Lec 7 - Citric Acid Production

Question 1

What are the uses of Citric Acid (CA) in industry?

Answer 1

• food industry - beverages
• pharmaceuticals - anti coagulants
• cleaning agents (harmless to environment because broken down)

Question 2

What is the general format process for CA production and what is the final yield value normally?

Answer 2

CSTR

> 70% yield of theoretical value

Question 3

Give the organism that is exploited to produce CA

Answer 3

fungus - Aspergillus niger

Question 4

What conditions is A. niger grown in in order to get an overproduction of CA?

Answer 4

rich C medium
low pH
high concn of dissolved O2
suboptimal concs of metals/N/phosphates

Question 5

Originally, what were the names of the 2 enzymes that if inhibition occurred to was thought to lead to a build up of CA?

Answer 5

aconitase (citrate -> isocitrate)

isocitrate lyase

Question 6

instead of inhibiting enzymes to obtain more CA what is an alternative way of doing this?

Answer 6

enhancing the synthesis of CA

Question 7

How does an accumulation of CA occur ?

Answer 7

• initial C source involves waste products from sugar cane and sugar beet refining (molasses)
• high initial sugar conc needed for increased yields (around 14-22%)
• high sugar concn leads to repression of a ketoglutarate dehydrogenase (another enzyme in Krebs cycle) leading to a build up of intermediates and accumulation of citric acid