained to estimate the responses of specific growth rate and dye uptake yield. The statistical analysis indicated that both the microbial growth and removal yield of dye enhanced with raising sucrose concentration up to 15 g l −1 and diminished with the increase in initial RTBG dye concentration up to approximately 500 mg l −1 due to inhibition caused by high concentrations of RTBG dye. The optimum combination predicted via RSM confirmed that C. utilis was capable of bioaccumulating RTBG with the maximum uptake yield of 82.0% in 15 g l −1 sucrose and 50 mg l −1 dye containing growth medium.

김치로부터 분리된 Leuconostoc sp. strain YSK 균주에 의한 덱스트란 생산 조건의 최적화

본 연구는 발효 김치 액으로부터 덱스트란 생산 균주를 분리하고 생산 최적 생산 조건을 정하기 위하여 반응표면 분석법을 이용하였다. 발효 조건의 독립변수들은 배양 온도,pH, 효모 추출물의 농도, 온도, 기질의 농도로 정하고 Box- Benken 디자인를 이용하여 실험을 설계하였다. 최종 분리된 균주는 Leuconostoc sp. strain SKY로 잠정적으로 명하였다. 연구 결과 덱스트란 생산은 3.90 - 22.40 g/l이고, 균체량 생산은 0.69-2.85 g/l, 수율은 0.10-0.64, 생산 속도 0.16-0.85 g/l-hr의 범위에서 분석이 되었다. 표면반응분석 결과 덱스트란 생산에 가장 영향을 미치는 것은 배양 pH이고 다음에 효모 추출물의 농도 그리고 온도의 순으로 나타났다. 균체량 생산에 가장 영향을 미치는 것은 배양 pH이고 다음에 효모 추출물의 농도 그리고 온도의 순으로 나타났다. 생산 수율에 가장 영향을 미치는 것은 배양 pH 이고 다음에 효모 추출물의 농도 그리고 온도의 순으로 나타났다. 덱스트란 생산 속도에 가장 영향을 미치는 것은 배양 pH이고 다음에 효모 추출물의 농도 그리고 온도의 순으로 나타났다. 결론적으로 최적 생산 조건은 온도는 <TEX>$27-28^{\circ}C$</TEX>이고, pH는 7.0이며, 효묘 추출물은 6-7%의 범위에서 결정이 되었다. 이러한 조건에서 생산된 덱스트란 양은 22g/l이고, 생산 수율은 약 60%정도이며, 생산 속도는 0.8g/l/hr이었다. A bacterium producing non- or partially digestible dextran was isolated from kimchi broth by enrichment culture technique. The bacterium was identified tentatively as Leuconostoc sp. strain SKY. We established the response surface methodology (Box-Behnken design) to optimize the principle parameters such as culture pH, temperature, and yeast extract concentration for maximizing production of dextran. The ranges of parameters were determined based on prior screening works done at our laboratory and accordingly chosen as 5.5, 6.5, and 7.5 for pH, 25, 30, and <TEX>$35^{\circ}C$</TEX> for temperature, and 1, 5, and 9 g/l yeast extract. Initial concentration of sucrose was 100 g/l. The mineral medium consisted of 3.0 g <TEX>$KH_2PO_4$</TEX>, 0.01 g <TEX>$FeSO_4{\cdot}H_2O$</TEX>, 0.01 g <TEX>$MnSO_4{\cdot}4H_2O$</TEX>, 0.2 g <TEX>$MgSO_4{\cdot}7H_2O$</TEX>, 0.01 g NaCl, and 0.05 g <TEX>$CaCO_3$</TEX> per 1 liter deionized water. The optimum values of pH and temperature, and yeast extract concentration were obtained at pH (around 7.0), temperature (27 to <TEX>$28^{\circ}C$</TEX>), and yeast extract (6 to 7 g/l). The best dextran yield was 60% (dextran/g sucrose). The best dextran productivity was 0.8 g/h-l.

Influence of Auxins and Sucrose in Monoterpenoid Oxindole Alkaloid Production by Uncaria tomentosa Cell Suspension Cultures

Growth and alkaloid production in Uncaria tomentosa cell suspension cultures were studied in Murashige and Skoog medium supplemented with 10 microM 2,4-dichlorophenoxyacetic acid, 10 microM kinetin, and 58 mM sucrose for maintenance and with 10 microM indole-3-acetic acid, 10 microM kinetin, and 58 mM sucrose for production. A U. tomentosa pale Uth-3 cell line, cultured in the production medium, showed a reduced lag phase and a specific growth rate (mu) of 0.27 day(-1), while cells growing in the maintenance medium showed mu = 0.20 day(-1). U. tomentosa cells growing in the production medium produced monoterpenoid oxindole alkaloids (MOA) in amounts of 10.2 +/- 1.6 microg g(-1) dry weight (DW). The chemical profile of MOA produced by in vitro cell cultures was similar to that found in the plant. After 10 subcultures, maximum MOA production decreased to 2.0 +/- 0.7 microg g(-1) DW, while tryptamine alkaloids (TA) were produced with a maximum of 6.2 +/- 0.4 microg g(-1) DW. The increase of initial sucrose concentration up to 145 mM in the production medium enhanced the cell biomass by 3.2-fold (from 10.2 +/- 0.1 to 32.8 +/- 1.1 g DW L(-1)), reduced mu from 0.27 to 0.23 day(-1), and provoked a substantial accumulation of TA (23.1 +/- 4.7 microg g(-1) DW). A high sucrose concentration stimulated MOA production in the maintenance medium (2.7 +/- 0.5 microg g(-1) DW), even in the presence of 2,4-dichlorophenoxyacetic acid.

Variable Volume Fed-Batch Fermentation for Nisin Production by Lactococcus lactis subsp. lactis W28

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.

Sucrose Biotransformation to Fructooligosaccharides by Aspergillus sp. N74 Free Cells

Fructooligosaccharide production with the fructosyltransferase from free cells of the native strain Aspergillus sp. N74 at laboratory level was evaluated. The biomass of the native strain Aspergillus sp. N74 was produced in a sucrose fermentation medium and was employed in the enzymatic reaction in solutions of sucrose and phosphate buffer, where pH, temperature, and initial sucrose concentration effect were evaluated. Fructooligosaccharides and reaction subproducts were identified and quantified by high-performance liquid chromatography. The enzyme produced by the strain Aspergillus sp. N74 possessed hydrolytic and transfructosylating activities that changed with process conditions. The best transfructosylating condition was obtained at 80 min reaction time at pH 5.5, 60 °C, and initial sucrose concentrations higher than 550 g L−1, with fructooligosaccharide production of about 50% w/w (based on initial sucrose concentration) and conversion selectivity higher than 90%. In addition, the transfructosylating and hydrolytic activities ratio was of 20. The high transfructosylating activity showed by the fructosyltransferase produced from the native strain Aspergillus sp. N74 suggest considering it as an alternative for the scale-up production of fructooligosaccharides by means of the whole microorganism at bench and pilot plant levels.

Ultrasonic properties of partially frozen sucrose solutions

Ultrasonic velocity and attenuation were measured as a function of temperature (−10 °C to 0 °C) in partially frozen sucrose solutions (25%, 30%, 35%, 40%, 50% by wt) which had either been degassed under vacuum or not prior to freezing. Ultrasonic velocity increased approximately linearly with ice content in all cases and was somewhat affected by the initial sucrose concentration and degassing. The high ultrasonic attenuation in frozen systems was determined mainly by the presence of air bubbles and only weakly by ice content.

Simultaneous production of 2,3-butanediol, ethanol and hydrogen with a Klebsiella sp. strain isolated from sewage sludge

A Klebsiella sp. HE1 strain isolated from hydrogen-producing sewage sludge was examined for its ability to produce H 2 and other valuable soluble metabolites (e.g., ethanol and 2,3-butanediol) from sucrose-based medium. The effect of pH and carbon substrate concentration on the production of soluble and gaseous products was investigated. The major soluble metabolite produced from Klebsiella sp. HE1 was 2,3-butanediol, accounting for over 42–58% of soluble microbial products (SMP) and its production efficiency enhanced after increasing the initial culture pH to 7.3 (without pH control). The HE1 strain also produced ethanol (contributing to 29–42% of total SMP) and a small amount of lactic acid and acetic acid. The gaseous products consisted of H 2 (25–36%) and CO 2 (64–75%). The optimal cumulative hydrogen production (2.7 l) and hydrogen yield (0.92 mol H 2 mol sucrose −1) were obtained at an initial sucrose concentration of 30 g COD l −1 (i.e., 26.7 g l −1), which also led to the highest production rate for H 2 (3.26 mmol h −1 l −1), ethanol (6.75 mmol h −1 l −1) and 2,3-butanediol (7.14 mmol h −1 l −1). The highest yield for H 2, ethanol and 2,3-butanediol was 0.92, 0.81 and 0.59 mol mol-sucrose −1, respectively. As for the overall energy production performance, the highest energy generation rate was 27.7 kJ h −1 l −1 and the best energy yield was 2.45 kJ mol sucrose −1, which was obtained at a sucrose concentration of 30 and 20 g COD l −1, respectively.

Fructooligosaccharides production by Aspergillus sp. N74 in a mechanically agitated airlift reactor

Batch fructooligosaccharides (FOSs) production by fructosyltransferase from Aspergillus sp. N74 in a mechanically agitated airlift reactor was investigated. Two biomass concentrations (6 and 9.5 g L −1 in biomass dry weight) of Aspergillus sp. N74 were used for the evaluation of fructosyltransferase activity. The enzymatic reactions were carried out at the following conditions: initial sucrose concentration 70% (w/v), pH 5.5, 60 °C, 350 rpm, and superficial aeration rate 0.012 m s −1; the reactor was operated in batch for 26 h. A biomass concentration and time reaction effect on FOS production and composition was observed. The obtained FOS yield ( Y FOS) for 6 g L −1 of biomass dry weight was 69% (43% 1-kestose and 26% nystose), while for 9.5 g L −1 of biomass dry weight a peak in the Y FOS of 70% was observed (43% 1-kestose, 25% nystose and 2% 1-β-fructorianosyl nystose) after 4 h of reaction, which was reduced to the 57% (18% 1-kestose, 33% nystose and 6% 1-β-fructofuranosyl nystose) at the end of the reaction time. These results present the designed reactor and the native strain Aspergillus sp. N74 as an industrial alternative for the fructooligosaccharides production.

Enhanced hyaluronic acid production by a two-stage culture strategy based on the modeling of batch and fed-batch cultivation of Streptococcus zooepidemicus

This study aimed to enhance hyaluronic acid (HA) production by a two-stage culture strategy based on the modeling of batch and fed-batch culture of Streptococcus zooepidemicus. Batch culture had higher specific HA synthesis rate while fed-batch culture had higher specific cell growth rate. The lower specific HA synthesis rate in fed-batch culture resulted from the competition of cell growth for the common precursors at a low substrate concentration. Based on the modeling of batch and fed-batch culture of S. zooepidemicus, a two-stage culture strategy was proposed to enhance HA production. S. zooepidemicus were cultured in a fed-batch mode with sucrose concentration maintained at 1.0 ± 0.2 g/L during 0–8 h and then batch culture was performed during 8–20 h with an initial sucrose concentration of 15 g/L. With the proposed two-stage culture strategy, HA production was increased to 6.6 g/L compared with 5.0 g/L in batch culture with the same total sucrose. The enhanced HA production by the proposed two-stage culture strategy resulted from the decreased inhibition of cell growth and the increased transformation rate of sucrose to HA.

Significance of inoculation density and carbon source on the mycelial growth and Tuber polysaccharides production by submerged fermentation of Chinese truffle Tuber sinense

Truffles are among the most valuable gourmet mushrooms on the market. By taking Chinese truffle Tuber sinense as a typical example, a submerged fermentation process for the production of mycelia and Tuber polysaccharides was developed for the first time. Significances of inoculation density, carbon source and its initial concentration were studied in details. For inoculation density within the range of 160–653 mg dry weight (DW)/L, a maximal biomass of 15.59 ± 0.59 g DW/L was obtained at its lowest level of 160 mg DW/L, while the maximal extracellular polysaccharides (EPSs) production of 1.97 ± 0.08 g/L was attained at its highest level of 653 mg DW/L. The maximal intracellular polysaccharides (IPSs) production of 1.40 ± 0.10 g/L was obtained at its level of 487 mg DW/L. The carbon sources examined were glucose, maltose, sucrose and lactose, and sucrose was suitable for the cell growth and IPS production. Lactose was beneficial for EPS production although the cell could not grow well. There was no β-galactosidase activity when T. sinense grew in lactose, which was the reason why lactose was not favorable for the cell growth. Initial sucrose concentration within the range of 20–125 g/L significantly affected the process. At sucrose 125 g/L, both biomass (i.e., 24.07 ± 1.94 g/L) and EPS production (i.e., 2.85 ± 0.04 g/L) reached their peak values. The maximal IPS production of 2.92 ± 0.20 g/L was obtained at sucrose 80 g/L. This work demonstrated the submerged fermentation of Chinese truffle T. sinense is a potential alternative for the efficient production of mycelia and Tuber polysaccharides.

One-step synthesis of isomalto-oligosaccharide syrups and dextrans of controlled size using engineered dextransucrase

Isomalto-oligosaccharides and dextrans of controlled molecular weight of about 10 and 40 kDa were produced using a simple one-step process using engineered L. mesenteroides NRRL B-512F dextransucrase variants. Isomalto-oligosaccharides were produced in a 58% yield by the acceptor reaction with glucose, and reached a degree of polymerization of at least 27 glucosyl units. Reaction conditions for optimal synthesis of dextrans of controlled molecular weight were defined, in respect of initial sucrose concentration and reaction temperature. Thus, we achieved synthesis with impressive yields of 69 and 75% for the 40 and 10 kDa dextran species, respectively. These two dextran sizes are particularly suitable for clinical applications, and are of great industrial demand. Compared with the traditional processes based on chemical hydrolysis and fractionation, which achieve only low yields, the new enzymatic methods offer improvement in quantity, quality and efficiency.

Use of response surface methodology (RSM) in the evaluation of growth and copper(II) bioaccumulation properties of Candida utilis in molasses medium

The influential factors on simultaneous growth and copper(II) bioaccumulation by growing cells of Candida utilis yeast under various ambient conditions, such as changing concentrations of molasses sucrose and copper(II) were tested. The highest growth rate of 0.133 h −1 was obtained at an initial sucrose concentration of 15 g l −1 in absence of copper(II). For each constant sucrose concentration chosen between 5 and 15 g l −1, the increase in initial copper(II) concentration up to 500 mg l −1 resulted in a decrease in the percentage uptake of copper(II) and moreover all copper(II) concentrations tested inhibited the yeast growth. On the other hand, at each constant copper(II) concentration studied, both the growth and copper(II) uptake yield enhanced with raising sucrose concentration up to 15 g l −1. Maximum uptake yield of 34.2% was observed in 15 g l −1 sucrose and 50 mg l −1 copper(II) containing growth medium. The binary effects of initial sucrose and copper(II) concentrations on the specific growth rate and copper(II) uptake yield of yeast were analyzed by experimental design method and two model equations for predicting the growth rate and copper(II) uptake yield of yeast due to arbitrarily chosen sucrose and copper(II) concentrations were developed by using response surface methodology (RSM).

Biomass production ofAnoectochilus formosanus hayata in a bioreactor system

We investigated the factors that affect biomass production fromAnoectochilus formosanus in a bioreactor system. Those factors included inoculum size, initial sucrose concentration, media supplements, photosynthetic photon flux density (PPFD), and cuIturing methods. An inoculum size of 8 g L−1 was most suitable for shoot proliferation; biomass accumulation was optimized when the medium was supplemented with 3% sucrose compared with sucrose-free media or those containing concentrations of 6% or 9%. This accumulation also was enhanced under a PPFD of 50 μmol m2 s−1. Likewise, the addition of coconut water (50 mL L−1) plus activated charcoal (0.5 mg L−1) to our Hyponex medium proved most beneficial. Comparative studies among three bioreactor systems — continuous immersion, raft (net), and temporary immersion (the ebb and flood system) — revealed that shoot proliferation and biomass accumulation were more efficient when culturing was performed under continuous immersion.

Enhancement of phenylethanoid glycosides biosynthesis in cell cultures of Cistanche deserticola by osmotic stress

The effect of osmotic stress on cell growth and phenylethanoid glycosides (PeGs) biosynthesis was investigated in cell suspension cultures of Cistanche deserticola Y. C. Ma, a desert medicinal plant grown in west region of China. Various initial sucrose concentrations significantly affected cell growth and PeGs biosynthesis in the suspension cultures, and the highest dry weight and PeGs accumulation reached 15.9 g l(-1)-DW and 20.7 mg g(-1)-DW respectively at the initial osmotic stress of 300 mOsm kg(-1) where the sucrose concentration was 175.3 mM. Stoichiometric analysis with different combinations of sucrose and non-metabolic sugar (mannitol) or non-sugar osmotic agents (PEG and NaCl) revealed that osmotic stress itself was an important factor for enhancing PeGs biosynthesis in cell suspension cultures of C. deserticola. The maximum PeGs contents of 26.9 and 23.8 mg g(-1)-DW were obtained after 21 days at the combinations of 87.6 mM sucrose with 164.7 mM mannitol (303 mOsm kg(-1)) or 20 mM PEG respectively, which was higher than that of C. deserticola cell cultures grown under an initial sucrose concentration of 175.3 mM after 30 days. The stimulated PeGs accumulation in the cell suspension cultures was correlated to the increase of phenylalanine ammonium lyase (PAL) activity induced by osmotic stress.

Application of fractional factorial design to levan production by Zymomonas mobilis

Levan is a non-toxic, biologically active, extra cellular polysaccharide composed solely by fructose units. Optimization of levan production by Zymomonas mobilis strain ZAG-12 employing a 24-1 fractional factorial design was performed to analyze the influence of the temperature (20, 25 e 30oC) agitation (50, 75 e 100 rpm), and the initial concentrations of both sucrose (150, 200 e 250 g.L-1) and yeast extract (2.0, 3.5 e 5.0g.L-1) on final levan concentration. Aerobic fermentation was performed batchwise in 500mL Pyrex flasks for 72 hours. Biomass, ethanol, levan and sucrose were determined at beginning and also at end of the fermentations. The experiments showed that the final levan concentration depended on initial sucrose concentration, temperature and agitation velocity and that the initial concentration of yeast extract did not influence levan production. However, when the production of ethanol and biomass were considered, it became evident that yeast extract was a significant variable. The best conditions for levan production occurred at 100 rpm agitation, 20oC and 250g.L-1 of initial sucrose resulting in 14.67g.L-1 of levan.