This document summarizes the microbial production of organic acids like citric acid and lactic acid. Citric acid is produced industrially through surface or submerged fermentation of Aspergillus niger and can be used as a food acidulant or in processed foods. Lactic acid is produced through fermentation of Lactobacillus bacteria or Rhizopus fungus and used in baking, medicine, and plastics manufacturing. The fermentation processes, extraction methods, and purification steps for both citric acid and lactic acid production are described at a high level.

1. Microbial production of
Organic acids
Presented by
Swetha S Menon
2nd Botany

2. INTRODUCTION
• A large number of organic acids with actual or
potential uses are produced by
microorganisms. Citric, itaconic, lactic, malic,
tartaric, gluconic, mevalonic, salicylic,
gibberellic, diaminopimelic, and propionic
acids are some of the acids whose microbial
production have been patented.

3. i. Citric Acid
• Citric acid is a tribasic acid
citric acid structure

4. • It crystallizes with the large rhombic crystals
containing one molecule of water of
crystallization, which is lost when it is heated
to 130°C. At temperatures as high as 175°C it
is converted to itaconic acid, aconitic acid, and
other compounds.

5. Uses of Citric Acid
• (i) Citric acid is the major food acidulant used
in the manufacture of jellies, jams, sweets,
and soft drinks.
• (ii) It is used for artificial flavoring in various
foods including soft drinks.
• (iii) Sodium citrate is employed in processed
cheese manufacture

6. Biochemical Basis of the Production
of Citric Acid
• Citric acid is an intermediate in the citric acid
cycle (TCA). The acid can therefore be caused
to accumulate by one of the following
methods;
• By mutation
• By inhibiting the free-flow of the cycle through
altering the environmental conditions

7. Fermentation for Citric Acid
Production
• Fermentation is the most economical and
widely used ay for synthesis citric acid
production.
• The industrial citric acid production can be
carried in three different ways: surface
fermentation submerged fermentation

8. (a) Surface fermentation
• Surface fermentation using Aspergillus niger
may be done on rice bran as is the case in
Japan, or in liquid solution in flat aluminium or
stainless steel pans.
• Special strains of Aspergillus niger which can
produce citric acid despite the high content of
trace metals in rice bran are used.

9. SUBMERGED FERMENTATION
• In this case , the strains are inoculated of
about 15cm depth in fermentation tank.
• The culture is enhanced by giving aeration
using air bubbles.
• And its allowed to grow for about 5 to 14 days
at 27 to 33 degree Celsius.
• The citric acid produced in the fermentation
tank and it is purified.

10. Separation
• The biomass is separated by filtration.
• The liquid is transferred to recovery process
• Separation of citric acid from the liquid
precipitation.
• Calcium hydroxide is added to obtain calcium
citrate.

11. • Tetra hydrate Wash the precipitate Dissolve it
with dilute sulfuric acid, yield citric acid and
calcium sulfate precipitate Bleach and
crystallization Anhydrous or mono hydrate
citric acid Separation process

12. PURIFICATION
• Purification is a simple form of getting a pure
citric acid followed by two simple techniques
Precipitation &Filtration
React citric acid
with calcium
carbonate
Filter precipitate
Filter
precipitate
React precipitate
with sulfuric acid
Purified
citric Acid

13. Lactic Acid
• Lactic acid is produced by many organisms:
animals including man produce the acid in
muscle during work.

14. Uses of lactic acid
• It is used in the baking industry. Originally
fermentation lactic acid was produced to
replace tartarates in baking powder with
calcium lactate. Later it was used to produce
calcium stearyl-2lactylate, a bread additive.
• In medicine it is sometimes used to introduce
calcium in to the body in the form of calcium
lactate, in diseases of calcium deficiency.

15. • Esters of lactic acid are also used in the food
industry as emulsifiers.
• Lactic acid is used in the manufacture of rye
bread.
• It is used in the manufacture of plastics.

16. Fermentation for lactic acid
• Although many organisms can produce lactic
acid, the amounts produced are small; the
organisms which produce adequate amounts
and are therefore used in industry are the
homofermentative lactic acid bacteria,
Lactobacillus spp., especially L. delbrueckii.
• In recent times, Rhizopus oryzae has been
used.

17. • Both organisms produce the L-form of the acid, but ,
• Rhizopus fermentation has the advantage of being
much shorter in duration; furthermore, the isolation of
the acid is much easier when the fungus is used.
• Although lactic fermentation is anaerobic, the
organisms involved are facultative and while air is
excluded as much as possible, complete anaerobiosis is
not necessary. The temperature of the fermentation is
high in comparison with other fermentations and is
around 45°C. Contamination is therefore not a
problem, except by thermophilic clostridia.

18. Extraction
• The fermentation broth is filtered by using
porcelain filters to separate the bacterium.
• The filtrate is acidified with sulphuric acid to
regenerate lactic acid, to precipitate calcium
as calcium sulphate and is washed.
• .The washed filtrate is treated with activated
carbon to remove organic impurities.

19. • Repeated refining and evaporation steps are
undertaken to get higher percentage of lactic
acid to the extent of 50-60%.
• It is then treated with ferrocyanide to
remove heavy metals, if any, like copper.
• It is finally purified by passing through ion
exchange resins.

20. MANY OF ORGANIC ACIDS ARE FOUND
IN LIVING THINGS

21. REFERANCE
• https://www.researchgate.net/publication/27
1534193_Microbial_production_of_lactic_aci
d
• https://gcwgandhinagar.com/econtent/docum
ent/1587535005Unit%20III%20Microbial%20p
roduction%20of%20organic%20acids.pdf