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Applied Biochemistry and Biotechnology: Part A: Enzyme Engineering and Biotechnology (v.122, #1-3)
Surfactin production from potato process effluent by Bacillus subtilis in a chemostat by Karl S. Noah; Debby F. Bruhn; Gregory A. Bala (pp. 465-473).
The biosurfactant surfactin has potential to aid in the recovery of energy resources (oil recovery) or subsurface organic contaminants (environmental remediation). However, high medium and purification costs limit its use in these high-volume applications. In previous work, we showed that surfactin could be produced from an inexpensive low-solids potato process effluent with minimal amendments or pretreatments. Previous research has also shown that surfactin can be both produced in Bacillus subtilis cultures and recovered by foam fractionation in an airlift reactor. Results using both purified potato starch and unamended low-solids potato process effluent as substrates for surfactin production indicate that the process is oxygen limited and that recalcitrant indigenous bacteria in the potato process effluent hamper continuous surfactin production. The research reported here features the use of a chemostat operated in batch mode for producing surfactin with concomitant use of antifoam to prevent surfactant loss. The antifoam did not interfere with surfactin recovery by acid precipitation or its efficacy. Initial trials took about 48 h to produce 0.9 g/L of surfactin from potato process effluent. Increasing the oxygen mass transfer by increasing the stirring speed and adding a baffle decreased production time to 12–24 h and produced about 0.6 g/L of surfactin from two different potato-processing facilities.
Keywords: Bacillus subtilis ; biosurfactant; surfactin; alternate feedstock; enhanced oil recovery
Effects of nutrient supplements on simultaneous fermentation of nisin and lactic acid from cull potatoes by Chuanbin Liu; Yan Liu; Shulin Chen (pp. 475-483).
The feasibility of using cull potatoes as substrate for the simultaneous production of nisin, a natural food preservative, and lactic acid, a raw material for biopolymer production, was studied. Cull potatoes are potato tubers unacceptable for food processing because ofsize or damage caused by bruising or disease. Although cull potatoes are enriched in various nutrients including starch, minerals, and proteins, they alone still cannot provide enough essential nutrients for the growth and metabolism of Lactococcus lactis subsp. lactis (ATCC 11454). Stimulation of bacterial growth, nisin biosynthesis, as well as lactic acid production was observed when additional nutrients such as yeast extract, peptone from meat, peptone from soy (PS), corn steep solid (CSS), and distillers’ dried grains with solubles were provided. Considering the cost and availability, PS and CSS were selected as nutrient supplements for nisin and lactic acid coproduction. The conditions for nisin biosynthesis and lactic acid coproduction by L. lactis subsp. lactis in a cull potato-based medium were subsequently optimized using a statistically based experimental design.
Keywords: Nisin; lactic acid; cull potato; fermentation; optimization
Effect of reduction in yeast and enzyme concentrations in a simultaneous-saccharification-and-fermentation-based bioethanol process by Anders Wingren; Mats Galbe; Christian Roslander; Andreas Rudolf; Guido Zacchi (pp. 485-499).
The ethanol production cost in a simultaneous saccharification and fermentation-based bioethanol process is influenced by the requirements for yeast production and for enzymes. The main objective of this study was to evaluate—technically and economically—the influence of these two factors on the production cost. A base case with 5 g/L of baker’s yeast and an initial concentration of water-insoluble solids of 5% resulted in an experimental yield of 85%. When these data were implemented in Aspen Plus, yeast was assumed to be produced from sugars in the hydrolysate, reducing the overall ethanol yield to 69%. The ethanol production cost was 4.80 SEK/L (2.34 US$/gal). When adapted yeast was used at 2 g/L, an experimental yield of 74% was achieved and the estimated ethanol production cost was the same as in the base case. A 50% reduction in enzyme addition resulted in an increased production cost, to 5.06 SEK/L (2.47 US$/gal) owing to reduced ethanol yield.
Keywords: Ethanol; economics; process; simultaneous saccharification and fermentation; yeast; enzymes
Stability of recombinant green fluorescent protein (GFPuv) in glucose solutions at different concentrations and pH values by Thereza Christina Vessoni Penna; Marina Ishii; Juliana Sayuri Kunimura; Olivia Cholewa (pp. 501-527).
The stability at room temperature (25°C) of recombinant green fluorescent protein (GFPuv), expressed by Escherichia coli cells and isolated by three-phase partitioning extraction with hydrophobic interaction column, was studied. The GFPuv was diluted in buffered (each 10 mM: Tris-HCl, pH 8.0; phosphate, pH 6.0 and 7.0 and acetate, pH 5.0) and in unbuffered (water for injection [WFI]; pH 6.70 ± 0.40) glucose solutions (from 1.5 to 50%). By assaying the loss of fluorescence intensity as a measure of denaturation, the stability of GFPuv in these solutions was evaluated relative to glucose concentration, pH, osmolarity, density, conductivity, and viscosity. The extent of protein denaturation (loss of fluorescence intensity) was expressed in decimal reduction time (D-value), the time required to reduce 90% of the initial fluorescence intensity of GFPuv. The D-value between 56 and 83 h of GFPuv at 1.5–15% glucose in WFI was equivalent to 20–30% glucose in a phosphate. The stability of GFPuv in 50% glucose was similar for all buffers studied and four times higher than in WFI. By the convenient measure of fluorescence intensity, GFPuv can be used as an indicator to report the extent of denaturation rates of other proteins in glucose solutions.
Keywords: Protein stability; decimal reduction time; green fluorescent protein; glucose solution; denaturation; conductivity
Lactic acid production from cheese whey by immobilized bacteria by Abolghasem Shahbazi; Michele R. Mims; Yebo Li; Vestal Shirley; Salam A. Ibrahim; Antrison Morris (pp. 529-540).
The performance of immobilized Bifidobacterium longum in sodium alginate beads and on a spiral-sheet bioreactor for the production of lactic acid from cheese whey was evaluated. Lactose utilization and lactic acid yield of B. longum were compared with those of Lactobacillus helveticus. B. longum immobilized in sodium alginate beads showed better performance in lactose utilization and lactic acid yield than L. helveticus. In the spiral-sheet bioreactor, a lactose conversion ratio of 79% and lactic acid yield of 0.84 g of lactic acid/g of lactose utilized were obtained during the first run with the immobilized L. helveticus. A lactose conversion ratio of 69% and lactic acid yield of 0.51 g of lactic acid/g of lactose utilized were obtained during the first run with immobilized B. longum in the spiral-sheet bioreactor. In producing lactic acid L. helveticus performed better when using the Spiral Sheet Bioreactor and B. longum showed better performance with gel bead immobilization. Because B. longum is a very promising new bacterium for lactic acid production from cheese whey, its optimum fermentation conditions such as pH and metabolic pathway need to be studied further. The ultrafiltration tests have shown that 94% of the cell and cheese whey proteins were retained by membranes with a mol wt cutoff of 5 and 20 KDa.
Keywords: Cheese whey; bifidobacteria; immobilized cell; lactose; lactic acid; membrane; fermentation
Enhancing cellulase foam fractionation with addition of surfactant by Vorakan Burapatana; Ales Prokop; Robert D. Tanner (pp. 541-552).
Foam fractionation cannot be used to recover cellulase from an aerated water solution effectively because cellulase by itself can produce only a small amount of foam. The addition of a surfactant can, however, increase the foamate volume and enhance the concentration of cellulase. We studied three detergents individually added to a 200 mg/L cellulase solution to promote foaming. These detergents were anionic, cationic, and nonionic surfactants, respectively. Although contributing to foam production, it was observed that nonionic surfactant (Pluronic F-68) barely concentrated cellulase, leaving the enrichment ratio unchanged, near 1. With anionic surfactant, sodium dedecyl sulfate, and cationic surfactant, cetyltrimethylammonium bromide (CTAB), the enrichment ratio became much larger, but cellulase denaturation occurred, reducing the activity of the enzyme. When CTAB was used to help foam cellulase, β-cyclodextrin was subsequently added to the foamate to help restore the enzyme activity.
Keywords: Foam fractionation; surfactant; cellulase; cyclodextrin; denaturation
Optimization of alkaline transesterification of soybean oil and castor oil for biodiesel production by Débora de Oliveira; Marco Di Luccio; Carina Faccio; Clarissa Dalla Rosa; João Paulo Bender; Nádia Lipke; Cristiana Amroginski; Cláudio Dariva; José Vladimir de Oliveira (pp. 553-560).
This article reports experimental data on the production of fatty acid ethyl esters from refined and degummed soybean oil and castor oil using NaOH as catalyst. The variables investigated were temperature (30–70°C), reaction time (1–3 h), catalyst concentration (0.5–1.5 w/wt%), and oil-to-ethanol molar ratio (1:3–1:9). The effects of process variables on the reaction conversion as well as the optimum experimental conditions are presented. The results show that conversions >95% were achieved for all systems investigated. In general, an increase in reaction temperature, reaction time, and in oil-to-ethanol molar ratio led to an enhancement in reaction conversion, whereas an opposite trend was verified with respect to catalyst concentration.
Keywords: Alcoholysis; soybean oil; castor oil; alkaline catalyst; biodiesel
Cellulase production by Trichoderma reesei using sawdust hydrolysate by Chi-Ming Lo; Qin Zhang; Patrick Lee; Lu-Kwang Ju (pp. 561-573).
Sawdust hydrolysates were investigated for their ability to support cell growth and cellulase production, and for potential inhibition of Trichoderma reesei Rut C30. Simultaneous fermentations were conducted to compare the hydrolysate-based media with the controls having equivalent concentrations of glucose and Avicel cellulose. Six hydrolysates differing in the boiling durations in the hydrolysis procedure were evaluated. The hydrolysates were found to support cell growth and induce active cellulase synthesis. The maximum specific cellulase production rate was 0.046 filter paper units (FPU)/(g of cells · h) in the hydrolysate-based systems, much higher than that (0.017 FPU/[g of cells · h]) in the controls.
Keywords: Acid hydrolysis; cellulase; induction; inhibition; Trichoderma reesei
Effects of fatty acids on growth and poly-3-hydroxybutyrate production in bacteria by K. W. Lo; H. Chua; H. Lawford; W. H. Lo; Peter H. F. Yu (pp. 575-580).
The effects of saturated and unsaturated fatty acids (lauric acid, palmitic acid, steric acid, oleic acid, linoleic acid, soybean oil) on Sphaerotilus natans, 0B17 (Pseudomonas sp.), and recombinant Escherichia coli DH5(/pUC19/CAB were studied. Oleic acid enhances Poly-3-hydroxybutyrate (PHB) production in these three bacterial strains, suggesting that the single double bond of the acid activates the polyhydroxylkanoate accumulation enzymatic reaction. Under the effect of lauric acid and linoleic acid, the growth of S. natans and 0B17 were totally inhibited. However, the enhanced PHB accumulation in recombinant E. coli was observed.
Keywords: Fatty acids; poly-3-hydroxybutyrate; Sphaerotilus natans ; recombinant Escherichia coli ; Pseudomonas sp.
Performance of an internal-loop airlift bioreactor for treatment of hexane-contaminated air by Fernando J. S. Oliveira; Francisca P. de França (pp. 581-591).
Hexane is a toxic volatile organic compound that is quite abundant in gas emissions from chemical industries and printing press and painting centers, and it is necessary to treat these airstreams before they discharge into the atmosphere. This article presents a treatment for hexane-contaminated air in steady-state conditions using an internal-loop airlift bioreactor inoculated with a Pseudomonas aeruginosa strain. Bioprocesses were conducted at 20-mL/min, a load of 1.26 g/m3 of C6H14, and a temperature of 28°C. The results of hexane removal efficiencies were presented as a function of the inoculum size (approx 0.07 and 0.2 g/L) and cell reuse. Bioprocess monitoring comprises quantification of the biomass, the surface tension of the medium, and the hexane concentration in the fermentation medium as well as in the inlet and outlet airstreams. The steady-state results suggest that the variation in inoculum size from 0.07 to 0.2 g/L promotes hexane abatement from the influent from 65 to 85%, respectively. Total hydrocarbon removal from the waste gas was achieved during experiments conducted using reused cells at an initial microbial concentration of 0.2 g/L.
Keywords: Air treatment; hydrocarbons; hexane biodegradation; airlift bioreactor; Pseudomonas aeruginosa
Increase in removal of polycyclic aromatic hydrocarbons during bioremediation of crude oil-contaminated sandy soil by Fernando J. S. Oliveira; Francisca P. De França (pp. 593-603).
A 23 full factorial experimental design was adopted to estimate the effects of three variables on the biodegradation of oil during soil bioremediation: bioaugmentation seeding a mixed culture, addition of fertilizer or mineral media, and correction of initial pH of the soil to 7.0. The tests were carried out in polyvinyl chloride reactors with 5.0 kg of crude oil-contaminated soil at 14 g/kg. After screening the variables, soil bioremediation tests were conduced with varied C:N ratios, yielding an increase in biodegradation of the oil heavy fraction from 24 to 65%, consumption of total n-paraffins, and a remarkable decrease in the concentration of residual polycyclic aromatic hydrocarbons of the soil.
Keywords: Soil bioremediation; crude oil; hydrocarbons; biodegradation; experimental design
Recovery of organic acids from fermentation broths by Tim Eggeman; Dan Verser (pp. 605-618).
Rising concerns over the use of fossil resources have generated renewed interest in the production of commodity chemicals via fermentation. Organic acids are a particularly attractive target because their functionality enables downstream catalytic upgrading to a variety of compounds. In this article, we survey how common technical issues are addressed in the recovery schemes for several organic acids. We present results for the recovery of acetate using a new method based on amine complexation. Our reactive separation scheme produces a high-purity product, is energy efficient, and avoids the coproduction of a waste salt coproduct, all prerequisites for a large-scale production process.
Keywords: Organic acid recovery; acetic acid recovery; indirect ethanol process; gypsum; citric acid
Production of nisin by Lactococcus lactis in media with skimmed milk by Thereza Christina Vessoni Penna; Angela Faustino Jozala; Letícia Célia De Lencastre Novaes; Adalberto Pessoa Jr.; Olivia Cholewa (pp. 619-637).
Nisin is a bacteriocin that inhibits the germination and growth of Gram-positive bacteria. With nisin expression related to growth conditions of Lactococcus lactis subsp. lactis, the effects of growth parameters, media components, and incubation time were studied to optimize expression. L. lactis ATCC 11454 was grown (100 rpm at 30°C for 36 h) in both M17 and MRS standard broth media (pH 6.0–7.0) supplemented with sucrose (1.0–12.5 g/L), potassium phosphate (0.13 g/L), asparagine (0.5 g/L), and sucrose (0.24 g/L), and diluted 1:1 with liquid nonfat milk. Liquid nonfat milk, undiluted, was also used as another medium (9% total solids, pH 6.5). Nisin production was assayed by agar diffusion using Lactobacillus sake ATCC 15521 (30°C for 24 h) as the sensitive test organism. The titers of nisin expressed and released in culture media were quantified and expressed in arbitrary units (AU/L of medium) and converted into known concentrations of “standard nisin” (Nisaplin®, g/L). The detection of nisin activity was <0.01 AU/L in M17 and MRS broths, and 7.5 AU/L in M17 with 0.14% sucrose or 0.13% other supplements, and the activity increased to 142.5 AU/L in M17 diluted with liquid nonfat milk (1:1). The 25% milk added to either 25% M17 or 25% MRS provided the highest levels of nisin assayed.
Keywords: Nisin; Lactococcus lactis ; growth conditions; skimmed milk; Lactobacillus sake
Enhancing design of immobilized enzymatic microbioreactors using computational simulation by Robert Bailey; Frank Jones; Ben Fisher; Bill Elmore (pp. 639-652).
In continuous-flow enzymatic microbioreactors, enzymes on the channel walls catalyze reaction(s) among feed chemicals, resulting in the production of some desirable material or the destruction of some undesirable material. Computational models of microbioreactors were developed using the CFD-ACE+ multiphysics simulation package. These models were validated via comparison with experimental data for the destruction of urea, catalyzed by urease. Similar models were then used to assess the impact of internal features on destruction efficiency. It was found that triangular features within the channels enhanced the destruction efficiency more than could be attributed to the increase in surface area alone.
Keywords: Numerical modeling; microreactor; enzyme; urea; polydimethylsiloxane; destruction efficiency
Estimation of bioreactor efficiency through structured hydrodynamic modeling case study of a Pichia pastoris fed-batch process by Frank Delvigne; Thami El Mejdoub; Jacqueline Destain; Jean-Marc Delroisse; Micheline Vandenbol; Eric Haubruge; Philippe Thonart (pp. 653-671).
In this article, two theories are unified to investigate the effect of hydrodynamics on a specific bioprocess: the network-of-zones (NOZ) hydrodynamic structured modeling approach (developed by several researchers but applied to only a few bioprocesses) and the effectiveness factor η approach. Two process scales were investigated (20 and 500 L), and for each, hydrodynamics were quantified using an NOZ validated by homogeneity time measurements. Several impeller combinations inducing quite different hydrodynamics were tested at the 20-L scale. After this step, effectiveness factors were determined for each fermentation run. To achieve this, a perfectly mixed microbial kinetic model was evaluated by using simple Monod kinetics with a fed-batch mass balance. This methodology permitted determination of the effectiveness factor with more accuracy because of the relation with the perfect case deduced from the Monod kinetics. It appeared that for the small scale, η decreased until reaching a value of approx 0.7 (30% from the ideal case) for the three impeller systems investigated. However, stirring systems that include hydrofoils seemed to maintain higher effectiveness factors during the course of the fermentation. This effect can be attributed to oxygen transfer performance or to homogenization efficiency exhibited by the hydrofoils. To distinguish the oxygen transfer from the homogenization component of the effectiveness factor, these phenomena were analyzed separately. After determining the evolution of ηO 2 linked to oxygen transfer for each of the fermentation runs, the NOZ model was employed to quantify substrate gradient appearance. After this step, another effectiveness factor, ηmix, related to mixing was defined. Consequently, it is possible to distinguish the relative importance of the mixing effect and oxygen transfer on a given bioprocess. The results have highlighted an important scale effect on the bioprocess that can be analyzed using the NOZ model.
Keywords: Network-of-zones; effectiveness factors; oxygen transfer; mixing effect; gradient; impeller; homogeneity time
Sugarcane bagasse as raw material and immobilization support for xylitol production by Júlio C. Santos; Ícaro R. G. Pinto; Walter Carvalho; Ismael M. Mancilha; Maria G. A. Felipe; Silvio S. Silva (pp. 673-683).
Xylose-to-xylitol bioconversion was performed utilizing Candida guillier-mondii immobilized in sugarcane bagasse and cultured in Erlenmeyer flasks using sugarcane bagasse hydrolysate as the source of xylose. Fermentations were carried out according to a factorial design, and the independent variables considered were treatment, average diameter, and amount of bagasse used as support for cell immobilization. By increasing the amount of support, the xylitol yield decreased, whereas the biomass yield increased. The diameter of the support did not influence xylitol production, and treatment of the bagasse with hexamethylene diamine prior to fermentation resulted in the highest amount of immobilized cells.
Keywords: Xylitol; cell immobilization; sugarcane bagasse; Candida guilliermondii ; hemicellulosic hydrolysate
Removing proteins from an aerated yeast fermentation by pulsing carbon dioxide by Ryan A. Kirkland; Robert D. Tanner (pp. 685-693).
Salting-out is a common technique used for precipitating proteins and other materials from fermentation and tissue culture processes. It leaves a salt residue in the system. Foam fractionation can also be used to remove proteins by protein precipitation from a dilute solution. In doing so, there is usually a trade-off between enrichment and recovery. An increase in the airflow rate will increase the recovery, but only at the expense of the enrichment. A new method for increasing the recovery in foam fractionations and in yeast fermentations is to add a burst of CO2 to the process and then restore the air. This CO2 acts like a temporary salt, but it does not leave behind a residue. The recovery increases as a result of the joint use of these gases, perhaps by more than 10-fold, without sacrificing the enrichment. Chicken egg albumin in a foam fractionation column can serve as a simple, experimental model for the proposed recovery process in lieu of the fermentation process.
Keywords: Salting-out; foam fractionation; yeast fermentation; protein concentration; chicken egg albumin
Ceriporiopsis subvermispora used in delignification of sugarcane bagasse prior to soda/anthraquinone pulping by Sirlene M. Costa; Adilson R. Gonçalves; Elisa Esposito (pp. 695-706).
Sugarcane bagasse was pretreated with the white-rot fungus Ceriporiopsis subvermispora for 30 d of incubation. The solid-state fermentation of 800 g of bagasse was carried out in 20-L bioreactors with an inoculum charge of 250 mg of fungal mycelium/kg of bagasse. The oxidative enzymes manganese peroxidase (MnP), lignin peroxidase (LiP), and lac-case (Lac) and the hydrolytic enzyme xylanase (Xyl) were measured by standard methods and related to the fungus’s potential for delignification. Among the lignocellulolytic assayed enzymes, Xyl was detected in larger quantity (4478 IU/kg), followed by MnP (236 IU/kg). LiP and Lac were not detected. The results of chemical analysis and mass component loss showed that C. subvermispora was selective to lignin degradation. Pretreated sugarcane bagasse and control pulps were obtained by soda/anthraquinone (AQ) pulping. Pulp yields, kappa number, and viscosity of all pulps were determined by chemical analysis of the samples. Yields of soda/AQ ranged from 46 to 54%, kappa numbers were 15–25, and the viscosity ranged from 3.6 to 7 cP for pulps obtained from pretreated sugarcane bagasse.
Keywords: Ceriporiopsis subvermispora ; sugarcane bagasse; selective biodegradation; hydrolytic enzymes; oxidative enzymes; soda/anthraquinone pulping; lignin
The two-phase water/silicon oil bioreactor prospects in off-gas treatment by Jean-Marc Aldric; Jacqueline Destain; Philippe Thonart (pp. 707-719).
Research was carried out to develop a biphasic biologic reactor able to clean the gas effluents polluted by volatile organic compounds. Initially, Rhodococcus erythropolis T 902.1 was selected on the basis of its capacity to degrade isopropylbenzene (IPB). The effect of gas flow and IPB concentration on the biodegadation of IPB was evaluated. The results show that the use of silicon oil allows large quantities of IPB to be absorbed within the medium of biologic abatement. On the other hand, the biodegradation rate was directly correlated to the inlet flow of IPB. Thus, the reactor presents interesting opportunities for the biologic treatment of gas effluents.
Keywords: Two-phase bioreactor; silicon oil; volatile organic compounds; off-gas treatment
Leaf protein from ammonia-treated dwarf elephant grass (Pennisetum purpureum) schum cv. mott) by Lauris Urribarrí; Alexis Ferrer; Alejandro Colina (pp. 721-730).
Proteins can be an excellent by product of the biorefining of lignocellulosic materials. In this work, extraction conditions for the white leaf proteins (cytoplasmic) of ammonia-treated dwarf elephant grass were established to obtain a protein juice suitable for the production of leaf protein concentrates. A calcium hydroxide solution was used as extracting agent, at several solid-liquid ratios, pHs, temperatures, and times. Extractions were carried out in Erlenmeyer flasks containing 5 g (dry basis) of forage with constant agitation (100 rpm). The soluble protein content was determined by the Lowry method. Optimal extraction conditions for the ammonia-treated forage were 12.60 pH, 1:10 solid-liquid ratio, 90°C, and 30 min extraction time, resulting in 52.65% extraction yield. The ammonia treatment significantly increased (p<0.05) the release of proteins from the fibrous matrix, facilitating their extraction.
Keywords: Leaf proteins; ammonia; dwarf elephant grass; extraction
Microbial synthesis and characterization of physiochemical properties of polyhydroxyalkanoates (PHAs) produced by bacteria isolated from activated sludge obtained from the municipal wastewater works in Hong Kong by Ma Tsz-Chun; P. L. Chan; H. Lawford; H. Chua; W. H. Lo; Peter Hoifu Yu (pp. 731-739).
The first objective of this study was the measurement of physical properties of P(3HB-co-3HV) copolymers with different (hydroxybutyrate) HB to (hydroxyvalerate) HV ratios produced by Bacillus cereus (TRY2) isolated from activated sludge. The 3HV PHBV copolymers were 0.05, 22.6, 39.2, 54.1, and 69.1 mol%, respectively. The second objective was to study possible wastewater treatment and production of PHAs at the same time by B. cereus (TRY2) and Pseudomonas spp. (TOB17) (both were isolated from activated sludge), recombinant Bacillus DH5α, and a combination of the above three bacteria. The results were satisfactory; the maximum COD and TOC of the sewage sludge reduced were 53.5% and 67.5%, respectively.
Keywords: Activated sludge; Bacillus cereus ; PHA; Pseudomonas spp.; wastewater treatment
Optimization of acid hydrolysis of sugarcane bagasse and investigations on its fermentability for the production of xylitol by Candida guilliermondii by Rafael Fogel; Rafaela Rodrigues Garcia; Rebeca da Silva Oliveira; Denise Neves Menchero Palacio; Luciana da Silva Madeira; Nei Pereira Jr. (pp. 741-752).
The dilute-acid hydrolysis of sugarcane bagasse was optimized using a statistical experimental design resulting in hydrolysates containing 57.25 g/L of xylose, which were fermented with a high inoculum concentration (10 g/L of the yeast Candida guilliermondii IM/UFRJ 50088). The addition of urea reduced the time of conversion (t C) to 75 h (without nitrogen source addition t C>127 h), and, consequently, improving the rates of xylitol bioproduction. Fermentator experiments, using the optimized conditions, resulted in enhanced conversion rates, reducing t C to 30 h. The stability of the yeast in the hydrolysate was also verified in a 480-h cultivation.
Keywords: Sugarcane bagasse; dilute-acid hydrolysis optimization; sugarcane bagasse hydrolysate; xylitol; bioproduction
Production of hyaluronic acid by Streptococcus by C. S. Ogrodowski; C. O. Hokka; M. H. A. Santana (pp. 753-761).
The effects of the addition of lysozyme and forced aeration on the rheological properties and production of hyaluronic acid by Streptococcus zooepidemicus were investigated. Lysozyme was added to the culture broth in two pulses during the exponential and stationary phases of a fermentation carried out in a rotary shaker (150 rpm), using 200 mL Erlenmeyer flasks. The effect of aeration was evaluated by feeding air into a 2.5 L fermentor at a 2 vvm rate. The effects were analyzed in terms of concentration, viscosity, viscoelasticity, and molecular weight of the hyaluronic acid produced.
Keywords: Hyaluronic acid; fermentation; Streptococcus ; lysozyme and aeration