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Biotechnological Production of Lactic Acid and
Its Recent Applications
Young-Jung Wee1, Jin-Nam Kim2and Hwa-Won Ryu1*
1School of Biological Sciences and Technology, Chonnam National University, Gwangju 500-757,
Republic of Korea
2Department of Material Chemical and Biochemical Engineering, Chonnam National University,
Gwangju 500-757, Republic of Korea
Received: December 3, 2005
Accepted: March 12, 2006
Summary
Lactic acid is widely used in the food, cosmetic, pharmaceutical, and chemical indus-
tries and has received increased attention for use as a monomer for the production of bio-
degradable poly(lactic acid). It can be produced by either biotechnological fermentation or
chemical synthesis, but the former route has received considerable interest recently, due to
environmental concerns and the limited nature of petrochemical feedstocks. There have
been various attempts to produce lactic acid efficiently from inexpensive raw materials.
We present a review of lactic acid-producing microorganisms, raw materials for lactic acid
production, fermentation approaches for lactic acid production, and various applications
of lactic acid, with a particular focus on recent investigations. In addition, the future po-
tentials and economic impacts of lactic acid are discussed.
Key words: lactic acid, poly(lactic acid), lactic acid bacteria, fermentation, biodegradable
polymer
Introduction
Lactic acid has a long history of uses for fermenta-
tion and preservation of human foodstuffs (1). It was
first discovered in sour milk by Scheele in 1780, who ini-
tially considered it a milk component. In 1789, Lavoisier
named this milk component »acide lactique«, which be-
came the possible origin of the current terminology for
lactic acid. In 1857, however, Pasteur discovered that it
was not a milk component, but a fermentation metabo-
lite generated by certain microorganisms (2).
Lactic acid can be produced by either microbial fer-
mentation or chemical synthesis (Fig. 1). In the early 1960s,
a method to synthesize lactic acid chemically was devel-
oped due to the need for heat-stable lactic acid in the
baking industry (3). There are two optical isomers of lac-
tic acid: L(+)-lactic acid and D(–)-lactic acid. Lactic acid
is classified as GRAS (generally recognized as safe) for
use as a food additive by the US FDA (Food and Drug
Administration), but D(–)-lactic acid is at times harmful to
human metabolism and can result in acidosis and decal-
cification (4). Although racemic DL-lactic acid is always
produced by chemical synthesis from petrochemical re-
sources, an optically pure L(+)- or D(–)-lactic acid can be
obtained by microbial fermentation of renewable resources
when the appropriate microorganism that can produce
only one of the isomers is selected (5). The optical purity
of lactic acid is crucial to the physical properties of poly
(lactic acid) (PLA), and an optically pure L(+)- or D(–)-lac-
tic acid, rather than racemic DL-lactic acid, can be poly-
merized to a high crystalline PLA that is suitable for com-
mercial uses (6,7). Therefore, the biotechnological pro-
duction of lactic acid has received a significant amount
of interest recently, since it offers an alternative to envi-
ronmental pollution caused by the petrochemical indus-
try and the limited supply of petrochemical resources.
*Corresponding author; Phone: ++82 62 53 01 842; Fax: ++82 62 53 01 909; E-mail: hwryu@chonnam.ac.kr
Lactic acid is now considered to be one of the most
useful chemicals, used in the food industry as a preser-
vative, acidulant, and flavouring, in the textile and phar-
maceutical industries, and in the chemical industry as a
raw material for the production of lactate ester, propyl-
ene glycol, 2,3-pentanedione, propanoic acid, acrylic acid,
acetaldehyde, and dilactide (8,9). Recently, lactic acid
consumption has increased considerably because of its
role as a monomer in the production of biodegradable
PLA, which is well-known as a sustainable bioplastic
material (4,10). The worldwide demand for lactic acid is
estimated roughly to be 130 000 to 150 000 (metric) tonnes
per year (11). However, the global consumption of lactic
acid is expected to increase rapidly in the near future.
NatureWorks LLC, a major PLA manufacturer estab-
lished in the US, expects that the global PLA market
may increase to 500 000 (metric) tonnes per year by 2010
(12).
Biotechnological processes for the production of lac-
tic acid usually include lactic acid fermentation and
product recovery and/or purification. There have been
numerous investigations on the development of biotech-
nological processes for lactic acid production, with the
ultimate objectives to enable the process to be more effi-
cient and economical. This article presents a review of
recent advances in the biotechnological production of
lactic acid, as well as its recent applications and the fu-
ture prospects of biologically-derived lactic acid.
Lactic Acid-Producing Microorganisms
Microorganisms that can produce lactic acid can be
divided into two groups: bacteria and fungi (10). The
microorganisms selected for recent investigations of the
biotechnological production of lactic acid are listed in
Table 1 (13–24). Although most investigations of lactic
acid production were carried out with lactic acid bacte-
ria (LAB), filamentous fungi, such as Rhizopus, utilize
glucose aerobically to produce lactic acid (13,25,26). Rhi-
zopus species such as R. oryzae and R. arrhizus have amy-
lolytic enzyme activity, which enables them to convert
starch directly to L(+)-lactic acid (27,28). Fungal fermen-
tation has some advantages in that R. oryzae requires
only a simple medium and produces L(+)-lactic acid, but
it also requires vigorous aeration because R. oryzae is an
obligate aerobe (25). In fungal fermentation, the low pro-
duction rate, below 3 g/(L·h), is probably due to the low
reaction rate caused by mass transfer limitation (14). The
lower product yield from fungal fermentation is attrib-
uted partially to the formation of by-products, such as
fumaric acid and ethanol (25).
Fig. 1. Overview of the two manufacturing methods of lactic acid; chemical synthesis (a) and microbial fermentation (b). SSF repre-
sents simultaneous saccharification and fermentation
Table 1. Microorganisms used for recent investigations of the biotechnological production of lactic acid
Organism g(lactic acid)
g/L
h(yield)
g/g
Productivity
g/(L·h) Reference
Rhizopus oryzae ATCC 52311 83.0 0.88 2.6 (13)
Rhizopus oryzae NRRL 395 104.6 0.87 1.8 (14)
Enterococcus faecalis RKY1 144.0 0.96 5.1 (15)
Lactobacillus rhamnosus ATCC 10863 67.0 0.84 2.5 (16)
Lactobacillus helveticus ATCC 15009 65.5 0.66 2.7 (17)
Lactobacillus bulgaricus NRRL B-548 38.7 0.90 3.5 (18)
Lactobacillus casei NRRL B-441 82.0 0.91 5.6 (19)
Lactobacillus plantarum ATCC 21028 41.0 0.97 1.0 (20)
Lactobacillus pentosus ATCC 8041 21.8 0.77 0.8 (21)
Lactobacillus amylophilus GV6 76.2 0.70 0.8 (22)
Lactobacillus delbrueckii NCIMB 8130 90.0 0.97 3.8 (23)
Lactococcus lactis ssp. lactis IFO 12007 90.0 0.76 1.6 (24)
Several attempts have been made to achieve higher
cell density, lactic acid yield, and productivity in fungal
fermentation. Tay and Yang (25) immobilized R. oryzae
cells in a fibrous bed to produce lactic acid from glucose
and starch. Kosakai et al. (26) cultured R. oryzae cells with
the use of mycelial flocs formed by the addition of min-
eral support and poly(ethylene oxide). They observed
that cotton-like mycelial flocs were the optimal morpho-
logy in the culture of R. oryzae. Park et al. (14) reported
that lactic acid production was enhanced in a culture of
R. oryzae, by the induction of mycelial floc morphology.
Their results also suggested that cotton-like mycelial flocs
were the optimal morphology for use in the air-lift bio-
reactor culture of R. oryzae. Although there have been
persistent attempts to produce lactic acid through fun-
gal fermentation, LAB have been commonly used for
the production of lactic acid due to the aforementioned
disadvantages of fungal fermentation.
Lactic acid bacteria can be classified into two groups:
homofermentative and heterofermentative. While the ho-
mofermentative LAB convert glucose almost exclusively
into lactic acid, the heterofermentative LAB catabolize
glucose into ethanol and CO2as well as lactic acid (Fig.
2) (5,29). The homofermentative LAB usually metabolize
glucose via the Embden-Meyerhof pathway (i.e. glyco-
lysis). Since glycolysis results only in lactic acid as a ma-
jor end-product of glucose metabolism, two lactic acid
molecules are produced from each molecule of glucose
with a yield of more than 0.90 g/g (30,31). Only the ho-
mofermentative LAB are available for the commercial pro-
duction of lactic acid (5,15).
Recently, strains used in the commercial production
of lactic acid has become almost proprietary, and it is
believed that most of the LAB used belong to the genus
Lactobacillus (4,5). Berry et al. (16) attempted to produce
lactic acid by batch culture of L. rhamnosus in a defined
medium. Schepers et al. (17) used L. helveticus for the
production of lactic acid from lactose and concentrated
cheese whey, and Burgos-Rubio et al. (18) reported the
kinetic investigation of the conversion of different sub-
strates into lactic acid with the use of L. bulgaricus.Hu
-
janen and Linko (19) investigated the effects of culture
temperature and nitrogen sources on lactic acid produc-
tion by L. casei, and Roukas and Kotzekidou (32) also
used this strain for lactic acid production from deprote-
inized whey by mixed cultures of free and coimmobili-
zed cells. Fu and Mathews (20) investigated the kinetic
model of lactic acid production from lactose by batch
culture of L. plantarum, and Bustos et al. (21) used L. pen-
tosus for the production of lactic acid from vine-trim-
ming wastes. The strains of amylase-producing L. amylo-
philus were used often for the direct conversion of starch
into lactic acid (22,33,34).
However, among the genus Lactobacillus,L. delbru-
eckii has appeared commonly in many investigations on
the production of lactic acid. Kotzanmanidis et al. (23)
used L. delbrueckii NCIMB 8130 for lactic acid production
from beet molasses. Monteagudo et al. (35) and Göksun-
gur and Güvenç (36) also attempted to produce lactic
acid from beet molasses with L. delbrueckii. In addition
to lactobacilli, strains of lactococci were often used for
lactic acid production. Roble et al. (24) co-cultured Lacto-
coccus lactis ssp. lactis cells with Aspergillus awamori for
lactic acid production from cassava starch, and Åkerberg
et al. (37) used L. lactis ssp. lactis for modeling the kinet-
ics of lactic acid production from whole wheat flour.
Moreover, Yun et al. (15) and Wee et al. (38) reported the
production of lactic acid by batch culture of a newly iso-
lated species, Enterococcus faecalis.
Efforts have been made to improve the production
of lactic acid through metabolic engineering approaches.
Kylä-Nikkilä et al. (39) attempted to express L-lactate de-
Fig. 2. Metabolic pathways of homofermentative (solid line) and heterofermentative (dotted line) lactic acid bacteria: P, phosphate;
ADP, adenosine 5'-diphosphate; ATP, adenosine 5'-triphosphate; NAD+, nicotinamide adenine dinucleotide; NADH, nicotinamide
adenine dinucleotide (reduced form); (1), lactate dehydrogenase; (2), alcohol dehydrogenase
hydrogenase and D-lactate dehydrogenase genes in L.
helveticus for the production of pure D(–)- and L(+)-lactic
acids. They constructed two D-lactate dehydrogenase gene-
-negative L. helveticus via a gene replacement method for
the production of pure L-lactic acid. Each L-lactate dehy-
drogenase activity of two D-lactate dehydrogenase-defi-
cient L. helveticus was 53 or 93 % higher than that of the
wild type strain. Dien et al. (40,41) constructed recombi-
nant Escherichia coli for the conversion of hexose sugar,
as well as pentose sugar, into L(+)-lactic acid, and they
metabolically engineered the E. coli for the construction
of carbon catabolite repression mutants. Similarly, Chang
et al. (42) constructed recombinant E. coli for the produc-
tion of optically pure D(–)- or L(+)-lactic acid. They in-
troduced L-lactate dehydrogenase genes from L. casei into
apta ldhA strain, which lacked phosphotransacetylase and
D-lactate dehydrogenase. Their results suggested that the
central fermentation metabolism of E. coli can be reori-
ented to the production of D(–)- or L(+)-lactic acid. Re-
cent advances in metabolic engineering of microorgan-
isms may provide more opportunities for selective and
efficient production of optically pure lactic acid through
the improvement of future strains.
Lactic acid bacteria typically have complex nutritio-
nal requirements, due to their limited ability to synthe-
size their own growth factors such as B vitamins and
amino acids. They require some elements for growth, such
as carbon and nitrogen sources, in the form of carbohy-
drates, amino acids, vitamins, and minerals (29,43,44).
There are several growth-stimulation factors that have a
considerable effect on the production rate of lactic acid.
The mixture of amino acids, peptides, and amino acid
amides usually stimulates the growth of LAB, and the
resulting growth rates are much higher than those ob-
tained with free amino acids (43). Fatty acids also influ-
ence LAB growth, and phosphates are the most impor-
tant salt in lactic acid fermentation. Ammonium ions
cannot serve as the sole nitrogen source, but they seem
to have some influence on the metabolism of certain
amino acids. Since minerals do not seem to be essential
to LAB growth, the amount found in commercial com-
plex media is usually sufficient (29,45). Temperature and
pH are also important factors influencing LAB growth
and lactic acid production (5). In general, the desirable
characteristics for industrial LAB are the abilities to rap-
idly and completely convert cheap raw materials into
lactic acid with minimal nutritional requirements and to
provide high yields of preferred stereoisomer without
by-product formation.
Raw Materials for Biotechnological
Production of Lactic Acid
In order for the biotechnological production of lactic
acid to be feasible, cheap raw materials are necessary,
because polymer producers and other industrial users
usually require large quantities of lactic acid at a rela-
tively low cost. Raw materials for lactic acid production
should have the following characteristics: cheap, low le-
vels of contaminants, rapid production rate, high yield,
little or no by-product formation, ability to be fermented
with little or no pre-treatment, and year-round availabil-
ity (3). When refined materials are used for production,
the costs for product purification should be significantly
reduced. However, this is still economically unfavour-
able because the refined carbohydrates are so expensive
that they eventually result in higher production costs
(5). Therefore, there have been many attempts to screen
for cheap raw materials for the economical production
of lactic acid. Reports in the literature of recent investi-
gations are listed in Table 2 (23,38,46–61).
Table 2. Reports in the literature about recent investigations on the biotechnological production of lactic acid from cheap raw materials
Raw material Organism g(lactic acid)
g/L
Productivity
g/(L·h) Reference
Molasses Lactobacillus delbrueckii NCIMB 8130 90.0 3.8 (23)
Enterococcus faecalis RKY1 95.7 4.0 (38)
Rye Lactobacillus paracasei No. 8 84.5 2.4 (46)
Sweet sorghum Lactobacillus paracasei No. 8 81.5 2.7 (46)
Lactobacillus paracasei No. 8 106.0 3.5 (47)
Wheat Lactococcus lactis ssp. lactis ATCC 19435 106.0 1.0 (48)
Enterococcus faecalis RKY1 102.0 4.8 (49)
Corn Enterococcus faecalis RKY1 63.5 0.5 (49)
Lactobacillus amylovorus ATCC 33620 10.1 0.8 (50)
Cassava Lactobacillus amylovorus ATCC 33620 4.8 0.2 (50)
Potato Lactobacillus amylovorus ATCC 33620 4.2 0.1 (51)
Rice Lactobacillus sp. RKY2 129.0 2.9 (51)
Barley Lactobacillus casei NRRL B-441 162.0 3.4 (52)
Lactobacillus amylophilus GV6 27.3 0.3 (53)
Cellulose Lactobacillus coryniformis ssp. torquens ATCC 25600 24.0 0.5 (54)
Corncob Rhizopus sp. MK-96-1196 24.0 0.3 (55)
Waste paper Lactobacillus coryniformis ssp. torquens ATCC 25600 23.1 0.5 (56)
Rhizopus oryzae NRRL 395 49.1 0.7 (57)
Wood Lactobacillus delbrueckii NRRL B-445 108.0 0.9 (58)
Enterococcus faecalis RKY1 93.0 1.7 (59)
Whey Lactobacillus helveticus R211 66.0 1.4 (60)
Lactobacillus casei NRRL B-441 46.0 4.0 (61)
Cheap raw materials, such as starchy and cellulosic
materials, whey, and molasses, have been used for lactic
acid production (5). Among these, starchy and cellulosic
materials are currently receiving a great deal of atten-
tion, because they are cheap, abundant, and renewable
(9,46,62). The starchy materials used for lactic acid pro-
duction include sweet sorghum (46,47), wheat (9,37,48,
49), corn (49,50), cassava (50), potato (50,63), rice (49,51),
rye (46), and barley (49,52,53). These materials have to
be hydrolyzed into fermentable sugars before fermenta-
tion, because they consist mainly of a(1,4)- and a(1,6)-link-
ed glucose (47–49). This hydrolysis can be carried out si-
multaneously with fermentation (52). Amylase-produc-
ing L. amylophilus and L. amylovorus are often used for
the direct fermentation of starchy materials into lactic
acid (50,53,63).
Cellulosic materials have been used for lactic acid
production in similar ways as starchy materials (5). These
materials consist mainly of b(1,4)-glucan, and often con-
tain xylan, arabinan, galactan, and lignin (5,10). Venka-
tesh (62) and Yáñez et al. (54) have previously attempted
to produce lactic acid from pure cellulose through si-
multaneous saccharification and fermentation (SSF). The
utilization of corncob (55,64), waste paper (56,57), and
wood (58,59), has been reported as well. Sreenath et al.
(65) investigated the production of lactic acid from agri-
cultural residues such as alfalfa fiber, wheat bran, corn
stover, and wheat straw. They suggested that, during
SSF of alfalfa fiber, lactic acid production was enhanced
by adding pectinase and cellulase together. Garde et al.
(66) used hemicellulose hydrolyzate from wheat straw
for lactic acid production by co-culture of L. brevis and
L. pentosus. This study demonstrated that complete sub-
strate utilization was achieved with a mixed culture of
two LAB. Fermentation of lignocellulosic hydrolyzate is
inhibited usually by inhibitory compounds, such as fur-
fural, 5-hydroxymethyl furfural, and acetic acid, which
are generated during pre-treatment of lignocellulose (67).
Most studies on methods to decrease this inhibition have
been focused on the chemical and physical detoxifica-
tion of the hydrolyzate (68). Wee et al. (59), however,
reported that the inhibition of fermentation caused by
wood hydrolyzate was reduced to a slight degree by di-
rect adaptation of LAB to the wood hydrolyzate-based
medium.
Some industrial waste products, such as whey and
molasses, are of interest for common substrates for lactic
acid production. Whey is a major by-product of the dai-
ry industry, and it contains lactose, protein, fat, and mi-
neral salts. For complete utilization of whey lactose, it is
necessary to supplement whey with an additional nitro-
gen source (5). Amrane and Prigent (69), Kulozik and
Wilde (70), and Schepers et al. (60) supplemented whey
with yeast extract for rapid production of lactic acid with
L. helveticus. According to Fitzpatrick and O’Keeffe (71),
the addition of whey protein hydrolyzate to whey me-
dium would make the fermentation more economically
viable and would also reduce the amount of unused nu-
trients left during fermentation. Also, there have been
several attempts to produce lactic acid from whey by
batch culture of L. casei (61,72,73). Molasses is a waste
product from the sugar manufacturing process, and it
usually contains a large amount of sucrose (5). L. delbru-
eckii and E. faecalis have recently been used for lactic acid
production from molasses (23,35,36,38). Shukla et al. (74)
also reported D(–)-lactic acid production from molasses
with recombinant E. coli strain.
It is necessary to supplement the fermentation media
with sufficient nutrients for rapid lactic acid production.
The most common nutrient for lactic acid production is
yeast extract, but this may contribute significantly to an
increase in production costs (3,5). As an alternative to
yeast extract, corn steep liquor, a by-product from the
corn steeping process, has been used successfully for lac-
tic acid production (49). The nitrogen content of corn steep
liquor is dependent on the steeping process used. Since
it is derived from corn, 85 % of its total nitrogen content
is composed of proteins, peptides, and amino acids (75).
Yun et al. (51) suggested that rice bran and wheat bran
play important roles as effective nutrients for lactic acid
production, because they usually contain several nutri-
tional factors as well as fermentable carbohydrates. Kur-
banoglu and Kurbanoglu (76) demonstrated that ram
horn waste was an effective supplement for lactic acid
production. Similarly, Bustos et al. (77) proposed that
vinification lees could be used for the formulation of
low-cost media for lactic acid production. According to
Wee et al. (78), wastewater from electrodialyzed fermen-
tation broth still contained some nutrients that could be
available to LAB. Their result indicated that, if small
amounts of other nutrients were supplemented to elec-
trodialysis wastewater, then the efficiencies of fermenta-
tion would be improved significantly.
Fermentation Approaches to Lactic
Acid Production
Batch, fed-batch, repeated batch, and continuous
fermentations are the most frequently used methods for
lactic acid production. Higher lactic acid concentrations
may be obtained in batch and fed-batch cultures than in
continuous cultures, whereas higher productivity may be
achieved by the use of continuous cultures (5). Another
advantage of the continuous culture compared to the
batch culture, is the possibility to continue the process
for a longer period of time. Reports in the literature of
recent studies on the biotechnological production of lac-
tic acid by different fermentation approaches are listed
in Table 3 (32,79–86).
The cell-recycle system, together with repeated batch
and continuous processes, enables the achievement of a
higher cell concentration and product productivity in
the process (79,80). Oh et al. (79) produced lactic acid at
a rate of 6.4 g/(L·h) through cell-recycle repeated batch
fermentation. Their results also indicated that only 26 %
of the yeast extract dosage, compared with conventional
batch fermentation, should be required to produce the
same amount of lactic acid, which might result in a con-
siderable reduction of production costs. The maximum
cell concentration in their experiment was greater than
28 g/L, which might contribute to the improvement of
the productivity and reduction of nutrient supplemen-
tation. A successful approach to continuous production
of lactic acid with cell retention has been reported by
Kwon et al. (80), who recently attempted to produce lac-
tic acid by a two-stage cell-recycle culture of L. rhamno-
sus. They connected the membrane cell-recycle bioreac-
tors in a series, and obtained 92 g/L of lactic acid with a
productivity of 57 g/(L·h).
Immobilization of cells has been one of the means
for high cell retention in the bioreactor (87). Several ma-
terials, such as Ca-alginate gels, poly(ethyleneimine), and
plastic composite support, have been used for immobili-
zation of LAB in order to produce lactic acid (36,81,87).
Senthuran et al. (87) reported the production of lactic acid
by continuous culture of L. casei immobilized in poly(ethy-
leneimine). This system was coupled with a cell-recycle
bioreactor, and the authors observed that the most im-
portant factor for operational stability was the bead size
of the matrix. Cotton et al. (81) tested the immobilized-
-cell biofilm reactor for continuous production of lactic
acid. For biofilm formation, they used a plastic compos-
ite support composed mainly of polypropylene.
Lactic acid production processes traditionally suffer
from end-product inhibition. An undissociated lactic acid
passes through the bacterial membrane and dissociates
inside the cell. The inhibition mechanism of lactic acid is
probably related to the solubility of the undissociated lac-
tic acid within the cytoplasmic membrane and the insol-
ubility of dissociated lactate, which causes acidification
of cytoplasm and failure of proton motive forces. It even-
tually influences the transmembrane pH gradient and
decreases the amount of energy available for cell growth
(29,88). Therefore, to alleviate the inhibitory effect of lac-
tic acid during the fermentation, it must be removed se-
lectively in situ from the fermentation broth.
Recently, various attempts have been carried out to
remove the lactic acid simultaneously as it is formed.
Hano et al. (89) studied the reactive extraction of lactic
acid from the fermented broth. They indicated that in
situ extraction was possible with the use of di-n-octyl-
amine and with adjustment of the fermentation broth to
a pH=5.0 by ammonia. Iyer and Lee (82) attempted to
extract lactic acid simultaneously with the use of a two-
-zone fermentor-extractor system. The system was opera-
ted under a fed-batch mode with in situ removal of lactic
acid by solvent extraction. Electrodialysis fermentation
with ion exchange membranes was often used for in situ
removal of lactic acid (83,90). Min-Tian et al. (84) had
previously developed a continuous electrodialysis fermen-
tation system for the production of lactic acid. In their
study, the system of electrodialysis fermentation with a
level meter was the most efficient system and a higher
yield could be obtained if the glucose concentration in
the broth could be controlled to remain at a lower level.
Nanofiltration membranes and ion exchange resins were
occasionally coupled with the bioreactor for in situ re-
moval of lactic acid (85,86).
Current Uses and Applications of Lactic Acid
Lactic acid has received a significant amount of at-
tention as a chemical with many potential applications.
There are four major categories for the current uses and
applications of lactic acid: food, cosmetic, pharmaceutical,
and chemical applications. The potential applications of
lactic acid are illustrated in Fig. 3. Since lactic acid is
classified as GRAS for use as a food additive by the US
FDA (4), it is widely used in almost every segment of
the food industry, where it serves in a wide range of
functions, such as flavouring, pH regulation, improved
microbial quality, and mineral fortification. Moreover,
lactic acid is used commercially in the processed meat
and poultry industries, to provide products with an in-
creased shelf life, enhanced flavour, and better control
of food-born pathogens. Due to the mild acidic taste of
lactic acid, it is also used as an acidulant in salads and
dressings, baked goods, pickled vegetables, and bever-
ages. Lactic acid is used in confectionery, not only for
flavour, but also to bring the pH of the cooked mix to
the correct point for setting. The advantages of adding
lactic acid in confectionery include its low inversion
rate, ease of handling, and ability to produce clear can-
dies. Another potential application of lactic acid in the
food industry is the mineral fortification of food prod-
ucts (91,92).
Lactic acid offers natural ingredients for cosmetic ap-
plications. Although primarily used as moisturizers and
pH regulators, they possess multiple other properties
such as antimicrobial activity, skin lightening, and skin
Table 3. Reports in the literature of recent investigations on the biotechnological production of lactic acid by different fermentation
approaches
Organism Fermentation mode g(lactic acid)
g/L
Productivity
g/(L·h) Reference
Lactobacillus casei SU No 22 +
Lactobacillus lactis WS 1042
fed-batch, coimmobilization 47.0 2.0 (32)
Enterococcus faecalis RKY1 batch 95.7 4.0 (79)
repeated batch, cell-recycle via membrane 93.2 6.4 (79)
Lactobacillus rhamnosus ATCC 10863 batch ~120.0 2.1 (80)
continuous, cell-recycle via membrane 92.0 57.0 (80)
Lactobacillus casei ssp. rhamnosus ATCC 11443 continuous, cell-recycle via immobilization 22.4 9.0 (81)
Lactobacillus delbrueckii NRRL B445 fed-batch, in situ removal via solvent extraction ~23.1 0.2 (82)
Lactococcus lactis IO-1 JCM 7638 batch, in situ removal via electrodialysis ~39.0 0.9 (83)
Lactobacillus rhamnosus IFO 3863 batch 98.0 1.9 (84)
continuous, in situ removal via electrodialysis ~20.0 8.2 (84)
Lactobacillus helveticus CNRZ 303 continuous, cell-recycle via membrane 55.0 7.1 (85)
Lactobacillus delbrueckii CECT 286 continuous, in situ removal via ion-exchange resin 26.1 10.4 (86)
hydration. The moisturizing effect is related directly to
lactate’s water retaining capacity, and the skin-lighten-
ing action of lactic acid is produced by the suppression
of the formation of tyrosinase. Since they are natural in-
gredients of the human body, lactic acid and its salt fit
perfectly into the modern trend towards natural and sa-
fer formulations, and they produce such effects as skin
lightening and rejuvenation, which makes them very use-
ful as active ingredients in cosmetics (91,92).
Lactic acid is also used in the pharmaceutical indus-
try as an electrolyte in many parenteral/I.V. (intravenous)
solutions that are intended to replenish the bodily fluids
or electrolytes. Examples include Lactated Ringer’s or
Hartmann’s solutions, CAPD (continuous ambulatory pe-
ritoneal dialysis) solution, and dialysis solution for con-
ventional artificial kidney machines. Moreover, lactic acid
is used in a wide variety of mineral preparations, which
include tablets, prostheses, surgical sutures, and con-
trolled drug delivery systems (91,92).
Lactic acid and its salt are used increasingly in vari-
ous types of chemical products and processes. In this ca-
tegory of applications, lactic acid functions as a descal-
ing agent, pH regulator, neutralizer, chiral intermediate,
solvent, cleaning agent, slow acid-release agent, metal
complexing agent, antimicrobial agent, and humectant.
Natural lactic acid has an emerging use as an excellent
and safe solvent, which is alternative in many fine me-
chanical cleaning applications. Due to the high solvency
power and solubility of lactic acid, it is an excellent
remover of polymer and resins. It is available with an
isomeric purity greater than 98 %, and is suitable as a
starting material in the production of herbicides or
pharmaceuticals. Since lactic acid offers better descaling
properties than conventional organic descalers do, it is
often used in many decalcification products, such as
bathroom cleaners, coffee machines, and toilets. Ethyl
lactate is used in many anti-acne preparations, because
it combines excellent solvency power against oils and
polymeric stains, with no environmental impact and to-
xicological effects (4,91,92).
Currently, lactic acid is considered the most poten-
tial feedstock monomer for chemical conversions, be-
cause it contains two reactive functional groups, a car-
boxylic group and a hydroxyl group. Lactic acid can
undergo a variety of chemical conversions into poten-
tially useful chemicals, such as propylene oxide (via hy-
drogenation), acetaldehyde (via decarboxylation), acrylic
acid (via dehydration), propanoic acid (via reduction),
2,3-pentanedione (via condensation), and dilactide (via
self-esterification) (8). Lactic acid has recently received a
great deal of attention as a feedstock monomer for the
production of PLA, which serves as a biodegradable
commodity plastic. The optically pure lactic acid can be
polymerized into a high molecular mass PLA through
the serial reactions of polycondensation, depolymeriza-
tion, and ring-opening polymerization (7). The resultant
polymer, PLA, has numerous uses in a wide range of
applications, such as protective clothing, food packag-
ing, mulch film, trash bags, rigid containers, shrink wrap,
and short shelf-life trays (93,94). The recent huge growth
of the PLA market will stimulate future demands on
lactic acid considerably (4,6).
Conclusions and Future Potentials
The current major markets for lactic acid are food-
-related industries, but the emerging markets for PLA
polymer would cause a significant increase in growth of
lactic acid consumption (4,10). Currently, the worldwide
consumption of lactic acid is estimated to be 130 000–
–150 000 (metric) tonnes per year, and the commercial pri-
ces of food grade lactic acid range between 1.38 US$/kg
Fig. 3. Diagram of the commercial uses and applications of lactic acid and its salt
(for 50 % purity) and 1.54 US$/kg (for 88 % purity). Tech-
nical grade lactic acid with 88 % purity has been priced
as much as 1.59 US$/kg (11,95). Lactic acid consump-
tion in chemical applications, which include PLA poly-
mer and new »green« solvents, such as ethyl lactate, is
expected to expand 19 % per year (96).
There are several major manufacturers of fermenta-
tive lactic acid, including Purac (Netherlands), Galactic
(Belgium), Cargill (USA), and several Chinese compa-
nies (91,92). In late 1997, Cargill joined forces with Dow
Chemical and established a Cargill-Dow PLA polymer
venture, NatureWorks LLC, which exists today as a stand-
-alone company. In early 2002, NatureWorks LLC com-
pleted the construction of a PLA plant that has the ca-
pacity of producing 140 000 (metric) tonnes of PLA per
year. Moreover, NatureWorks LLC has recently con-
structed a major lactic acid facility in Blair, Nebraska,
USA, which has the capacity of producing 180 000 (met-
ric) tonnes of lactic acid per year, and it began operating
in late 2002 (96,97). NatureWorks LLC has stated pub-
licly its belief that the PLA market will reach 500 000
(metric) tonnes per year worldwide by 2010, and the con-
struction of two additional PLA plants are being consid-
ered presently (12,97,98).
On an industrial scale, the manufacturing cost of lac-
tic acid monomer will be targeted to less than 0.8 US$/kg,
because the selling price of PLA should decrease rough-
ly by half from its present price of 2.2 US$/kg. Accord-
ing to the cost analysis by Datta et al. (4), although their
analysis was sensitive to various factors such as plant
size, raw material cost, and capital investment, the base
manufacturing cost of lactic acid was estimated to be 0.55
US$/kg. However, there are still several issues that need
to be addressed in order to produce lactic acid biotechno-
logically within the targeted cost, such as the develop-
ment of high-performance lactic acid-producing micro-
organisms and the lowering of the costs of raw materials
and fermentation processes. The biotechnological proces-
ses for the production of lactic acid from cheap raw ma-
terials should be improved further to make them com-
petitive with the chemically-derived one.
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