Bioconversion of L-phenylalanine to L-dopaquinone by Aspergillus oryzae: a scalable model for neurological precursor synthesis.

This work explores an improved fungal-mediated bioconversion method for generating stable L-dopaquinone from L-phenylalanine using two Aspergillus oryzae strains (ISL 19 and ISL 27) and mycelial biomass. Mycelial biomass produced through submerged fermentation was exposed to controlled reaction setups to evaluate dopa-oxidase activity and resulting product formation. Quantification of L-dopaquinone was performed using dopachrome and dopa-oxidase assays, measured at 475 nm and 505 nm. Through systematic optimization of cultural and nutritional variables, the highest yield was obtained after 48 h of incubation at pH 6.0 and 30 °C. Among the tested nitrogen sources, urea (0.04% w/v), ammonium sulfate (0.12% w/v), and yeast extract (0.75% w/v) markedly improved the biotransformation process. Carbon-source optimization identified L-tyrosine (3.75 mg/mL) and L-ascorbic acid (8.75 mg/mL) as the most effective concentrations. Under the optimized conditions, strain ISL 27 produced a maximum L-dopaquinone level of 29.75 µg/mL. Stabilizing agents-including ethanol, ortho-phosphoric acid, potassium-sodium tartrate, and glycerol-further boosted enzyme efficiency and product stability. Overall, the findings highlight A. oryzae as a promising biocatalyst for L-dopaquinone synthesis, supporting potential applications in pharmaceutical, cosmetic, and neurochemical fields. The study offers an environmentally friendly and scalable strategy for L-dopaquinone production and provides a framework for future research on fungal enzyme systems involved in neuroactive compound biosynthesis.