Steroids are derivatives of the triterpenoid squalene, containing three fused cyclohexane rings and a cyclopentane ring, and flavonoids are derivatives of L-phenylalanine, containing two aromatic rings joined by a three-carbon bridge that may form part of a heterocyclic ring. A great variety of steroids and flavonoids are produced by plants, and many additional steroids are produced by animals or fungi. Because these compounds have many nutritional and pharmaceutical values, and many of them cannot be produced by chemical synthesis, biotechnological processes are being developed that use cultures of Aspergillus niger and other fungi to transform steroids and flavonoids to a variety of metabolites. These biochemical reactions, including hydroxylation, dehydrogenation, O-methylation, demethylation, cleavage of rings, epoxide hydrolysis, double bond reduction, and others, may be used for the production of higher-value compounds.
Applied Biochemistry and Biotechnology V.176, N 3, P.903-923