The Experts below are selected from a list of 168 Experts worldwide ranked by ideXlab platform
N J Titchenerhooker - One of the best experts on this subject based on the ideXlab platform.
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a study of process interactions between cell disruption and debris clarification stages in the recovery of yeast intracellular products
Biotechnology Progress, 1993Co-Authors: Andrew I Clarkson, Patrick Lefevre, N J TitchenerhookerAbstract:The effects of varying the levels of cell disruption achieved by high-pressure homogenization upon subsequent centrifugal separation of cell debris have been defined by measuring sedimentation velocity distributions of the cell debris. Using this data together with particle size distributions, a computer-based model of a Disk Stack centrifuge has been used to predict the efficiency of centrifugal separation. These predictions have been compared with both laboratory scale and pilot plant scale experimental results. A similar sedimentation velocity technique has been used to characterize the properties of the flocs formed by addition of poly(ethylene imine) to a borax-clarified homogenate supernatant. The variations of floc settling properties with respect to polymer concentration are defined.
R. Salas-coronado - One of the best experts on this subject based on the ideXlab platform.
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Lipids rich in ω-3 polyunsaturated fatty acids from microalgae
Applied Microbiology and Biotechnology, 2016Co-Authors: N. F. Santos-sánchez, A. Torres-ariño, P. C. Guadarrama-mendoza, Rogelio Valadez Blanco, B. Hernández-carlos, R. Salas-coronadoAbstract:Despite microalgae recently receiving enormous attention as a potential source of biodiesel, their use is still not feasible as an alternative to fossil fuels. Recently, interest in microalgae has focused on the production of bioactive compounds such as polyunsaturated fatty acids (PUFA), which provide microalgae a high added value. Several considerations need to be assessed for optimizing PUFA production from microalgae. Firstly, a microalgae species that produces high PUFA concentrations should be selected, such as Nannochloropsis gaditana, Isochrysis galbana, Phaeodactylum tricornutum, and Crypthecodinium cohnii, with marine species gaining more attention than do freshwater species. Closed cultivation processes, e.g., photobioreactors, are the most appropriate since temperature, pH, and nutrients can be controlled. An airlift column with LEDs or optical fibers to distribute photons into the culture media can be used at small scale to produce inoculum, while tubular and flat panels are used at commercial scale. Depending on the microalgae, a temperature range from 15 to 28 °C and a pH from 7 to 8 can be employed. Relevant conditions for PUFA production are medium light irradiances (50–300 μmol photons m−2 s−1), air enriched with (0–1 % (v/v) CO2, as well as nitrogen and phosphorous limitation. For research purposes, the most appropriate medium for PUFA production is Bold’s Basal, whereas mixotrophic cultivation using sucrose or glucose as the carbon source has been reported for industrial processes. For cell harvesting, the use of tangential flow membrane filtration or Disk Stack centrifugation is advisable at commercial scale. Current researches on PUFA extraction have focused on the use of organic solvents assisted with ultrasound or microwaves, supercritical fluids, and electroporation or are enzyme assisted. Commercial-scale extraction involves mainly physical methods such as bead mills and expeller presses. All these factors should be taken into account when choosing a PUFA production system, as discussed in this review.
Wallace Woon-fong Leung - One of the best experts on this subject based on the ideXlab platform.
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Selection and Sizing of Centrifuges
Centrifugal Separations in Biotechnology, 2007Co-Authors: Wallace Woon-fong LeungAbstract:This chapter deals with the selection and the sizing of centrifuges for biotech applications. All centrifuges, such as spintube, Disk Stack, tubular, chamber bowl, and decanter can be scaled by the appropriate dimensionless Le number. However, the Le number depends on the specific set of geometric and operating parameters for each type of centrifuge. Based on this, one can determine the separated size of cell particles—the cut size. The cut size, which depends on the operation and the geometry of the machine, should be smaller than the size of cell that needs to be separated. If there are any changes in viscosity (from temperature change) or solids concentration, it affects the Le number from which the feed rate and the G-force need to be modified; otherwise, the cut size would be different and that affects the separation outcome. Sizings are made in centrifuges for use in small organelles (0.1-1 micron) and relatively larger biological cells (1-20 microns and bigger).
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Disk Stack Modeling
Centrifugal Separations in Biotechnology, 2007Co-Authors: Wallace Woon-fong LeungAbstract:This chapter presents a simple trajectory model on particle deposition in a Disk-Stack centrifuge. The flow in each channel formed between adjacent Disks is assumed as a plug flow. The model is validated against an experiment on cell separation using a Disk-Stack centrifuge. The results exhibit that suspension of cell culture contains viable mammalian cells 10-20 microns, non-viable cells 5-10 microns, and cell debris that are less than 5 microns. The suspension is separated in a pilot Disk-Stack centrifuge with a bowl diameter of about 190 mm. The cell debris and nonviable cells are removed in the centrate, and the viable cells are captured in the concentrate. The model presented in the chapter is used to simulate conditions that may not have experimental results or extend to conditions where experimental results are limited or lacking.
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4 – Disk Centrifuge
Centrifugal Separations in Biotechnology, 2007Co-Authors: Wallace Woon-fong LeungAbstract:Publisher Summary This chapter reviews the principle of inclined plate sedimentation. The same principle is extended to Disk-Stack centrifuge. The geometry of the Disk-Stack centrifuge is discussed. The adverse effect due to the Coriolis acceleration can be minimized with use of spacing bars, which oppose the flow driven by Coriolis and serve as spacing elements between adjacent Disks. In addition, manual dropping-bottom and nozzle Disks are described. Gentle acceleration of both the feed stream and the means of discharging the separated liquid streams converting the kinetic energy to pressure head are discussed. It also focuses on several illustrations on feed acceleration tests investigate a big contrast, both qualitatively and quantitatively, in the performance differences between a good and a poor feed accelerator. The chapter also discusses several other considerations, such as materials of construction, Clean-In-Place (CIP), steam sterilization, containment, surface finish, temperature control, water requirements, noise level, and explosion-proof design.
Eli Keshavarz-moore - One of the best experts on this subject based on the ideXlab platform.
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Prediction and verification of centrifugal dewatering of P. pastoris fermentation cultures using an ultra scale‐down approach
Biotechnology and Bioengineering, 2012Co-Authors: A.g. Lopes, Eli Keshavarz-mooreAbstract:Recent years have seen a dramatic rise in fermentation broth cell densities and a shift to extracellular product expression in microbial cells. As a result, dewatering characteristics during cell separation is of importance, as any liquor trapped in the sediment results in loss of product, and thus a decrease in product recovery. In this study, an ultra scale-down (USD) approach was developed to enable the rapid assessment of dewatering performance of pilot-scale centrifuges with intermittent solids discharge. The results were then verified at scale for two types of pilot-scale centrifuges: a tubular bowl equipment and a Disk-Stack centrifuge. Initial experiments showed that employing a laboratory-scale centrifugal mimic based on using a comparable feed concentration to that of the pilot-scale centrifuge, does not successfully predict the dewatering performance at scale (P-value
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Investigation of the impact of Tat export pathway enhancement on E. coli culture, protein production and early stage recovery.
Biotechnology and Bioengineering, 2011Co-Authors: Steven D. Branston, Cristina F.r.o. Matos, Robert B. Freedman, Colin Robinson, Eli Keshavarz-mooreAbstract:The twin arginine translocation (Tat) pathway occurs naturally in E. coli and has the distinct ability to translocate folded proteins across the inner membrane of the cell. It has the potential to export commercially useful proteins that cannot be exported by the ubiquitous Sec pathway. To better understand the bioprocess potential of the Tat pathway, this article addresses the fermentation and downstream processing performances of E. coli strains with a wild-type Tat system exporting the over-expressed substrate protein FhuD. These were compared to strains cell-engineered to over-express the Tat pathway, since the native export capacity of the Tat pathway is low. This low capacity makes the pathway susceptible to saturation by over-expressed substrate proteins, and can result in compromised cell integrity. However, there is concern in the literature that over-expression of membrane proteins, like those of the Tat pathway, can impact negatively upon membrane integrity itself. Under controlled fermentation conditions E. coli cells with a wild-type Tat pathway showed poor protein accumulation, reaching a periplasmic maximum of only 0.5 mg L−1 of growth medium. Cells over-expressing the Tat pathway showed a 25% improvement in growth rate, avoided pathway saturation, and showed 40-fold higher periplasmic accumulation of FhuD. Moreover, this was achieved whilst conserving the integrity of cells for downstream processing: experimentation comparing the robustness of cells to increasing levels of shear showed no detrimental effect from pathway over-expression. Further experimentation on spheroplasts generated by the lysozyme/osmotic shock method—a scaleable way to release periplasmic protein—showed similar robustness between strains. A scale-down mimic of continuous Disk-Stack centrifugation predicted clarifications in excess of 90% for both intact cells and spheroplasts. Cells over-expressing the Tat pathway performed comparably to cells with the wild-type system. Overall, engineering E. coli cells to over-express the Tat pathway allowed for greater periplasmic yields of FhuD at the fermentation scale without compromising downstream processing performance.
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A software tool for assessing the financial and technical impacts of changing industrial bio-manufacturing processes
2006Co-Authors: Sunil Chhatre, Richard Francis, Kieran O'donovan, T-h Nigel, Anthony R. Newcombe, Eli Keshavarz-mooreAbstract:Growing pressures in the bioprocess industries are driving the need for simulations that rapidly evaluate strategies for achieving improvements in large-scale production. This paper presents a prototype simulation that evaluates the financial and technical impacts of developing and implementing a range of manufacturing changes to a pre-existing industrial process. The simulation evaluates each option with respect to development costs and timescales as well as annual production mass, cost of goods and batch times. These metrics are integrated together using a multi-attribute decision making (MADM) technique to produce a single value that quantitatively evaluates each strategy. The methodology is applied to development strategies being considered for an industrial process operated by Protherics U.K. Limited that manufactures an FDA-approved polyclonal Fab preparation for the treatment of rattlesnake envenomation. In the current process, an ovine serum feed containing anti-venom lgG is subjected to sodium sulphate precipitation to sediment the antibodies. The precipitate is separated from the contaminating supernatant by Disk Stack centrifugation, after which the lgG molecules are enzymatically digested by papain into their Faband Fccomponents. The latter is removed from the process stream by passing it through an ion exchange column, after which the venom-specific Fab is recovered in an affinity step. Process changes considered include replacing the precipitation and centrifugation stages by a synthetic Protein A column step operating in either packed or expanded modes, eliminating the ion exchanger, raising the volume of the ovine feed and increasing the venom-specific IgG titre. Of all the changes examined, using an expanded bed column with the highest increase in lgG titre that could be achieved and the greatest feed volume that could be handled within the facility, combined with the elimination of the ion exchanger results in the best MADM-based value. This would therefore be the most desirable alternative to current operation.
C. Stewart Slater - One of the best experts on this subject based on the ideXlab platform.
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Life cycle assessment of dewatering routes for algae derived biodiesel processes
Clean Technologies and Environmental Policy, 2013Co-Authors: Daniel Connell, Mariano Savelski, C. Stewart SlaterAbstract:Biodiesel derived from algae is considered as a sustainable fuel, but proper downstream processing is necessary to minimize the environmental footprint of this process. Algae is grown in dilute liquid cultures, and achieving the low water contents required for extraction represents one of the greatest challenges for the production of algae derived biodiesel. An analysis of the life cycle emissions associated with harvesting, dewatering, extraction, reaction, and product purification stages for algae biodiesel were performed. This “base case” found 10,500 kg of total emissions per t of biodiesel with 96 % of those attributed to the spray dryer used for dewatering. Alternative cases were evaluated for various sequences of mechanical and thermal dewatering techniques. The best case, consisted of a Disk-Stack centrifuge, followed by the chamber filter press, and a heat integrated dryer. This resulted in 875 kg emissions/t of biodiesel, a 91 % reduction from the base case. Significant reductions in life cycle emissions were achieved for all mechanical dewatering alternatives compared to the base case, but further improvements using these existing technologies were limited. Additional improvements will require the development of new techniques for water removal or wet extractions.