Biomass fermentation lactic acid production

Continuous lactic acid production from whey permeate is carried out in a process that consists of three separate operations in (1) a bioreactor, (2) an ultrafiltered (UF) model, and (3) an ED cell. With the UF process, recycling of all or part of the biomass is achieved. It is also possible to separate low molecular weight metabolites, such as sodium lactate, resulting from lactose fermentation. This product can then be extracted and concentrated continuously by ED. A disadvantage of continuous lactic acid production is, however, that it tends to clog the ultrafiltration membranes, which restricts permeate flow (Bazinet, 2004). 

Chen, R. and Lee, Y.Y. 1997. Membrane-mediated extractive fermentation for lactic acid production from cellulosic biomass. Applied Biochemistry and Biotechnology 63 435-448. 

One of the most important processes in the production of biochemicals is the 40,000 tons/yr lactic acid production involving the Lactobacillus oxidation of lactose. The MBR productivity increased eightfold compared to a conventional batch reactor with a 19-fold increased biomass concentration. Even a 30-fold increased production of ethanol was found upon coupling the Saccharomyces cerevisiae fermentation to a membrane separation. Other successful industrial applications involve the pathogen-free production of growth hormones, the synthesis of homochiral cyanohydrins, the production of 1-aspartic acid, phenyl-acetylcarbinol, vitamin B12, and the bio transformation of acrylonitrile to acrylamide. 

The yield of 1,3-PD for this reaction is 67% (mol/mol). If biomass formation is considered the theoretical maximal yield reduces to 64%. In the actual fermentation a number of other by-products are formed, i. e., ethanol, lactic acid, succinic acid, and 2,3-butanediol, by the enterobacteria Klebsiella pneumoniae, Citrobacter freundii and Enterobacter agglomerans, butyric acid by Clostridium butyricum, and butanol by Clostridium pasteurianum (Fig. 1). All these by-products are associated with a loss in 1,3-PD relative to acetic acid, in particular ethanol and butanol, which do not contribute to the NADH2 pool at all. 

Extraction into capsules with a solvent, for example, recovery of phenylethanol (a product of phenylalanine bioconversion by yeast) [67] or lactic acid from fermentation broth [68], has attracted interest recently. The polymeric core of the capsule prevents direct contact of the solvent with biomass. This process could be regarded as a batch MBSE. 

Much has been written about Cargill Dow LLC s polylactide (PLA) polymer, also known as NatureWorks PLA. PLA is a thermoplastic produced from biomass sugars by fermentation. The fermentation product, lactic acid, is converted into a lactide that is purified and polymerized using a special ring-opening process (18). 

In order to decrease human consumption of petroleum, chemists have investigated methods for producing polymers from renewable resources such as biomass. Nature Works polylactic acid (PLA) is a polymer of naturally occurring lactic acid (LA), and LA can be produced from the fermentation of corn. The goal is to eventually manufacture this polymer from waste biomass. Another advantage of PLA is that, unlike most synthetic polymers which litter the landscape and pack landfills, it is biodegradable. PLA can also be easily recycled by conversion back into LA. It can replace many petroleum-based polymers in products such as carpets, bags, cups, and textile fibers. 

The anaerobic fermentation of lactic acid is traditionally performed at up to 50°C over 2-8 d at pH 5.5-6.5 (lactic acid bacteria are highly sensitive to acid). The pH is maintained by titration with a base, usually calcium carbonate. The product concentration is kept below approx. 100 g L 1 to prevent precipitation of calcium lactate, as the separation of a precipitate from the biomass would be too elaborate. The stoichiometric yields are high, of the order of 1.7-1.9 mol mob1 (85-95% of the theoretical yield) but the space-time yield, which is ap-... 

Several strains of photosynthetic bacteria were applied for H2 production from the lactic acid fermentate of C. reinhardtii biomass (Fig. 2). R. marinum (ATCC 35675) produced the largest amount of H2 (124 mmol) from 1/ of the culture over a period of 100 h. The molar yield of H2 by R. marinum from the starch accumulated in an algal biomass was 7.9 mol H2/mol starch-glucose. 

Figure 2 H2 production from the lactic acid fermentate of the C. reinhardtii biomass by various photosynthetic bacteria. The fermentate of C. reinhardtii biomass was diluted to give a lactic acid concentration of 30 mmol/1, inoculated with one of the five strain of photosynthetic bacteria (O, Rhodobacter sphaeroides A, Rhodobacter capsulata , Rhodospirillum rubrum 9, Rhodovulum sulfidophilus , Rhodobium marinum), and incubated under illumination of 330 W/m2 at 30°C.

Lactic acid is a major end product from fermentation of a carbohydrate by lactic acid bacteria (Tormo and Izco, 2004). However, lactic acid can be produced commercially by either chemical synthesis or fermentation. The chemical synthesis results in a racemic mixture of the two isomers whereas during fermentation an optically pure form of lactic acid is produced. However, this may depend on the microorganisms, fermentation substrates, and fermentation conditions. Lactic acid can be produced from renewable materials by various species of the fungus Rhizopus. This has many advantages as opposed to bacterial production because of amylolytic characteristics, low nutrient requirements, and the fungal biomass, which is a valuable fermentation by-product (Zhan, Jin, and Kelly, 2007). 

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