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Fermentation process for the production of citric acid
| Details |
Inventors: Nubel, Robert; Fitts, Robert; Findlay, Gordon;
Assignee: Pfizer Inc. (New York, NY)
Primary Examiner: Shapiro; Lionel M.
Assistant Examiner:
Attorney, Agent or Firm: Connolly and Hutz
A process for producing citric acid directly in the free acid form by aerobically fermenting an aqueous hydrocarbon-containing nutrient medium at a low pH with a new strain of the yeast, Candida lipolytica. |
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DETAILED DESCRIPTION OF THE INVENTION It has now been found that a certain strain of the yeast Candida lipolytica has the peculiar ability to accumulate citric acid in the free acid form, during the aerobic fermentation of aqueous media containing a hydrocarbon as the principal or sole source of assimilable carbon, provided however that the pH of the fermentation is kept low, i.
e.
, the citric acid is not neutralized as it is produced.
At the present time only the one strain of lipolytica is known which permits direct crystallization of citric acid from the concentrated broth.
Most publicly available strains have been tested and found not to possess this unique property.
The operable strain has been deposited in a recognized public collection, the American Type Culture Collection, and given the number ATCC 20,228.
To take the fullest advantage of this property of the culture, fermentation is conducted at low pH, i.
e.
, without neutralizing the citric acid produced.
It is surprising but true that the strain No.
20,228 remains viable and a strong citric acid-producer even at pH's of about 2-3 or even lower.
Initially, it is necessary to maintain a pH of about 4-7 (usually about 5-6) to permit cell growth to occur.
However, after the cell mass is developed, the pH is allowed to fall naturally, as more citric acid is produced without adding more buffer or other base to react with the product.
The fermentation is usually complete in 5-7 days.
Before the first 2 days have passed, the pH is already below 4, and it continues to fall to a final range of about 2-3 as more acid is produced.
As previously noted, this means that most of the product is already in the form of the free acid, not a citrate, and is ready to be recovered.
The initial pH maintenance could be effected by adding caustic or other base.
However, it is most convenient to simply add a limited amount of a carbonate at the outset, such that its buffering capacity will have been consumed by citric acid produced at about the time that the cell mass is developed adequately to use as inoculum for the fermentation
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Molecular Biology 
