Lactic acid, a widely used organic acid in food, pharmaceutical, and chemical industries, is predominantly produced in its L(+)-form due to the harmful effects of the D(-)-isomer. Its production relies on microbial fermentation of renewable raw materials like glucose, starch, and other cheap organic materials, with various strains of lactic acid bacteria or fungi utilized for its synthesis. Additionally, downstream processing techniques, such as membrane filtration and continuous bioreactor systems, enhance the efficiency of lactic acid production and purification for various applications, including food preservation and biodegradable plastics.

1. NTRODUCTION:
 Lactic acid (2-hydroxypropionic, CH3CHOH-COOH) also known as milk acid which is most widely
utilized organic acid in the food, pharmaceutical, cosmetics and chemical industries.
Lactic acid exists naturally in two optical isomers:
• D(-)- lactic acid
• L(+)-lactic acid.
 Since elevated levels of the D isomer are harmful to humans. L(+)-lactic acid is the preferred
isomer for food-related and pharmaceutical industries..
 Racemic mixture (DL) results from chemical synthesis or through some lactic acid bacteria
possessing both D and L lactate dehydrogenases.
 Different stereoisomeric forms of lactic acid are produced by microbial fermentation using a specific
microbial strain.

2. Renewable raw materials:
 Molasses,
 Starch (corn starch, wheat starch, potato starch)
 Lignocellulose (corn cobs and woody materials).
 In many cases, glucose was the preferred carbon source for L-lactic acid
production by Rhizopus species, followed by starch material.
 However, as cheap and widely existing materials, dry grass, coconut husk,
sugarcane waste and wood were recognized as cost effective carbon sources for
lactic acid production.
 Substrate cost is one of the representing 30-40% of total production costs.
Substrate for Lactic acid Production:

3. Lactic Acid Bacterium Substrate
Lactobacillus delbreuckii subspecies
delbreuckii
Sucrose
Lactobacillus delbreuckii subspecies
bulgaricus
Lactose
Lactobacillus helveticus Both lactose and galactose
Lactobacillus amylophylus and L.
amylovirus
Starch
Lactobacillus lactis Glucose, sucrose and galactose
Lactobacillus pentosus Sulfite waste liquor

5. PRODUCTION OF LACTIC ACID
•The organisms responsible for the production of
lactic acid includes
•Bacteria
•Fungi
• Rhizopus sp : Utilize glucose aerobically to produce lactic
acid.
• Rhzopus species such as R. oryzae and R. arrhizus have
amylolytic enzyme activity, which enables them to convert
starch directly to L (+)-lactic acid.

6. Physiological characteristics of Lactic acid bacteria:
1) All its members are gram positive and do not form spores (with the solitary
exception of Sporolactobacillus inulinus).
2) Most of them are non motile.
3) They all are dependent on carbohydrate for their energy supply and excrete lactic
acid.
4) They do not contain haemins (cytochrome, catalase).
5) In spite of the absence of the haemins, the lactobacteriaceae especially the
streptococci can grow in the presence of oxygen. Thus they are anaerobes but
aerotolerant.
6) They require complex media containing several growth factors such as vitamins,
lactoflavin, thiamine, nicotinic acid, folic acid, biotin, pantothenic acid etc.

7. How lactic acid is produced?
Two possibilities for the synthesis of Lactic acid:
1. Chemical synthesis
2. Fermentation of solution that contains carbohydrate.
 Commercial lactic acid is produced naturally by fermentation of
carbohydrates such as glucose, sucrose or lactose.
 The problem with chemically synthesized acids is their racemic properties.
Fermented acids can produce desired isomers like L (+) and D (-) Lactic
acids(Jin et. al., 2003) which are more important in modern applications for the
acids uses such as biodegradable plastics.
 The properties that are derived from the different forms of the isomer are very
different. For instance higher optical purity of the L (+) Lactate polymer leads
to higher melting point and crystallinity.

8. 1,Chemical synthesis:
➤ The commercial process of chemical synthesis is based on lactonitrile (Narayanan et. al.,
2004).
➤ HCN is added to acetaldehyde in the presence of a base to produce lactonitrile. (liquid
phase at high pressures.)
➤ The crude lactonitrile is recovered and purified by distillation
➤ It is then hydrolyzed to lactic acid, either by conc. HCI or by H2SO4 to produce
corresponding ammonium salt and lactic acid.
➤ Lactic acid is then esterified with methanol to produce methyl lactate.
➤ Methyl lactate is removed and purified by distillation and hydrolyzed by water under acid
catalyst to produce lactic acid and methanol, which is recycled.
2.Microbial production via Fermentation:
Stereo specific lactic acid can be made by carbohydrate fermentation depending on the microbial
strain being used (Narayanan 2004).

10. There are two specific routes for fermentation depening
upon the microorganisms (Shuler, 2003)
• HOMOFERMENTATIVE GROUP
• Homofermentative Lactic acid bacteria produce pure or almost pure (90%)
lactate.
• They metabolize glucose via the fructose-bis phosphate pathway and
produce 1 molecule of Lactate from 1 molecule of glucose.
• Examples are: Lactococcus lactis, Streptococci, Enterococcus faecclis.
• HETEROFERMENTATIVE GROUP
• Heterofermentative lactic acid bacteria produce 1 molecule of lactate along
with 1 molecule of ethanol and 1 molecule of carbon dioxide (or acetic
acid).
• Examples are Leuconostoc sp., Lactobacillus brevis, Lactobacillus fermentum.

11. Bioprocess parameters in Lactic acid Production:
1. Nutrients:
 Nitrogen
 Inorganic Salts
2. pH
3. Oxygen supply
4 Temperature

12. Nutrients:
 Nutrients are the essential substances required in any fermentation process. Supplement of
sufficient carbon, nitrogen, phosphate, sulfur and other salts is vital to maintain the growth
of microorganisms and formation of products.
 In general, Rhizopus species have relatively lower nutritional demands compared with
bacteria, requiring only small amount of inorganic salts to achieve asatisfactory fermentation
performance.
 The optimum nutrient concentration depends on the nature of the substrate, the strain and the
method involved in the
Nitrogen:
 Nitrogen is needed for the synthesis of amino acids, purines, pyrimidines, some carbohydrates
and lipids, enzyme cofactors and other substances.
 Nitrogen sources can be inorganic salts, such as ammonium sulfate and ammonium nitrate,
and organic substances, such as peptone, yeast extract and corn steep liquor.
 Ammonium sulfate is the most widely used nitrogen source.

13. Inorganic salts
pH
➤ The favorable pH range is 5.0-6.0.
➤ Tay and Yang (2002) found that production. of lactic acid, ethanol and fumaric acid decreased
as pH decreased from 6.0 to 4.0.
➤ Miura et. al., (2003) results showed that the highest lactic acid yield (93 g/L) was achieved at pH
6.0-6.5.
Neutralizing agents ➤ To control the pH during the fermentation, neutralizing agents such as calcium
carbonate, sodium carbonate and sodium hydroxide need to be added into fermentation medium.

14. 3. Oxygen supply
➤ Fungal fermentation by Rhizopus species is an aerobic process and oxygen supply
plays an important role in lactic acid production.
➤ A high DO level of 70-90% was required in the fermentation medium to achieve a high
lactic acid yield and productivity.
➤ The enhanced DO level can improve the lactic acid production and limit the formation
of ethanol.

15. 4. Temperature
➤ A Huang et. al., (2003) found that R. arrhizus DAR 36017 could grow well from
22 to 38 C,
➤ Although the production of lactic acid was temperature sensitive.
➤ Lactic acid concentration was obtained at the highest level at 30 C,
➤ while biomass production decreased with increasing temperature.
➤ Liu et. al., (2005) found that 27 C was an optimal temperature for the
production of I(+)- lactic acid from cull potato by R. oryzae NRL 395 Optimum
range of temperature for lactic acid fermentation is 27-35

16. DOWNSTREAM PROCESSING
•Lactic acid can be separated and substantially purified from fermentation
broths by several membrane-based unit operations
•Microfiltration or ultrafiltration for cell separation and recycle
•Nanofiltration for separation of the lactic acid from other broth
components using low rejection (LR) membranes
•Concentrating the lactate using reverse osmosis (RO) or a
combination of high rejection (HR) and low rejection (LR)
nanofiltration membranes
•Electrodialysis (ED) for simultaneous separation and concentration
of lactate. A conventional anion-/cation-exchange membrane ED
system will purify and concentrate the lactate, but the lactate product
will still be in the salt form (if the salt form was produced in the
fermentation).
•On the other hand, a bipolar membrane ED system will result in the
acid form of lactic acid and allow the recycle of the alkali used for
neutralizing the fermentation broth. This minimizes alkali cost, as
well as eliminating the waste product (e.g., calcium sulfate) generated
in conventional downstream processes for organic acids.

17. A continuous membrane bioreactor (CMB) as a continuous stirred tank reactor (CSTR) coupled in a semi
closed loop configuration to a membrane module, as shown in the diagram below.
Synthetic semi-permeable membranes are used to separate and recycle the lactic acid bacteria,
while simultaneously removing the lactate as it is formed.
The continuous separation and recovery of the bacterial cells will reduce cycle time of the
fermenters, since there will be little or no time lost due to start-up and shut down as in present batch
fermenters.
BIOREACTOR DESIGN

18. • The recycle of the cells will allow us to obtain much higher cell densities than
currently practiced. Laboratory studies have shown a 100-fold increase in cell numbers
in the CMB during operation. The high concentration allows us to pump the feedstock
through the fermenters much faster.
• "Cell wash-out" is eliminated, thereby allowing operation at dilution rates greater than
the specific growth rate of the organism.
• The continuous removal of lactate allows us to maintain the fermenter at just below
the lactate level which inactivates the cells. Thus the cells are always viable and
producing lactate.

19. Food industries:
• Lactic acid is added to margarine, butter, yogurts etc. for its pleasant taste
(taste enhancer).
• Lactic acid is used as pickling agent for olives and pickled vegetables.It is also
used as jelling agent for jams and jellies.
• Calcium-lactate is added to milk and other sports drink as mineral supplement.
• Lactic acid and its salt can increase the shelf life of food products like
sausages, hams, poultry, fish, etc
• .A large mass fraction of (>50%) fermentation grade Lactic acid is used to
produce emulsifying agents such as sodium and calcium stearoyl lactate in
bakery goods.
• Calcium salt of this acid is a good dough conditioner and the sodium salt is both
conditioner and emulsifier for Yeast leavened bakery products.

20.  Pharmaceutical Industries:
 Poly lactic acid polymers are biocompatible, biodegradable and restorable materials
used in medical application as sutures, orthopedic implants, controlled drug release etc.
 Polymers of Lactic acid interf badljusting the composition and the molecular wt., can control
the degradation of biodegradable transparent thermoplamolec.
 Other applications in applications are formulation of ointments, lotions, anti-acne Otherons
and dialysis applications. Ca-lactate can be used for calcium, denta therapy and as anti
carries agents.
Chemical Industries:
 Lactic acid is used as acidulant in Leather tanning industries.
 In small scale operations like pH adjustments, hardening baths for cellophanes used in food
packaging, terminating agent for phenol formaldehyde resins, alkyl resin modifiers, solder
flux, lithographic and textile printing developers, adhesive formulations, in electroplating
and electro polishing baths, detergent builders etc.
 Lactic acid esters like ethyl/butyl lactates can be used as green solvents. They are high
boiling, non-toxic and degradable components.

21. Thank You