Production of Lactic Acid by Fermentation

Scientific progress in more recent times has not only revealed the mechanisms of traditional bioprocesses, but has also improved the ability of bioprocessing to generate useful products. Advances in pure culture and other classical bacteriological methods initiated the first commercial production of lactic acid by fermentation in 1881 The subsequent development of the first cholera,... 

The buffering capacity of milk is often estimated by determining its titratable acidity, which involves titrating a sample of milk, containing a suitable indicator (usually phenolphthalein), with NaOH and thus is a measure of the buffering capacity of the milk between its natural pH and the phenolphthalein endpoint (i.e. between about pH 6.6 and 8.3). Titratable acidity is normally used to estimate the freshness of milk and to monitor the production of lactic acid during fermentation. Fresh milk typically requires 1.3-2.0 milliequivalents OH to titrate 100ml from pH 6.6 to pH 8.3 (13-20 ml of 0.1 M NaOH), i.e. fresh milk has a titratable acidity of 0.14 to 0.16%, expressed as lactic acid. 

The highly flavorable compound diacetyl is an important by-product of lactic acid bacterial fermentation. The mechanism of its formation has recently been unraveled (35). Diacetyl (measured as diacetyl rather than as diacetyl plus acetoin) is present in higher concentrations in wines with malo-lactic fermentation (cf. Ref. 36). At approximately threshold levels, this compound might contribute favorably to the flavor of wine (7) since increased complexity has been shown to enhance the quality of wine (37). 

U.S. 6,475,759 (to Cargill, Inc.) describes fermentation of corn steep liquor to lactic acid, and U.S. 6,229,046 (also to Cargill, Inc.) describes recovery of lactic acid from the fermentation broth. What is the cost of production of lactic acid by this route ... 

Figure 7.3 Production of lactic acid by Rhizopus and simultaneous saccharification and fermentation (SSF) (Adapted from Zhang, Jin, and Kelly (2007). Biochemical Engineering Journal 35 251-263. With permission.)...

One example of fermentative bacteria is a group termed the lactic acid bacteria. These bacteria, which are commercially important in the cheese and dairy industry as well as in pickle and sauerkraut production, produce lactic acid by fermenting sugars. 

Chatterjee, M., Chakrabarty, S., Chattopadhyay, B., and Mandal, R. (1997) Production of lactic acid by direct fermentation of starchy wastes by an amylase-producing Lactobacillus. Biotechnol. Lett., 19, 873-874. 

D-Lactide can be obtained if one has the appropriate biochemistry to produce the D-enantiomer of lactic acid by fermentation of carbohydrates. Copolymeiization of controlled mixtures of l- and D-lactides subsequently offers the advantage of precise control over PLA properties. Moreover, D-lactide is the monomer for the production of poly(D-lac-tide), which is able to form high-melting stereocomplex PLA via 1 1 racemic cocrystallization with P(L)LA, as will be discussed in Chapter 5 [89]. 

Lee RK, Ryu HW, Oh H, Kim M, Wee YJ (2014) Cell-recycle continuous fermentation of Enterococcus faecalis RKYl for economical production of lactic acid by reduction of yeast extract supplementation. J Microbiol Biotechnol 24 661-666. doi 10.4014/jmb. 1402.02017 Leiss S, Venus J, Kamm B (2010) Fermentative production of L-Lysine-L-lactate with fractionated press juices from the green biorelinery. Chem Eng Technol 33(12) 2102-2105. doi 10. 1002/ceat.201000314... 

Several carbohydrates such as corn and potato starch, molasses and whey can be used to produce lactic acid. Starch must fust be hydrolysed to glucose by enzymatic hydrolysis then fermentation is performed in the second stage. The choice of carbohydrate material depends upon its availability, and pretreatment is required before fermentation. We shall describe the bioprocess for the production of lactic acid from whey. 

Lactose is readily fermented by lactic acid bacteria, especially Lactococcus spp. and Lactobacillus spp., to lactic acid, and by some species of yeast, e.g. Kluyveromyces spp., to ethanol (Figure 2.27). Lactic acid may be used as a food acidulant, as a component in the manufacture of plastics, or converted to ammonium lactate as a source of nitrogen for animal nutrition. It can be converted to propionic acid, which has many food applications, by Propionibacterium spp. Potable ethanol is being produced commercially from lactose in whey or UF permeate. The ethanol may also be used for industrial purposes or as a fuel but is probably not cost-competitive with ethanol produced by fermentation of sucrose or chemically. The ethanol may also be oxidized to acetic acid. The mother liquor remaining from the production of lactic acid or ethanol may be subjected to anaerobic digestion with the production of methane (CH4) for use as a fuel several such plants are in commercial use. 

The production of substances that preserve the food from contamination or from oxidation is another important field of membrane bioreactor. For example, the production of high amounts of propionic acid, commonly used as antifungal substance, was carried out by a continuous stirred-tank reactor associated with ultrafiltration cell recycle and a nanofiltration membrane [51] or the production of gluconic acid by the use of glucose oxidase in a bioreactor using P E S membranes [52]. Lactic acid is widely used as an acidulant, flavor additive, and preservative in the food, pharmaceutical, leather, and textile industries. As an intermediate product in mammalian metabolism, L( +) lactic acid is more important in the food industry than the D(—) isomer. The performance of an improved fermentation system, that is, a membrane cell-recycle bioreactors MCRB was studied [53, 54], the maximum productivity of 31.5 g/Lh was recorded, 10 times greater than the counterpart of the batch-fed fermentation [54]. 

It may also be economical to remove the inhibitory product directly from the ongoing fermentation by extraction, membranes, or sorption. The use of sorption with simultaneous fermentation and separation for succinic acid has not been investigated. Separation has been used to enhance other organic acid fermentations through in situ separation or separation from a recycled side stream. Solid sorbents have been added directly to batch fermentations (18,19). Seevarantnam et al. (20) tested a sorbent in the solvent phase to enhance recovery of lactic acid from free cell batch culture. A sorption column was also used to remove lactate from a recycled side stream in a free-cell continuously stirred tank reactor (21). Continuous sorption for in situ separation in a biparticle fermentor was successful in enhancing the production of lactic acid (16,22). Recovery in this system was tested with hot water (16). 

Saha, B. C., and Nakamura, L. K. 2003. Production of mannitol and lactic acid by fermentation with Lactobacillus intermedius NRRL B-3693. Biotechnol. Bioeng., 82, 864-871. 

Soetaert, W., Buchholz, K., and Vandamme, E. J. 1995. Production of D-mannitol and D-lactic acid by fermentation with Leuconostoc mesenteroides. Agro. Food Ind. HiTech., 6, 41-44. 

Efficient lactic acid production from cane sugar molasses is achieved by Lactobacillus delbrueckii in batch fermentation. Fermentative production of lactic acid is very effective in producing optically pure l- or D-lactic and also DL-lactic acid, depending on the strain (Dumbrepatil et al., 2008). Lactobacillus plantarum cells are homofermentative, often used for production of lactic acid from glucose fermentation (Krishnan et al., 2001). 

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