Production of Lactic Acid

The L- isomer is produced in humans and other mammals, whereas both the D- and L-enantiomers are produced in bacterial systems. Lactic acid can also be derived chemically from renewable resources such as ethanol or acetaldehyde or from chemicals coming from coal (e.g. acetylene) or oil (e.g. ethylene) 

Figur 8.1 Stereoisomers of 2-hydroxypropionic acid (lactic acid). 

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Lactic acid and levulinic acid are two key intermediates prepared from carbohydrates [7]. Lipinsky [7] compared the properties of the lactide copolymers [130] obtained from lactic acid with those of polystyrene and polyvinyl chloride (see Scheme 4 and Table 5) and showed that the lactide polymer can effectively replace the synthetics if the cost of production of lactic acid is made viable. Poly(lactic acid) and poly(l-lactide) have been shown to be good candidates for biodegradeable biomaterials. Tsuji [131] and Kaspercejk [132] have recently reported studies concerning their microstructure and morphology. 

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. 

Lack of oxygen in blood or tissues. Tissue hypoxia can be caused by injury, inflammation, or tumor growth, due to disruption of blood supply. Tissue hypoxia is normally associated with acidosis, as anaerobic metabolism leads to production of lactic acid. 

A similar trend is also observed for the production of lactic acid in Fig.4. Maximum lactic acid concentration is attained for the 1mm bead diameter with a yield of 30.27 gL". A further increase in the bead diameter to 5mm results in a decrease of lactic acid production to 17.65 gL". Abdel-Naby et al. (1992) had studied the effect of bead diameter for lactic acid production and found the optimum lactic acid yield was obtained using a 2mm bead diameter. Lactic acid production increased as bead diameter continues to decrease. 

These new fermentation processes often require high costs for recovering the product from the fermentation broth. For instance, the production of lactic acid requires the neutralization of the product during the fermentation, to avoid acidification of the medium, and the subsequent re-acidification of the lactate [65]. Similarly, the recovery of 1-butanol implies the distillation of large amounts of water. Alternative recovery processes are therefore the subject of intensive research. 

Cyanide ion exerts an inhibitory action on certain metabolic enzyme systems, most notably cytochrome oxidase, the enzyme involved in the ultimate transfer of electrons to molecular oxygen. Because cytochrome oxidase is present in practically all cells that function under aerobic conditions, and because the cyanide ion diffuses easily to all parts of the body, cyanide quickly halts practically all cellular respiration. The venous blood of a patient dying of cyanide is bright red and resembles arterial blood because the tissues have not been able to utilize the oxygen brought to them. Cyanide intoxication produces lactic acidosis, the result of an increased rate of glycolysis and production of lactic acid. ... 

The action of alkaline reagents on sugars has been the subject of much study since Lobry de Bruyn s researches in 1896. Many complex changes are induced in the sugar molecule by alkaline reagents, as is exemplified by the researches of Evans.Here, however, mention will be made only of the production of lactic acid by the action of alkali on sucrose. 

Oxalic acid is poisonous to humans, but its concentrations are generally too low in foods to be of concern, although rhubarb leaves are quite poisonous. Lactic acid is produced from the fermentation of lactose, which is the principal sugar found in milk. The taste and smell of sour milk is due to the production of lactic acid from bacterial fermentation. Lactic acid accumulates in our muscles during exercise and strenuous physical activity. It is responsible for the sore, aching feeling often associated with these activities. Benzoic acid is the simplest aromatic carboxylic acid. 

Akerberg, C., Zacchi, G. (2000). An economic evaluation of the fermentative production of lactic acid from wheat flour. Bioresour. Technol., 75, 119-126. 

Zhang, Z. Y, Jin, B., Kelly, J. M. (2007). Production of lactic acid and byproducts from waste potato starch by Rhizopus arrhizus role of nitrogen sources. World J. Microbiol. BiotechnoL, 23,229-236. 

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 primary function of cheese starter cultures is to produce lactic acid at a predictable and dependable rate. The metabolism of lactose is summarized in Figure 10.12. Most cheese starters are homofermentative, i.e. produce only lactic acid, usually the L-isomer Leuconostoc species are heterofermentative. The products of lactic acid bacteria are summarized in Table 10.4. 

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). 

Lactamide has been prepared by the action of gaseous ammonia on ethyl lactate 3 and from lactic anhydride 4 and gaseous ammonia. It has been made also by the action of ammonia gas on lactide.5 The amide was obtained in excellent yields by treatment of the acetone condensation product of lactic acid with ammonia.6 Amides have been prepared by the reaction of liquid ammonia with esters at temperatures varying from — 330 to... 

Since lactose is absorbed slowly, a portion usually reaches the ileum, where it is utilized by bacterial flora, with the production of lactic acid. Lactose inhibits putrefaction by promoting the growth of aciduric bacteria in the intestine. 

Production of lactic acid using whey sometimes is industrially important. In this fermentation the culture of choice is L. bulgaricus because (1) it is homofermentative, producing almost theoretical yields of lactic acid (2) it is thermophilic and, having an optimum growth temperature between 45° and 50 °C, it can be grown in a pasteurized rather than a... 

Siebold, M., Frieling, V.P, Joppien, R., Rindfleisch, D., Schiigerl, K., and Roper, H. 1995. Comparison of the production of lactic acid by three different lactobacilli and its recovery by extraction... 

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). 

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