Citric acid is the most produced organic acid measured
in tonnage. Its production has now reached 1.4
million tonnes per year and continues to increase more
each year. The main reason for constant increase is the
large number of applications that can be found for citric
acid, mainly in the food and pharmaceutical industries.
Traditional processes, such as the submerged fermentation
using the fungus Aspergillus niger, dominate the global
production. However, different techniques of production
are continuously being studied showing new perspectives
for the production of citric acid. In this context,
solid-state fermentation appears where agro-industrial
residues can be used as substrate-supports to the filamentous
fungi Aspergillus niger. Significant optimization
of all citric acid processes can be observed with genetic
amelioration of producer strains, which nowadays is the
powerful tool of the citric acid market.