Citric acid also called 2-hydroxy-propane-1,2,3-tricarboxylic acid, is a component of the tricarboxylic acid cycle in all organisms. Industrial production of citric acid use fungal, yeast and citrus fruit as the major source. Aspergillus niger is majorly used for citric acid production by fermentation Manganese inhibits fermentative production of citric acid Oral supplementation of citric acid promotes tricarboxylic acid cycle and oxidative phosphorylation in mitochondria, attenuating physical fatigue.