One-pot green synthesis of eumelanin: process optimization and its characterization

Abstract

Advances in biocatalysis could help lower the environmental footprint of chemical processes. In this context, the present study reports for the first time the use of the Taguchi design of experiment methodology for optimizing the one-pot synthesis of eumelanin, using tyrosinase enzyme from Amorphophallus campanulatus and L-Dopa as the substrate. Using the Taguchi approach, an L₂₇ orthogonal array was applied and five critical parameters/factors—pH, temperature, oxygen level, reaction time and enzyme units—were selected for the optimization. In order to maximize the response, the signal to noise (S/N) ratio related to the larger the better was used. The main effect and interaction plots of various factors were analyzed. Response tables and ANOVA revealed that pH is the most significant factor for melanin synthesis (P < 0.05). The yield of melanin and the rate of production under the best conditions were 1176 ± 3.2 mg L⁻¹ and 24.5 mg L⁻¹ h⁻¹, respectively. Further, the biosynthesized melanin was characterized using various analytical techniques. The empirical formula of the synthesized melanin was found to be C₈H₈O₄N. Based on the elemental analysis and A₆₅₀/A₅₀₀ ratio, the biosynthesized melanin was determined to be indole-type eumelanin. Thus, the present study describes the means to increase the yield of melanin.