L-Ascorbate, a strong inducer of L-dopa (3,4-dihydroxy-L-phenylalanine) production from pre-grown mycelia of Aspergillus oryzae NRRL-1560.

The inductive effect of L-ascorbate on the microbiological production of L-dopa (3,4-dihydroxy-L-phenylalanine) from Aspergillus oryzae NRRL-1560 was investigated. All biochemical reactions were performed aerobically using mould mycelia as a source of enzyme tyrosinase and acetate buffer (pH 3.0) as an extractant. L-Tyrosine as a substrate was added at a level of 2.5 mg/ml. Maximal L-dopa production (1.876 mg/ml) was achieved when L-ascorbate (5.0 mg/ml) was added 6 min after the initiation of the biochemical reaction at 50 degrees C, consuming 2.144 mg/ml L-tyrosine. The performance of fuzzy-logic control of the reaction was found to be highly promising for improvement of the substrate conversion rate (~80%). After optimizing the reaction conditions, particularly the addition of L-ascorbate, an increase in L-dopa yield of 22.96% was achieved compared with the control (without ascorbate addition) when the process variables, namely buffer pH, L-tyrosine concentration and reaction temperature, were further identified using a two-factorial Plackett-Burman design.