Comparative study of a new alkaline L-methioninase production by Aspergillus ustus AUMC 10151 in submerged and solid-state fermentation

Abstract

Twenty four fungal species were screened for their ability to produce alkaline L-methioninase on methionine-glucose liquid medium. Aspergillus ustus AUMC 10151 displayed the highest yield of enzyme (10.8 U/mg protein), followed by A. ochraceus and Fusarium proliferatum. Upon optimization of the submerged fermentation (SmF)conditions, the maximum enzyme yield (18.23 U/mg protein) was obtained on a medium containing L-methionine (0.5%), sucrose (0.95%), KH2PO4 (0.1%) and 175 rpm. Seven agro-industrial by-products were screened as substrates for L-methioninase production under solid-state fermentation (SSF). Wheat bran resulted 38.1 U/mg protein, followed by rice bran (27.6 U/mg protein) and soya bean meal (26.6 U/mg protein). Maximum alkaline L-methioninase (99.56U/mg protein) was achieved at initial moisture content of 71.5%, inoculum size of 2.0 mL of spore suspension, initial pH 8.5, incubation period eight days at 30°C and supplementation of the salt basal medium with pyridoxine(100 μg/mL) and beet molasses (20% v/v). The productivity of L-methioninase by A. ustus under SSF was higher than that of SmF about 5.45 fold under optimum conditions.