Maximizing dopa-oxidase activity in Aspergillus oryzae mycelia: insights into production optimization and potential...

The present research work is concerned with the production and optimization of the dopa-oxidase enzyme by using pre-grown mycelia of Aspergillus oryzae. Different strains of A. oryzae were collected and isolated from various soil samples. Out of 32 isolated strains, isolates 19 and 27 were selected as they showed higher dopa-oxidase activity. Biomass harvesting was accomplished in a medium containing chloramphenicol as an antibiotic. The mycelia were filtered, washed with cold water, and stored at 4 ºC. A dopa-oxidase assay was performed, and absorbance was measured at a wavelength of 505 nm. Different physical parameters such as medium pH (6), temperature (30 ºC), and inoculum size (1.5% v/v) were optimized after the results of the assay. Other parameters like nitrogen requirements, biomass level (2 mg/ml), L-tyrosine (3.75 mg/ml), and L-ascorbic acid (8.75 mg/ml) concentrations were evaluated by reaction procedure. Certain micro and macronutrients and stabilizers, including Rochelle salt (20 µM), glycerol (25 µM), orthophosphoric acid (15 µM), and ethanol (20 µM), can also increase dopa-oxidase activity. In the last stage, the time of incubation (48 h) was optimized for maximum dopa-oxidase activity as well as L-dopaquinone production. Hence, from the results of the present study, it was observed that the activity of dopa-oxidase could be increased in the reaction mixture by the addition of various substances. They enhanced the dopa-oxidase activity up to 34.18 and 29.02 U/ml for isolates 19 and 27, respectively. In the future, dopa-oxidase can be used to produce stable L-dopaquinone from L-phenylalanine, which will provide clinical applications.