Lactic acid engineering

Special mention must be made of poly(lactic acid), a biodegradable/bio-resorbable polyester, obtained from renewable resources through fermentation of com starch sugar. This polymer can compete with conventional thermoplastics such as PET for conventional textile fibers or engineering plastics applications. Hie first Dow-Cargill PLA manufacturing facility is scheduled to produce up to 140,000 tons of Nature Works PLA per year beginning in 200245 at an estimated price close to that of other thermoplastic resins U.S. l/kg.46 Other plants are planned to be built in the near future.45... 

The chemical engineering approach began with an analysis of the biochemistry of platelet metabolism. Like many cells, platelets consume glucose by two pathways, an oxidative pathway and an anaerobic pathway. The oxidative pathway produces carbon dioxide, which makes the solution containing the platelets more acidic (lower pH) and promotes anaerobic metabolism. This second metabolic pathway produces large amounts of lactic acid, further lowering pH. The drop in pH from both pathways kills the platelets. 

Watanabe J, Nederberg F, Atthoff B et al (2007) Cytocompatible biointerface on poly(lactic acid) by enrichment with phosphorylcholine groups for cell engineering. Mater Sci Eng 27 227-231... 

Watanabe J, Eriguchi T, Ishihara K (2002) Stereocomplex formation by enantiomeric poly (lactic acid) graft-type phospholipid polymers for tissue engineering. Biomacromolecules 3 1109-1114... 

Watanabe J, Ishihara K (2005) Cell engineering biointerface focusing on cytocompatibility using phospholipid polymer with an isomeric oligo(lactic acid) segment. Biomacromolecules 6 1797-1802... 

Hydroxypropionic Acid (3-HPA). Like the structurally isomeric lactic acid, 3-HPA constitutes a three-carbon building block with the potential of becoming a key intermediate for a variety of high-volume chemicals malonic and acrylic acids, methacrylate, acrylonitrile, 1,3-propanediol, and so forth.Thus, Cargill is developing a low-cost fermentation route by metabolic engineering of the microbial... 

These dendrimers expand the repertoire of polymers available for study. Current investigations are primarily limited to linear polymers that possess ill-defined solution structures and fewer hydroxyl groups for further modification. The introduction of biocompatible building blocks (e.g., glycerol and lactic acid) augments the favorable and already known physical properties of dendrimers. These properties are likely to facilitate the design of new materials for specific biomedical and tissue engineering applications. 

As an example of the application of the aforementioned sequence, Table XYI lists the main engineering parameters necessary to design or optimize ED stacks equipped with AMV and CMV electromembranes (Table II) and committed to the recovery of the sodium salts of some weak monocarboxylic acids of microbial origin (i.e., acetic, propionic, and lactic acid) and of a strong inorganic acid (i.e., chloride acid), as estimated by Fidaleo and Moresi (2005a,b, 2006). 

Kondo, K., Otono, T. and Matsumoto, M. (2004) Preparation of microcapsules containing extractants and the application of the microcapsules to the extractive fermentation of lactic acid. Journal of Chemical Engineering of Japan, 37, 1. 

Progress in the techniques of classical strain development and metabolic engineering (Box 24) have made a growing number of fermentation processes feasible and economically attradive. Beside the bulk amino acids, lactic acid, penicillins for the pharmaceutical market, and some vitamins, for example vitamin C (ascorbic acid... 

Another promising thermophilic Gram-positive microbe is Thermoanaero-bacterium saccharolyticum which ferments xylan and produces ethanol, acetate, lactic acid, CO2, and H2. The engineered strain TD1, in which the... 

Hugenholtz, J., and Kleerebezem, M. 1999. Metabolic engineering of lactic acid bacteria overview of the approaches and results of pathway rerouting involved in food fermentations. Curr. Op. Biotechnol., 10,492-497. 

Kleerebezemab, M., Hols, P., and Hugenholtz, J. 2000. Lactic acid bacteria as a cell factory rerouting of carbon metabolism in Lactococcus lactis by metabolic engineering. Enz. Microbial Technol., 26, 840-848. 

Nichols, N. N., Dien, B. S., and Bothast, R. J. 2003. Engineering lactic acid bacteria with pyruvate decarboxylase and alcohol dehydrogenase genes for ethanol production from Zymomonas mobilis. J. Ind. Microbiol. Biotechnol., 30, 315-321. 

Aarnikunnas et aL (2002) used metabolic engineering of L. fermentum for the production of mannitol and pure L-lactic acid or pyruvate. The authors first developed genetic tools to modify L. fermentum and then proceeded to inactivate first IdhD gene and then IdhL gene to create a bacterium that could produce mannitol and either pure L-lactic acid or pyruvic acid in a single process. In bioreactor cultivations, the single mutant strain constructed by... 

Aarnikunnas, I., von Weymarn, N., Ronnholm, K., Leisola, M., and Palva, A. 2002. Metabolic engineering of Lactobacillus fermentum for production of mannitol and pure L-lactic acid or pyruvate. Biotechnol. Bioeng., 82, 653-663. 

Fig. 3 Metabolic engineering for L-lactic acid production in Saccharomyces cerevisiae. The abbreviation of enzymes is described as follows LDH bovine lactate dehydrogenase, PDC pyruvate decarboxylase complex encoded by the genes PDC1, PDC5, and PDC6, which were deleted in this strategy...

When the initial shortcomings of these engineered yeasts, such as low stoichiometric yield and productivity, have been ironed out, it may be expected that lactic acid fermentation in an acidic medium, combined with solvent extraction of the product, will evolve into a procedure of unprecedented efficiency. 

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