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Biochemical Engineering Journal (v.49, #1)
Aerobic biodegradation of wheat stillage (distillery wastewater) at an elevated temperature—Effect of solids separation by Małgorzata Krzywonos; Edmund Cibis; Agnieszka Ryznar-Luty; Tadeusz Miśkiewicz; Daniel Borowiak (pp. 1-6).
The aim of the study was to determine how the separation of solids affects the course and efficiency of the batch process of wheat stillage (distillery wastewater) biodegradation using meso- and thermophilic bacteria of the genus Bacillus. The processes with and without solids separation were conducted for 144h in a 5-L bioreactor, with aeration at 1.6vvm, stirrer revolutions of 550/min, at a constant pH (pH=6.5) and the temperature of 45°C. The results have shown that the separation of solids is superfluous, because it had only a minor effect on the reduction in the chemical oxygen demand determined in the substrate upon solids separation (SCOD). The extent of SCOD reduction amounted to 88.25% for non-filtered and 92.85% for filtered stillage. Moreover, during biodegradation of the non-filtered stillage the bacterial consortium was able per se to remove more than 50% of the suspended solids present in the stillage in the amount of approx. 50g/L (the biomass produced being neglected).
Keywords: Aerobic digestion; Bacillus; Distillery; Stirred-tank reactor; Waste treatment; Wheat stillage
Mathematical modelling of ethanol production by mixed kefir grains yeast population as a function of temperature variations by Katja Zajšek; Andreja Goršek (pp. 7-12).
A mathematical model was developed to describe the effect of temperature and fermentation time on the kinetic parameters of ethanol production by the mixed kefir grains yeast population, using full fat cow's milk as a fermentation medium. Modified Gompertz model was used to describe this phenomenon. The kinetic parameters of the model were successfully predicted by using the least-square method. The influence of temperature on kefir grains biomass increase and microbiological composition of kefir product and kefir grains was investigated and quantified. Furthermore, Arrhenius relationship between operating temperature and the maximum ethanol production rate was established. The activation energy of ethanol production was 64.3kJ/mol. The adopted mathematical model could describe very well the dynamics of ethanol production from the beginning up to the stationary phase during the kefir fermentation.
Keywords: Mathematical modelling; Milk fermentation; Kefir; Ethanol production; Microbial population; Activation energy
Biosynthesis and biocompatibility of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) produced by Cupriavidus necator from spent palm oil by Urmila Rao; R. Sridhar; P.K. Sehgal (pp. 13-20).
The ability of Cupriavidus necator to grow and produce poly(3-hydroxybutyrate-co-4-hydroxybutyrate), P(3HB-co-4HB), on spent palm oil left after frying activities, and 1,4-butanediol as precursors of 3HB and 4HB, respectively, was evaluated. The isolated polymer was characterized by13C NMR spectroscopy and differential scanning calorimetry. The mole fraction of 4-hydroxybutyrate units was 15mol% despite the presence of polar compounds like triglyceride trimers in the spent palm oil. The results demonstrate that inexpensive spent palm oil is an excellent carbon source for efficient production of PHA using C. necator. The isolated biopolyester was subjected to a depyrogenation procedure and either blended with vitamin E or physically immobilized on collagen and the biocompatibility of the biopolyester films were evaluated in chick chorioallantoic membrane (CAM). The biocompatibility evaluation indicates that the depyrogenated poly(3-hydroxybutyrate-co-4-hydroxybutyrate) blends have the potential to be developed as a new absorbable biomaterial for medical applications.
Keywords: Polyhydroxyalkanoates; Spent palm oil; Differential scanning calorimetry; NMR; Depyrogenation; Blends; Chick chorioallantoic membrane
The effect of pendant hydrophobicity on the biological efficacy of polyethylenimine conjugate by Ling-Yu Su; Tsuei-Yun Fang; Wen-Chi Tseng (pp. 21-27).
Modifying cationic polymers by conjugating a pendant group is a commonly used approach for improving the biological efficacy of gene delivery. Polyethylenimine (PEI) of MW 25,000, a potent cationic polymer for gene delivery, was employed as the primary carrier. Three different types of PEI conjugates were prepared by grafting cellobiose, polyethylene glycol of MW 350 (PEG), and 1-iodododecane, respectively, to assess the hydrophobic effect on the biological efficacy and chemicophysical properties of the DNA–polymer complexes. Increasing the hydrophobicity of the conjugate was found to decrease the biological efficacy including the levels of transgene expression and cellular viability. When the conjugate hydrophobicity was high enough to form micelles below 0.11mg/mL, the reduction in transgene expression became moderated but was accompanied with a sharp decrease in cellular viability. On the other hand, when the conjugate hydrophobicity was decreased by conjugating PEG or cellobiose at the optimal % of around 1.2%, the level of transgene expression was enhanced while at the same time maintaining the cellular viability and the chemicophysical properties of the complexes. These results suggested that a hydrophilic pendant group could better promote the biological efficacy of PEI by decreasing the hydrophobicity.
Keywords: Biomaterials engineering; Controlled release; Cell engineering; Biopolymers; Transfection; Non-viral vectors
Ethanol production from corn stover hemicellulosic hydrolysate using immobilized recombinant yeast cells by Jing Zhao; Liming Xia (pp. 28-32).
Ethanol production from corn stover hemicellulosic hydrolysate was investigated using immobilized recombinant Saccharomyces cerevisiae yeast cells. Detoxification of hemicellulosic hydrolysate by roto-evaporation and lime neutralization was carried out to remove volatile fermentation inhibitors. All furfural and more than 50% acetic acid in the hydrolysate were removed, meanwhile the xylose concentration was enhanced to 71.8g/L. The fermentability of the detoxified hydrolysate was significantly improved using immobilized cells of recombinant S. cerevisiae by Ca-alginate. An ethanol concentration of 31.1g/L and the corresponding ethanol yield on fermentable sugars of 0.406g/g were obtained within 72h in batch fermentation of the detoxified hydrolysate with immobilized cells. In addition, repeated batch fermentation of immobilized recombinant S. cerevisiae cells was attempted for ethanol production for 5 batches. The concentration of ethanol in each batch maintained above 30.1g/L with the ethanol yield on fermentable sugars over 0.393g/g. These results demonstrate the viability and significance of ethanol production from corn stover hemicellulosic hydrolysate.
Keywords: Corn stover; Hemicellulose; Hydrolysate; Ethanol; Recombinant yeast; Immobilized cell
Recovery of 1-butanol from aqueous solutions using zeolite ZSM-5 with a high Si/Al ratio; suitability of a column process for industrial applications by V. Saravanan; D.A. Waijers; M. Ziari; M.A. Noordermeer (pp. 33-39).
Commercially available zeolites (CBV28014, CBV901) with a high Si/Al ratio were tested as adsorbents to recover 1-butanol from aqueous solutions such as acetone–butanol–ethanol (ABE) fermentation broth. It was found that these zeolites can quickly and almost completely adsorb 1-butanol from aqueous solutions containing ∼1wt% of 1-butanol. The binding capacity of the zeolites appeared to be around 0.12g 1-butanol/g zeolite, and remained constant till equilibrium concentration as low as 0.04wt% 1-butanol in water. Extrudates were prepared and tested in a column set-up to get an impression of the suitability of these zeolites for industrial applications. Extrudates of 80% zeolite and 20% alumina binder with 16–24 mesh (0.7–1.0mm) size showed the best adsorption results in a packed bed column with up-flow of ABE broth. The adsorbent loading at 10% breakthrough was calculated to be 0.085g 1-butanol/g zeolite (9.3min residence time). A subsequent temperature swing leads to desorption. By choosing the temperature program carefully, it was possible to separate the water/ethanol/acetone and 1-butanol fractions. The resulting 1-butanol concentration in the 1-butanol fraction was 84.3wt% and thus a concentration factor of 65 was achieved in one step, which is a higher value compared to other isolation techniques. Only 80% of adsorbed 1-butanol could be recovered, the remainder could only be desorbed at higher temperatures as butene. However, this should not be a problem in an industrial process as all stronger binding, catalytic sites will be blocked after the first adsorption/desorption round. A mathematical model was developed to simulate the breakthrough data and a mass transfer coefficient ( kpa) of 0.052min−1 was obtained. Comparison of simulated kpa for different sizes of extrudates clearly indicated that the adsorption rate is determined by solid phase diffusion.
Keywords: Bio-butanol; Adsorption; ABE fermentation; ZSM-5 zeolite; Biofuel
Cleanability study of complex geometries: Interaction between B. cereus spores and the different flow eddies scales by W. Blel; P. Legentilhomme; C. Le Gentil-Lelièvre; C. Faille; J. Legrand; T. Bénézech (pp. 40-51).
Wall shear stress measurements and the distribution size of turbulent structures at the confined zone near the wall were used in order to investigate the cleanability of a part of a dairy processing line consisting in a manometer and a two-way valve. Geometry of equipment was discerned as an important factor governing the flow behavior and thereafter the initial contamination and the cleanability of the installation. Interactions between suspended spores and coherent turbulent structures of different sizes were used to explain the eventual re-adhesion of spores in confined zones of the loop. These interactions also helped to explain the role of the bursting phenomenon in the increase of the wall shear stress which induces spores detachment.
Keywords: Cleaning-in-place; Eddies scales; Hydrodynamics; Mass transfer; Microbial; Optimisation
Medium optimization for production of flavin mononucleotide by the recombinant strain of the yeast Candida famata using statistical designs by Valentyna Y. Yatsyshyn; Daria V. Fedorovych; Andriy А. Sibirny (pp. 52-60).
The recombinant strain of the yeast Candida famata 13-76 that overexpresses FMN1 gene coding for riboflavin kinase, accumulates significant amounts of flavin mononucleotide (FMN) in the cultural liquid. The effectiveness of FMN production by this strain under different conditions was evaluated. First, the medium composition was optimized in shake flask cultures. After preliminary experiments for nitrogen source selection, the two-level Plackett–Burman (PB) design was performed to screen medium components that significantly influence the FMN production. Among the 15 variables tested, KH2PO4, CaCl2, (NH4)6Mo7O24, CuSO4 and yeast extract, were identified as the most significant factors for FMN production (confidence levels above 95%). In order to investigate the quantitative effects for five variables selected from PB design on FMN production, a central composite design (CCD) was subsequently employed for further optimization. The optimization strategies used led to a 4.77-fold increase in the FMN production. A batch culture profile in a 1L fermenter was consequently designed according to the optimal medium observed in shake flasks. A final FMN concentration of 231±4.11mg/L was obtained in 40h, which further verified the practicability of the used strategy.
Keywords: Candida famata; Flavin mononucleotide production; Medium optimization; Plackett–Burman design; Central composite design; Response surface methodology
Enhancement of dihydroxyacetone production by a mutant of Gluconobacter oxydans by Lijuan Ma; Wenyu Lu; Zhendong Xia; Jianping Wen (pp. 61-67).
To improve the yield of 1,3-dihydroxyacetone (DHA) and the bioconversion rate of glycerol by Gluconobacter oxydans ( G. oxydans), He–Ne laser irradiation technology was employed in this work. Under the optimal irradiation doses of 21mW, 21min, mutant G. oxydans GM51 with high DHA production capacity and stable heredity was obtained through tolerance tests to glycerol and DHA. Activity of the key enzyme, glycerol dehydrogenase, in GM51 was 5.01U/mL after 30h culture, 75.17% higher than that in the wild (2.86U/mL) with the same initial glycerol concentration of 100g/L. The culture time of GM51 had been shortened by 16h (conventional culture time is 58h). DHA yield of GM51 was up to 91.5%, increased by 77.6% with an improvement of DHA productivity from 1.29 to 2.29gL−1h−1 when cultivated in 7L bioreactor. Moreover, comparative studies on kinetics of the mutant and wild further confirmed the decrease in inhibitory of substrate and product through He–Ne laser irradiation. The mutagenesis mechanism was speculated as the mutation of the gene encoding glycerol dehydrogenase, which led to improvement in the activity of this enzyme. Therefore, He–Ne laser irradiation could efficiently enhance the DHA production ability of G. oxydans.
Keywords: He–Ne laser irradiation; Bioconversion; 1,3-Dihydroxyacetone; Glycerol; Enzyme activity; Kinetics
Discriminated release of phenolic substances from red wine grape skins ( Vitis vinifera L.) by multicomponent enzymes treatment by Anis Arnous; Anne S. Meyer (pp. 68-77).
Detailed insight into the effects of enzymatic treatments on grape phenolics is of significant importance for grape processing for wine making. This study examined the release of phenols during enzymatic (pectinolytic and cellulolytic) degradation of the cell wall polysaccharides in skins of Merlot and Cabernet Sauvignon wine grapes ( Vitis vinifera L.). Anthocyanins were released from skins during the early phases of the enzymatic treatments, but were then degraded during further enzymatic treatment; flavonols underwent transformation from glycosylated (rutin) to deglycosylated (quercetin) during the enzymatic treatment; phenolic acids, including hydroxybenzoic acids and hydroxycinnamic acids, were released as a function of monosaccharides liberation, i.e. as a function of the enzyme catalyzed cell wall degradation of the skins, and with some of the phenolic acids perhaps released from the lignin. The data moreover suggest that p-coumaric acid was also released during enzyme catalyzed degradation of acylated anthocyanins, probably as a result of cinnamate esterase activity. The data thus provided unexpected new clues as to how the enzymatic treatment with multicomponent pectinolytic enzymes may promote (a) discriminated release of phenols from grape skins, and (b) molecular changes in the phenols.
Keywords: Phenols; Enzymatic extraction; Plants cell walls; Pectinase; Anthocyanins; Phenolic acids; Flavonols
Removal of emulsified oil from oily wastewater using agricultural waste barley straw by Shariff Ibrahim; Shaobin Wang; Ha Ming Ang (pp. 78-83).
An agricultural byproduct, barley straw, was chemically modified by a cationic surfactant, hexadecylpyridinium chloride monohydrate (CPC) and employed as an adsorbent to remove emulsified canola oil from aqueous solution. The textural and surface properties of the surfactant modified barley straw (SMBS) were characterized by N2 adsorption, FT-IR, SEM, surface acidic/basic groups and surfactant desorption. The low desorption of CPC from SMBS demonstrated a strong bonding of the CPC to straw surface. Several factors such as adsorption temperature, solution pH, loading of adsorbent, and particle size on oil adsorption were investigated. It was found that addition of CPC created a non-polar layer on barley straw surface thus endowing SMBS with much better adsorption capacity for oil removal from water. The adsorption was found less favorable at high acidic condition and the maximum adsorption capacity was observed at about neutrality. Larger particle size would result in lower adsorption while adsorption temperature would not affect oil adsorption significantly. The kinetic study revealed that equilibrium time was short and the isotherm study indicated that the oil adsorption was fitted well by the Langmuir model. The adsorption capacity determined from the Langmuir isotherm was 576.0±0.3mgg−1 at 25°C.
Keywords: Modified barley straw; Agricultural byproduct; Emulsified canola oil; Cationic surfactant
Modelling of fixed-bed adsorption of mono-, di-, and fructooligosaccharides on a cation-exchange resin by Katarína Vaňková; Pavel Ačai; Milan Polakovič (pp. 84-88).
Kinetics of fixed-bed adsorption of simple saccharides (glucose, fructose, and sucrose) and fructooligosaccharides (1-kestose, 1-nystose, and 1F-fructofuranosyl nystose) on process-size particles of cation exchanger Amberlite™ CR1320Ca was investigated. A step-up method of frontal chromatography was used when several inlet concentration steps were made in the range of 0–20gdm−3. The obtained experimental data were fitted simultaneously using the general rate model with two estimated parameters, which were the distribution coefficient of linear adsorption isotherm and solid-phase diffusion coefficient. The contribution of individual transport phenomena to dispersion of adsorption fronts was discussed.
Keywords: Bioseparations; Chromatography; Adsorption; Mass transfer; Ion-exchange; Modelling
Cytochrome c in sodium dodecyl sulfate reverse micelle nanocage: From a classic electron carrier protein to an artificial peroxidase enzyme by Farzaneh Farivar; Ali Akbar Moosavi-Movahedi; Yahya Sefidbakht; Khodadad Nazari; Jun Hong; Nader Sheibani (pp. 89-94).
Cytochrome c (Cyt c) is a hemoprotein involved in shuttling electrons in the mitochondrial electron transport chain. Under oxidative stress conditions, the interaction of Cyt c with anionic phospholipids results in significant enhancement of its peroxidase activity that is essential during apoptosis. Reverse micelles are convenient membrane mimetic nanostructures and were used here to simulate Cyt c peroxidase activity. Cyt c peroxidase activity was markedly enhanced in sodium dodecyl sulfate (SDS) reverse micelles. This was dependent on buffer concentration of water pool and mass percentage of buffer in reverse micelles. Fluorescence intensity based on tryptophan residue, electronic absorption curves, and circular dichroism measurements indicated partial unfolding and cleavage of axial methionin 80-Fe bond of Cyt c in reverse micellar medium resulting in the formation of a peroxidase-like artificial enzyme.
Keywords: Cytochrome c; SDS reverse micelles; Artificial enzyme; Nanoencapsulation; Guaiacol; AOT; Horseradish peroxidase model
Kinetics of hyaluronic acid production by Streptococcus zooepidemicus considering the effect of glucose by Mashitah Mat Don; Noor Fazliani Shoparwe (pp. 95-103).
An unstructured model of hyaluronic acid (HA) fermentation by Streptococcus zooepidemicus considering the effect of glucose was proposed and validated. Experiments were performed in a glucose concentration range of 10–60gl−1 in a 2l bioreactor of batch mode. Three different models, namely, the Logistic equations for cell growth, the Logistic incorporated Leudeking–Piret-like equation for glucose consumption, and the Logistic incorporated Leudeking–Piret equation with time delay, Δ t, for HA productions were proposed. The kinetic parameters were estimated by fitting the experimental data to the models. Simulation was made using the estimated kinetics parameter values and was compared with the experimental data. For glucose inhibition, S. zooepidemicus tolerated up to 40gl−1 glucose. Beyond this concentration, cell growth was inhibited. The Han and Levenspiel model and the Teissier-type model gave the best fit for all the systems studied with R 2 of 0.997 and 0.985, respectively.
Keywords: Hyaluronic acid; Stirred tank bioreactor; Kinetics; Mathematical models; Submerged; Biopolymer
Statistical optimization of media for mycelial growth and exo-polysaccharide production by Lentinus edodes and a kinetic model study of two growth morphologies by Yi-Li Feng; Wei-Qi Li; Xue-Qian Wu; Jun-Wen Cheng; Su-Yun Ma (pp. 104-112).
Lentinus edodes (shiitake mushroom) is a well-known medicinal and edible mushroom throughout the world. Statistical optimization was employed to optimize the culture medium for maximum mycelial growth and exo-polysaccharide (EPS) production in submerged fermentation: Plackett–Burman design (PBD) was applied to determine significant factors, followed by the paths of steepest ascent to move to the general vicinity of the optimum and Box–Behnken design (BBD) to obtain the final optimum culture medium composition. Glucose, yeast-powder and pH were significant for fermentation. 15.4g glucose and 5.32g yeast-powder per liter and pH 4.61 were optimum for the biomass accumulation from 2.75g/l to 6.88g/l, while 15.78g glucose and 5.86g yeast-powder per liter and pH 4.48 were optimum for EPS production from 0.214g/l to 0.751g/l. Under the optimized cultivation condition, cultivation kinetic models were studied in flask (pellet growth form) and airlift (filamentous growth form) reactors. The two morphologies resulted in different culture processes and mathematical models.
Keywords: Lentinus edodes; Statistical optimization; Biomass; Exo-polysaccharide; Morphology; Growth kinetics
Migration of reactive trace compounds from Novozym® 435 into organic solvents and ionic liquids by Hua Zhao; Zhiyan Song (pp. 113-118).
The commercial form of immobilized Candida antarctica lipase B (CALB), known as Novozym® 435, is a catalyst routinely used in enzymatic reactions. However, we observed a number of compounds migrated from this enzyme preparation into organic solvents and ionic liquids (ILs). These compounds were further identified by GC–MS analysis as a mixture of 17 substances, including 5 major components: glycerol, benzoic acid, 2-hydroxyethyl benzoate, 2-hydroxyethyl sorbate, and sorbic acid. The importance of this discovery is that all five major compounds are reactive in the presence of CALB, especially the last four compounds are potential acyl donors in enzymatic (trans)esterification reactions. We then quantified the migration of these acyl donors into various aqueous solutions, organic solvents and ILs, and observed that the migration into polar organic solvents and ILs was rapid (10–30min). We also measured the reactivities of these acyl donors with 1-propanol in Novozym® 435-catalyzed (trans)esterifications. Our data suggest that the initial reaction rates of sorbic acid and sorbate ester were very fast; although the initial rates of benzoic acid and benzoate were much slower, their conversions into propyl benzoate were significant within 24h period. The presence of these compounds in Novozym® 435 may not have considerable impact on fast reactions involving high substrate concentrations, however, it is important to realize that these trace compounds may affect the enzyme activity, and may cause confusion during the analysis of enzymatic reactions.
Keywords: Biocatalysis; Extraction; Novozym; ®; 435; Ionic liquid; Enzyme; Immobilization
Development and characteristics of rapidly formed hydrogen-producing granules in an acidic anaerobic sequencing batch reactor (AnSBR) by Da-Wei Liang; Shiva S. Shayegan; Wun Jern Ng; Jianzhong He (pp. 119-125).
This study investigated the development and characteristics of rapidly formed hydrogen-producing granules (HPGs) in an acidic anaerobic sequencing batch reactor (AnSBR). When subjecting the AnSBR suspended sludge to heat-shock (80°C for 20min) and acidic pretreatment (pH 2.0 for 24h) subsequently, granules were formed within the first 10 days of the AnSBR operation at pH 5.5. After subsequent second time heat-shock of the granules on day 35, hydrogen yield increased significantly to 1.36mol-H2/mol-glucose with a headspace content of 65±7% and was stable during the next 60 days running of the AnSBR. A typical mature HPG showed 1.7±0.2mm in diameter and had an average settling velocity of 43m/h. The granules were comprised of uniform rod shaped bacteria with a non-layered structure and multiple cracks on the surface. Three pure cultures, Clostridium sp. HP2, HP4 and HP7, were obtained from the enriched HPGs. Among the three isolates, strain HP4 showed the highest hydrogen yield of 1.41 (mol-H2/mol-glucose) at a rate of 0.85L-H2/L/day (34.5mmol-H2/L/day). This study suggests that acid pretreatment, combining with the short settling time (30min) and large exchange ratio (60%) of effluent, is applicable for rapid formation of HPGs in the AnSBR, which provides a promising approach for biological hydrogen production from the organic wastewater.
Keywords: Biogas; Bio-hydrogen; Biofuel; Activated sludge; Hydrogen-producing granules; AnSBR
Preparation of highly purified chondroitin sulphate from skate ( Raja clavata) cartilage by-products. Process optimization including a new procedure of alkaline hydroalcoholic hydrolysis by Miguel A. Murado; Javier Fraguas; María I. Montemayor; José A. Vázquez; Pilar González (pp. 126-132).
The aim of this study is to optimize the different stages for the obtaining of chondroitin sulphate from skate cartilage by means of experimental designs and kinetic approaches. The results of the hydrolysis cartilage using papain and an enzymatic preparation from ray pancreas are compared. Moreover, the basic differences among enzymatic and chemical hydrolysis are identified. In order to reduce the aggressive treatments with strong alkalis a combined step of hydrolysis–precipitation in hydroalcoholic solution is also proposed. Thus, the combination of enzymatic and chemical hydrolysis, selective precipitation together with membranes technology lead to the formulation of a quick and highly efficient process (15%, w/w) with low consumption of reagents and high purity for the chondroitin sulphate ( I=99%) obtained.
Keywords: Chondroitin sulphate; Cartilage; Fish by-products; Waste upgrading; Skate; Hydroalcoholic precipitation; Ultrafiltration; Mathematical modelling
Interfacial gas–liquid transfer area in alkane–aqueous dispersions and its impact on the overall volumetric oxygen transfer coefficient by L.D.C. Correia; C. Aldrich; K.G. Clarke (pp. 133-137).
KL a and gas–liquid interfacial area per unit volume were quantified in 2.5–20% n-C10–13 aqueous dispersions agitated at 600–1200rpm. The interfacial area was quantified using high speed photography and image analysis. Interfacial area correlated strongly with KL a over all agitation rates and alkane concentrations, suggesting that the interfacial area was the major factor defining KL a in these dispersions.The bubble diameter and gas hold up were identified as key parameters defining an optimal KL a at 5% alkane at agitation rates of 800–1200rpm, through their impact on the interfacial area. Decreased bubble diameter and increased gas hold up with alkane addition from 2.5% to 5% resulted in increased interfacial area. However, a decreased gas hold up on alkane addition above 5% resulted in a correspondingly decreased interfacial area, despite the continued decline in bubble diameter. The decrease in bubble diameter and the decrease in gas hold up have in part been attributed to the reduction of surface tension from 26.0 to 17.7 and the doubling of viscosity to 2.0mN/m respectively over the range of alkane concentrations examined.
Keywords: Alkane bioprocesses; Overall volumetric oxygen transfer coefficient; Interfacial transfer area; Sauter mean diameter; Gas hold up; Fluid properties
Fermentative production ofl-lactic acid from hydrolysate of wheat bran by Lactobacillus rhamnosus by Zheng Li; Lu Han; Yizhi Ji; Xiaonan Wang; Tianwei Tan (pp. 138-142).
To reduce the nutrient cost ofl-lactic acid production, wheat bran was chosen as a nutrient source. Various pretreatment processes were investigated, and 80°C for 20h by acid-hydrolysis was a suitable method considering the energy consumption. Pretreated wheat bran showed a better performance than that without treatment, especially forl-lactic acid yield (0.99g/g). Moreover, when 25g/l wheat bran hydrolysate was combined with 30g/l corn steep liquor, thel-lactic acid fermentation efficiency (yield 0.99g/g, productivity 3.75g/l/h) was even higher than that of the control with 15g/l yeast extract (yield 0.95g/g, productivity 2.46g/l/h). Although much more wheat bran hydrolysate and corn steep liquor were used than yeast extract in total amount, the cost of nitrogen in fermentation was estimated to be ¥1286/tl-lactic acid (25g/l wheat bran hydrolysate and 30g/l corn steep liquor), which is only 11% of the ¥11471/tl-lactic acid (15g/l yeast extract) in control test. Therefore, nutrients of wheat bran hydrolysate and corn steep liquor could be employed to substitute yeast extract forl-lactic acid production.
Keywords: l; -Lactic acid; Wheat bran; Biomass; Platform chemicals; Shake-flask; Stirred tank
Novel technique to control inner and outer diameter of calcium-alginate hydrogel hollow microfibers, and immobilization of mammalian cells by Takayuki Takei; Naoya Kishihara; Shinji Sakai; Koei Kawakami (pp. 143-147).
Calcium-alginate hydrogel hollow microfibers have a potential to be utilized in various fields such as tissue engineering. In this study, we developed a new technique for exquisite control of inner diameter (id) as well as outer diameter (od) of the microfibers using a coaxial triple cylinder. Aqueous solutions of dextran (core solution), sodium alginate (sample solution) and CaCl2 (sheath solution) were extruded simultaneously from the inner, intermediate and outer cylinders, respectively. The ratio of id to od could be controlled only by the ratio of flow volume of core solution to total flow volume of core and sample solutions (core volume ratio). The od depended on core volume ratio, flow velocities of core and sample solution at the tip of the intermediate cylinder, tip id of intermediate cylinder and flow velocity of sheath solution. Two types of mammalian cells could be separately located in the hollow core and the gel part of the microfibers. We confirmed that the cell-enclosing process scarcely influenced the viability of the enclosed cells. Although we did not perform long-term culture of the cell-enclosing microfibers in this study, these results indicate that our system has a high potential to fabricate biomimetic scaffold for tissue-engineered tubular tissues.
Keywords: Hollow microfiber; Alginate hydrogel; Coaxial triple cylinder; Co-flowing stream; Tubular tissue; Tissue engineering