Growth and kojic acid production byAspergillus flavus growing on peanut oil

Summary

A procedure was described for the quantitative study of oil and fatty acid utilization by fungi.Aspergillus flavus was demonstrated to grow well when peanut oil, or various components of peanut oil, were supplied as single sources of carbon. The effect of various environmental factors on growth and kojic acid production byA. flavus was studied. It was concluded that the most reliable index of growth was the production of lipid-free mycelium. Measurements of total mycelial dry weight proved to be an unreliable index of growth because they included varying quantities of oil absorbed but not metabolized. Optimum conditions for oil utilization and growth were: initial pH, 5.0 to 9.0; temperature, 20 to 40°C; substrate-oil concentration, 3.4% or higher; and surface area to volume ratio, 0.56 (50 ml. of media in 125-ml. flasks). Optimum conditions for kojic acid production were: pH, 7.0 to 8.0; temperature, 30 to 35°C; substrate-oil concentration, 3.5%; and surface area to volume ratio, 0.56. Kojic acid was not synthesized when inorganic salts were supplied as single nitrogen sources.

Nitrogen sources suitable for kojic acid synthesis were : yeast extract, casein, peptone, alanine, tryptophan, glutamic acid, and to a lesser degree proline. Other commonly used amino acids and amides were not suitable for acid synthesis, although certain ones supported good growth. The addition of KH₂PO₄ to the medium inhibited acid production and to a lesser degree inhibited growth.