Statistical design for biogenesis of melanin nanoparticles from producer strain Pseudomonas stutzeri BTCZ 109 through Taguchi DOE

Melanins are a group of biological macromolecules synthesized by a wide spectrum of living organisms mainly through oxidative polymerization of indolic and phenolic compounds. Because of its various properties including antioxidation, antibiofilm, metal chelation, UV protection and anticancer activity it has widespread application in agriculture, cosmetic and therapeutic industries which makes it commercially valuable and its large-scale production attain enormous consideration. The phylogenetic analysis reveals that the organism belongs to Pseudomonas stutzeri strain (BTCZ 109). Taguchi method of design of experiment (DOE) using Qualitek-4 software for the optimization of parameters to enhance melanin production was carried out in this study. L⁸ (2⁷) type of Orthogonal Arrays (OA) was constructed using 7 variables including incubation time (days), inoculum concentration (%), pH, MgSO₄.5H₂O (mM), l-tyrosine (g/l), temperature (⁰C) and agitation (rpm). Maximum melanin production through different combinations of experimental variables, factors contributing to production and interaction among the selected factors at their given levels, were elucidated. 8 trials of experiments were performed under the L-8 Orthogonal Array (OA) designed by the Taguchi approach. The experimental data were analyzed using the Signal-to-noise (S/N) ratio with the ‘bigger is better’ characteristics to identify the influential parameters and to establish the optimum conditions for maximizing melanin production. Validation of the predicted data with the confirmatory experiments revealed a nominal value of 1328.855 μg/mL, with an average performance of 1158.27 μg/mL, at the optimized condition of incubation time 4 days, pH 8, temperature 35 °C, agitation 140 rpm, and MgSO₄.5H₂O (mM) 0.25 mM absorbance units (AU) of OD₄₀₀. The melanin thus obtained was found to be nano-sized and which reveals its pharmaceutical, biomedical and environmental application.