Evolution of Citric Acid Production
Citric acid, an highly used organic compound, has undergone significant advancements in its production methods over several decades. The transition from chemical synthesis to microbial fermentation has been pivotal, driven by the pursuit of more sustainable and cost-effective production techniques. Currently, microbial fermentation dominates citric acid production, utilizing the capabilities of various microorganisms to achieve high yields efficiently.
Microorganisms in Citric Acid Production
A wide range of microorganisms, including bacteria, fungi, and yeasts, are utilized in the industrial production of citric acid. Among these, Aspergillus niger is the most commonly employed organism in the industry. This fungus is preferred due to its ease of cultivation, ability to ferment various inexpensive raw materials, and high yield efficiency.
Fermentation Methods for Citric Acid Production
Fermentation is the most economical and widely adopted method for citric acid production in the industry. There are three primary types of fermentation processes:
1. Surface Fermentation
2. Submerged Fermentation
3. Solid-State Fermentation
Notably, 99% of the global citric acid production through microbial processes is achieved via surface or submerged fermentation methods.
Surface Fermentation
In surface fermentation, *Aspergillus niger* is typically grown on solid substrates such as rice bran or other sugar-containing materials in shallow pans made of aluminum or stainless steel. Special strains of *Aspergillus niger* are selected for their ability to produce citric acid efficiently, even when there are high levels of trace metals present in the substrate.
Submerged Fermentation
Submerged fermentation involves cultivating microorganisms in a liquid medium inside fermentation tanks. The culture is aerated with air bubbles, promoting microbial growth over a period of 5 to 14 days at temperatures ranging from 27 to 33°C. This method is favored for its ability to produce large quantities of citric acid, which is then purified from the fermentation broth.
Citric Acid Upstream Tree
