Maarg Manthan · Topic 11.24

Organic Acids and Polysaccharides Production

Science & Technology › Biotechnology – Applications · Topic 11.24

Organic acids and microbial polysaccharides are bulk chemicals made by fermentation. The main organic acids are citric acid, produced by the mould Aspergillus niger and used in food, drinks and medicines, lactic acid, produced by Lactobacillus and used in food and in the plastic polylactic acid, acetic acid from Acetobacter, gluconic acid from Aspergillus niger, and itaconic acid from Aspergillus terreus. Microbial polysaccharides, which are long chains of sugars, include xanthan gum from Xanthomonas campestris, dextran from Leuconostoc mesenteroides, pullulan from Aureobasidium pullulans, gellan gum and alginate. They are used as thickeners, stabilisers and gels in foods, medicines, oil drilling and cosmetics.

5 min read · UPSC Prelims · Science & Technology · Biotechnology – Applications

At a Glance

Citric acid Aspergillus niger
Lactic acid Lactobacillus
Xanthan gum Xanthomonas campestris
Dextran Leuconostoc mesenteroides
Bioplastic Polylactic acid
Exam link UPSC Prelims, Science & Technology: Biotechnology – Applications

Where Does It Fit?

This topic follows the amino acid and vitamin topic. It lists two more groups of bulk products made in fermenters, organic acids and sugar polymers, that appear in almost every industry. Previous topic: Amino Acids, Vitamins and Sweeteners from Biotechnology. Next topic: Public Acceptance and Safety of New Biotechnology Foods.

Which Organic Acids Are Made and Used?

Acid	Microbe and uses
Citric acid	Aspergillus niger grown on molasses or starch. The most produced organic acid. Used in drinks, sweets, jams, medicines and cleaners
Lactic acid	Lactobacillus species. Used in food, leather, and for polylactic acid, a biodegradable plastic
Acetic acid	Acetobacter oxidises alcohol. Used as vinegar and in chemical industry
Gluconic acid	Aspergillus niger. Used in cleaning, in medicines as calcium gluconate and in concrete additives
Itaconic acid	Aspergillus terreus. Used for making resins and polymers
Propionic acid	Propionibacterium. Used as a preservative against mould in bread
Succinic acid	Made by engineered microbes as a building block for plastics and solvents

Which Polysaccharides Are Made and Used?

Xanthan gum: from Xanthomonas campestris grown on glucose. A thickener for sauces, salad dressings and gluten free baking, and used in oil drilling muds
Dextran: from Leuconostoc mesenteroides acting on sucrose. Used in medicine as a blood plasma volume expander and in chromatography media
Pullulan: from the fungus Aureobasidium pullulans. Forms edible films and capsules
Gellan gum: from Sphingomonas elodea. A gelling agent in desserts, drinks and tissue culture media
Alginate: from brown seaweed and from bacteria like Azotobacter. Used for gels and to immobilise enzymes and cells
Curdlan: from Alcaligenes faecalis. Forms firm gels on heating
Hyaluronic acid: made by Streptococcus or engineered bacteria, used in medicine and cosmetics
Bacterial cellulose: made by Komagataeibacter, used in food such as nata de coco and in wound dressings

What Else Should You Remember?

Citric acid production: fermentation can be surface, submerged or solid state, and submerged culture in large stirred tanks gives most of the world supply
Why fermentation: most citric acid now comes from fermentation, not from extraction from lemons
Polylactic acid: a bioplastic made by joining lactic acid units. It is compostable under industrial conditions and used for packaging and 3D printing
Polyhydroxyalkanoates: plastics stored inside bacteria such as Ralstonia eutropha as energy reserves, which are fully biodegradable
Single use plastic ban: India banned identified single use plastic items from July 2022, which raises interest in alternatives such as bioplastics
Starch and sugar substrates: molasses, corn starch and agricultural waste are common feedstocks, as in National Policy on Biofuels,…">Biofuels: Bioethanol, Biodiesel and Biogas from Biomass
Downstream steps: citric acid is recovered by adding calcium, precipitating calcium citrate, and treating it with sulphuric acid
Food additive numbers: many acids and gums have E numbers and are approved food additives, which FSSAI regulates
Dextran in medicine: used to treat shock, but can cause allergic reactions
Biosurfactants: microbes also make surface active agents, such as rhamnolipids, used for oil spills
Indian industry: India produces citric acid and lactic acid, and imports many gums, so local capacity is limited
Link: microbial growth in tanks follows the concepts in Bioprocess and Fermentation Technology
Primary metabolites: citric and lactic acid are made during active growth, so their fermentation is tuned for rapid sugar use
Trace metals: citric acid yield by Aspergillus niger falls if iron and manganese are present at wrong levels, so media are treated carefully
Edible films: pullulan and alginate films dissolve in water or the mouth, and are being used for breath strips and capsules
Sustainability: using agricultural waste as feedstock lowers cost and avoids competition with food crops
Regulatory status: food grade gums and acids must meet purity standards before approval for use in food in India

Why Does It Matter for the Exam?

Match microbe with product: Aspergillus niger, Leuconostoc, Xanthomonas
Uses: food, medicine, plastics
Bioplastics: PLA and PHA
Current affairs link: plastic bans and biodegradable packaging
Common errors: saying that citric acid is mainly extracted from lemons today

As an analytical point, fermentation based acids and gums replace petroleum based chemicals in many uses. Local production lowers import dependence, and bioplastics support the shift from single use plastics.

Why Is This Topic Important?

Acids Microbe matches
Gums Uses
Plastics PLA and PHA

What Came Next?

The next topic covers public acceptance and safety of new biotechnology foods. Next topic: Public Acceptance and Safety of New Biotechnology Foods.

Key People and Terms

Polysaccharide Long sugar chain
Thickener Raises viscosity
Bioplastic Plastic from biological source
PLA Polylactic acid
PHA Polyhydroxyalkanoate
Feedstock Raw material for fermentation

Exam Corner

Points to Remember

Citric acid: Aspergillus niger.
Xanthan gum: Xanthomonas campestris.
Dextran: Leuconostoc.
PLA from lactic acid.
PHA made inside bacteria.

Do Not Confuse With

PLA and PHA Chemically polymerised lactic acid versus bacterial granules
Citric acid and lactic acid Mould product versus bacterial product
Xanthan and gellan Thickener versus gelling agent

Memory Hook

Niger gives citric and gluconic; Leuconostoc gives dextran; Xanthomonas makes the gum.

Mains Angle

Questions ask to match microbes with products and about bioplastics. These points help.

Products Acids and gums
Uses Food to plastics
Policy Plastic alternatives

A Question You May Face

An original practice question, not a past paper question.

“Discuss the industrial importance of microbial organic acids and polysaccharides and their role in reducing plastic pollution.”

How to Answer

Products Acids, gums.
Uses Food, medicine, plastics.
Bioplastics PLA, PHA.
Way Local capacity.

GS Relevance

Prelims: microbe and product matches, uses of gums, bioplastics. GS Paper 3: biotechnology, industry, environment.

Frequently Asked Questions

Which microbe is used to produce citric acid?

The mould Aspergillus niger is used to produce citric acid on a large scale by fermenting sugar from molasses or starch, usually in submerged stirred tanks. Citric acid is the most widely produced organic acid and is used as a flavouring and preservative in food and drinks and in medicines and cleaning products.

What is xanthan gum?

Xanthan gum is a polysaccharide produced by the bacterium Xanthomonas campestris when it ferments glucose. It forms thick, stable solutions even in small amounts, so it is used as a thickener and stabiliser in sauces, dressings, gluten free baking and also in oil drilling fluids and cosmetics.

What is dextran used for?

Dextran is a polysaccharide produced by Leuconostoc mesenteroides from sucrose. In medicine, solutions of dextran are used to increase blood volume in cases of blood loss or shock. It is also used to make gel media for chromatography and has applications in the food and chemical industries.

What is polylactic acid?

Polylactic acid is a biodegradable plastic made by joining molecules of lactic acid, which is produced by bacterial fermentation of sugar or starch. It is used for packaging, disposable cutlery, fibres and 3D printing, and can be composted in industrial facilities, so it is considered an alternative to petroleum based plastics.

What are polyhydroxyalkanoates?

Polyhydroxyalkanoates are polyesters that many bacteria store inside their cells as energy reserves when food is plentiful but nutrients like nitrogen are short. They can be extracted and used as biodegradable plastics that break down in soil and water, making them a promising alternative to conventional plastics.

PYQ Practice — Statement Analysis

1 Xanthomonas campestris produces xanthan gum.

True

A bacterial polysaccharide.

2 Most citric acid today is extracted from lemons.

False

It is produced by fermentation.

3 Polylactic acid is made from lactic acid.