Innovative use of Mucuna monosperma (Wight) callus cultures for continuous production of melanin by using statistically optimized biotransformation medium

• Innovative use of callus cultures for melanin production by biotransformation.
• Novel use of statistically optimized medium for melanin production.
• First report of continuous melanin production using laboratory scale column.
• Maximum rate of melanin production using M. monosperma callus cultures.
• Development of economic biotransformation procedure of melanin production.

Melanins are predominantly indolic polymers which are having extensive applications in cosmetics, agriculture and medicine. In the present study, optimization of nutritional parameters influencing melanin production by Mucuna monosperma callus cultures was attempted using the response surface methodology (RSM). Standardization of four factors was carried out using the Box–Behnken design. The optimized levels of factors predicted by the model include tyrosine 0.978 g L−1, pH 5.85, SDS 34.55 mg L−1and copper sulphate 21.14 mg L−1 tyrosine, which resulted in highest melanin yield of 0.887 g L−1. The optimization of medium using RSM resulted in a 3.06-fold increase in the yield of melanin. The ANOVA analysis showed a significant R2-value (0.9995), model F-value (1917.72) and probability (0.0001), with insignificant lack of fit. Optimized medium was used in the laboratory scale column reactor for the continuous production of melanin. Uninterrupted flow column exhibited maximum melanin production rate of 250 mg L−1 h−1 which is the highest value ever reported using plant as a biotransformation source. Melanin production was confirmed by spectrophotometric and chemical analysis. Thus, this study demonstrates the production of melanin by M. monosperma callus, using a laboratory scale column reactor.