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

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Abstract
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.