8- lactic acid

Lactic acid is one of the most widely distributed acids in nature and it is used to a great extent by the food industry. Its use in beverages, however, is limited. It has a mild taste relative to the other acids and is used in soft drinks as a flavour modifier or enhancer rather than as an acidulant. 

Lactic acid is supplied commercially as an odourless and colourless viscous liquid. It is produced via the fermentation, using lactic acid bacteria, of carbo-hydrates such as com, potato or rice starch, cane or beet sugar, or beet molasses. 

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). 

monocytogenes can utilize lactate as a carbohydrate source (Kouassi and Shelef, 1996). Stereospecific antimicrobial activity of lactic acid is not really applicable to L. monocytogenes. This also suggests considerable species-to-species variation in relative sensitivity to the two isomers, which may differentially influence the development of beneficial and unwanted bacteria, and in so doing, alter the composition of complex microflora. Clearer insight into the mechanisms involved could enhance the optimal use of lactic acid or lactic acid producers (Gravesen et al., 2004). 

Lactic acid is commonly found, which contributes to its wide use in food and food-related industries. It also has the potential for production of biodegradable and biocompatible polymers. These products have been proven to be environmentally friendly alternatives to biodegradable plastics derived from petrochemical materials (Zhang, Jin, and Kelly, 2007). Lactic acid is slightly lipid soluble and diffuses slowly through the cell membrane. As a result of this, the disruption of the cell pH is not its main mode of inhibition (Gravesen et al., 2004). 

Lactic acid is the major LAB metabolite, causing pH reductions that inhibit many microorganisms. However, both acetic and propionic acids have higher pKa values than lactic acid and, therefore, have a higher proportion of undissociated acid at a certain pH (Schniirer and Magnusson, 2005). 

Lactic acid occurs naturally in sour milk and in minor amounts in the muscle of animals, including humans. Commercially, lactic acid is produced by the fermentation of carbohydrates. 

This chapter is organized according to the nature and complexity of lactic acid itself and its derivatives. We begin by discussing the chemistry surrounding lactic acid and its esters. Then lactic acids with the hydroxyl function protected by a variety of removable groups are presented sequentially. A table of physical data associated with all the common protected lactic acid derivatives, discussed throughout this part of the book is presented at the end of the chapter. 

Commercial lactic acid has been determined to be a mixture of Ot-hydroxypropianic acid, lactyllactic acid, and water. When dilute lactic acid is concentrated, two molecules of lactic odd unite to form lactyllactic acid and water. The lactyllactic acid splits off from the woter. 

Polylactyllactic acids may also be formed by lass of water between the carboxyl and the olcohol groups, thus  

The conditions which affect the production af a lactic add solution from lactyllactic add are temperature, concentration and age af solution. 

A graph showing the Composition of Aqueous Lactic Acid Systems at Equilibrium and at Progress States of Dehydration. 

Naturally occurring lactic acid has the L-configuration. It accumulates under anaerobic conditions in a number of plants. L-Lactic acid is formed by reduction of pyruvate, which is an intermediary breakdown product of carbohydrate via the glycolysis pathway. 

Acid Family Genus and species Source References 

Chelidonic acid Hippocastanaceae Aesculus flava Leaves 98 

Keywords biodegradable, lactic acid (LA), poly (lactic acid) (PLA), syntiiesis, fermentation purification, crystallization, molecular distillation 

Lactic acid (chemically, 2-hydroxypropanoic acid, LA), also known as milk acid, is the most widely occurring carboxylic acid in nature. It was first isolated in 1780 by a Swedish chemist, Carl Wilhelm Scheele, but it was first produced commercially by Charles E. Avery at Littleton, Massachusetts, USA in 1881. 

Preparation and Properties of Lactic Acid (Section 298).—(a) In a 750-cc. flask dissolve 50 grams of cane-sugar or anhydrous glucose in 500 cc. of water add 20 cc. of sour milk and 20 grams of precipitated calcium carbonate. Set the flask in a warm place (temperature about 40°) and allow the fermentation to proceed for one week. The flask should be taken at least twice a day. At the end of the time add a small amount of calcium carbonate, heat to boiling, filter, pour the solution into a flat dish, and let it evaporate spontaneously. Filter off the solid by suction, dissolve it in a small amount of boiling water, filter 

—(a) The sour milk used in the preparation contains the lactic 

Department of Biotechnology, Graduate School of Engineering, Osaka University, Osaka, Japan 

5 Lactic Acid Production From Renewable Resources 

Bioprocessing of Renewable Resources to Commodity Bioproducts, First Edition. Edited by Virendra S. Bisaria and Akihiko Kondo. 

Lactic acid (LA), 2-hydroxypropionic acid, is the simplest hydroxyl acid. It has a long history, and it has existed from at least four to five thousand years ago for preservation of human foodstuffs by fermentation (Davidson et al., 1995). LA was first discovered in sour milk by Scheele in 1780, who initially considered it a milk component. In 1789, Lavoisier named this milk component acide lactique, which became the possible origin of the current terminology for LA. And later, Pasteur discovered that LA was not a milk component but a fermentation metabolite generated by certain microorganisms (Wee et al., 2006). In 1839, Fremy demonstrated fermentative production of LA from various kinds of carbohydrates such as sucrose, lactose, mannitol, starch, and dextrin. The first commercial production of LA started in the United States by a microbial process in 1881 (Vijayakumar et al., 2008). 

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A molecule is chiral if it cannot be superimposed on its mirror image (or if it does not possess an alternating axis of symmetry) and would exhibit optical activity, i.e. lead to the rotation of the plane of polarization of polarized light. Lactic acid, which has the structure (2 mirror images) shown exhibits molecular chirality. In this the central carbon atom is said to be chiral but strictly it is the environment which is chiral. 

CH3CH(0H)C(0)0Et. A colourless liquid with a pleasant odour, b.p. 154 C. Manufactured by distilling a mixture of ( )-lactic acid, ethanol and benzene in the presence of a little sulphuric or benzenesulphonic acid. It is a solvent for cellulose nitrate and acetate and also for various resins. Used as a lacquer solvent. 

C, b.p. 150 C/25mm. Prepared from l-lactic acid. It is partially converted to lactic acid by water. o-Lactide is similar. DL-Lactide crystallizes in colourless needles, m.p. 124-5 "C, b.p. l42°C/8mm. Obtained from DL-lactic acid. 

An example of a chiral compound is lactic acid. Two different forms of lactic acid that are mirror images of each other can be defined (Figure 2-69). These two different molecules are called enantiomers. They can be separated, isolated, and characterized experimentally. They are different chemical entities, and some of their properties arc different (c.g., their optical rotation),... 

Figure 2-69. The two enantiomers of lactic acid assignment of R and S configurations to the enantiomers of lactic acid after ranking the four ligands attached to the chiral center according to the Cl P rules (OH > COjH > Me > H).

Take two test-tubes A and B in A place about 5 ml. of neutralised tartaric acid solution and in B place 5 ml. of distilled water. To each solution add 3-4 drops of ferric chloride solution. Place a piece of white paper under the tubes, look down their length and note that A is definitely yellow compared with the control tube B. This yellow colour is given by a-hydroxy-carboxylic-acids, lactic acid, tartaric acid, citric acid. 

Physical properties. All are colourless crystalline solids except formic acid, acetic acid (m.p. 18 when glacial) and lactic acid (m.p. 18°, usually a syrup). Formic acid (b.p. loo ") and acetic acid (b.p. 118 ) are the only members which are readily volatile lactic acid can be distilled only under reduced pressure. Formic and acetic acids have characteristic pungent odours cinnamic acid has a faint, pleasant and characteristic odour. 

Iodoform reaction. To 0 5 ml. of lactic acid add 10% NaOH solution until alkaline to litmus. Then add 5 ml. of 10% KI solution and 10 ml. of freshly prepared sodium hypochlorite solution and mix well. A yellow precipitate of iodoform separates out almost immediately in the cold. 

Lactic acid iso-Propyl alcohol tso-Propyl lactate... 

Lactic acid tends to pass into the lactide I [ when heated in... 

Place a mixture of 53 g. of A.R. lactic acid (85-88 per cent, acid), 75 g. (85-5 ml.) of commercial anhydrous isopropyl alcohol, 300 ml. of benzene and 20 g. of Zeo-Karb 225/H (1) in a 700 ml. bolt-head flask, equipped with an automatic water separator (e.g., a large modified Dean and Stark apparatus with a stopcock at the lower end, see Fig. Ill, 126, 1) carrying an efficient reflux condenser at its upper end, and a mercury-sealed stirrer (alternatively, the hquid-sealed stirrer shown in Fig. 11,7,11, c. may be used). Reflux the mixture, with stirring, on a steam bath for 5 hours or until water no longer collects in appreciable amount in the water separator run off the water from time to time. Filter off the resin at the pump and wash it with two 25 ml. portions of benzene. Shake the combined filtrate and washings with about 5 g. of precipit-ated calcium... 

Supplement (combined with Volume IV) III, 2nd 1929 195-449 Hydroxy-carboxylic acids Carbonic acid, 3. GlycoUic acid, 228. Lactic acid, 261. Tartaric acid, 481. Citric acid, 556. Urea, 42. Cyanamide, 74. Thiocyemic acid, 140. 

Caustic alkalis. Dilute by drinking much water, followed by vinegar, lemon or orange juice, or solutions of lactic acid or citric acid. Milk may then be given but no emetics. 

Specific rotation is a physical property of a substance just as melting point boil mg point density and solubility are For example the lactic acid obtained from milk is exclusively a single enantiomer We cite its specific rotation m the form [a]o =+3 8° The temperature m degrees Celsius and the wavelength of light at which the measure ment was made are indicated as superscripts and subscripts respectively... 

IS the oxidation of lactic acid to pyruvic acid by NAD and the enzyme lactic acid coenzyme NAD ... 

Enzyme catalyzed reductions of carbonyl groups are more often than not com pletely stereoselective Pyruvic acid for example is converted exclusively to (5) (+) lactic acid by the lactate dehydrogenase NADH system (Section 15 11) The enantiomer... 

The enzyme is a single enantiomer of a chiral molecule and binds the coenzyme and substrate m such a way that hydride is transferred exclusively to the face of the carbonyl group that leads to (5) (+) lactic acid Reduction of pyruvic acid m the absence of an enzyme however say with sodium borohydride also gives lactic acid but as a racemic mixture containing equal quantities of the R and S enantiomers... 

Formic acid Acetic acid Stearic acid Lactic acid... 

This difference in behavior for acetic acid in pure water versus water buffered at pH = 7 0 has some important practical consequences Biochemists usually do not talk about acetic acid (or lactic acid or salicylic acid etc) They talk about acetate (and lac tate and salicylate) Why Its because biochemists are concerned with carboxylic acids as they exist in di lute aqueous solution at what is called biological pH Biological fluids are naturally buffered The pH of blood for example is maintained at 7 2 and at this pH carboxylic acids are almost entirely converted to their carboxylate anions... 

In spite of the number of different structural types lipids share a common biosyn thetic origin m that they are ultimately derived from glucose During one stage of car bohydrate metabolism called glycolysis glucose is converted to lactic acid Pyruvic acid IS an intermediate... 

Chiral Center. The chiral center, which is the chiral element most commonly met, is exemplified by an asymmetric carbon with a tetrahedral arrangement of ligands about the carbon. The ligands comprise four different atoms or groups. One ligand may be a lone pair of electrons another, a phantom atom of atomic number zero. This situation is encountered in sulfoxides or with a nitrogen atom. Lactic acid is an example of a molecule with an asymmetric (chiral) carbon. (See Fig. 1.13b.)... 

FIGURE 1.13 Asymmetric (chiral) carbon in the lactic acid molecule. 

A simpler representation of molecules containing asymmetric carbon atoms is the Fischer projection, which is shown here for the same lactic acid configurations. A Fischer projection involves... 

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