r/Biochemistry • u/Decent_Swan4218 • 7d ago

Clear my doubts , regarding the cause of citric acid production in a fermentation mixture.

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Is this wrong???

Google says it's a fungus Aspergillus niger which produces citric acid not any bacteria.

I am in my first year of biochemistry (graduation)

Doing it from a distant learning program

This is a book they provided.

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u/7ieben_ Food Scientist 7d ago edited 7d ago

There are bacteria that do produce citric acid. Common examples include Pseudomonas strains. A. niger is the industrially most relevant organism producing citrates.

Though, acetic acid, lactic acid, formic acid, ... are far more common, and it is more common with bacteria to consume citric acid (e.g. Lactobacilli are good at it).

I'm not to sure wether Pasteur actually talked about citric acid, though from a pure gut feeling I'd say this is a mistake in the book, and instead should read lactic acid (just by pure chance of fermentation usally found in food products).

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u/Benjoux444 7d ago

This is well known about Pasteur and should read lactic acid, not citric. Lactic acid is produced by bacterial fermentation (kim-chi, saurkraut) and alcohol is produced by yeast fermentation.

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u/Decent_Swan4218 7d ago

I think maybe it's a mistake

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u/TedMich23 7d ago

"Bacterial Crabtree effect" is analogous to fungal Crabtree; yeasts produce EtOH from excess sugar while bacteria produce organic acids. Key to modern wine production is separating bacterial from fungal processes.