Effect of manganese and other heavy metals on submerged citric acid fermentation of molasses

The addition of as little as 2 ppb of manganese to ferrocyanide-treated beet molasses during citric acid fermentation by Aspergillus niger NRC A-1-233 caused a 10% reduction in acid yield and undesirable change in the morphology of the organism from the normal pelletlike form to the filamentous from. Still smaller additions (0.4-2ppb) caused undesirable pellet clumping, while greater additions (2-100 ppb) gave further decreases in yield. The yield obtained at 100 ppb was less than 25% of that obtained at 1 ppb or less. None of the other metals tested (Al³⁺, Ca²⁺, Co²⁺, Cu²⁺, Fe²⁺, Mg²⁺, Ni²⁺, Zn²⁺) visibly changed pellet morphology, and only Al³⁺, Fe²⁺, and Zn²⁺ at relatively higher concentrations (5–25ppm) reduced acid yield. The adverse effect of manganese on growth and acid production was not affected by addition of the other metals.