L-Amino acid oxidase from filamentous fungi: screening and optimization

Twenty-seven fungal isolates recovered on medium containing -lysine were found to have the potentiality for producing extracellular -amino acid oxidase (L-AAO). displayed the highest yield of enzyme (2.6 U/mg protein) and antioxidants (2.3 mg/ml) followed by and . Upon optimization of the fermentation medium, the maximum enzyme yield (4.6 U/mg protein) was obtained on a medium containing -lysine (80 mM), glucose (0.6\%), KH2PO4 (0.1\%), KCl (0.05\%) and MgSO(4)a <...7H(2)O (0.05\%), pH 7.0, under submerged conditions. Supplementing the medium with K+, Ni2+ and Cu2+ ions increased enzyme biosynthesis by about twofold compared to the control. The activity of extracellular L-AAO from the submerged cultures of was twofold higher than that of the intracellular L-AAO. Eleven agro-industrial byproducts were tested as substrates under solid state fermentation conditions; of these, rice bran (3.3 U/mg) was the optimum solid substrate for the induction of L-AAO and antioxidants, followed by wheat bran (2.8 U/mg) and cotton seed cake (2.5 U/mg), possibly due to their higher crude protein content than ash and fiber. Glucose (1\%) and -phenylalanine were the best co-metabolic and co-inductive carbon and nitrogen source, respectively, for maximum L-AAO production by under solid state fermentation, at an initial pH of 7.0. The productivity of L-AAO by under solid state fermentation was higher than that of the submerged cultures by about 1.4-fold under optimum conditions, justifying the former fermentation processes for overproduction of this enzyme in terms of both economics and practicality.