A kinetic model describing melanin formation by means of mushroom tyrosinase

Melanins are an heterogeneous group of polymers formed by enzymatic reactions in vegetable tissues containing phenolic or polyphenolic molecules. Recent studies have discovered some beneficial properties of melanins on health, such as anti-oxidative, anti-inflammatory, immune and anti-tumor properties, so not only its elimination should be reconsidered, but also its addition could be proposed to functional food of new creation. Then, a further knowledge about the kinetic mechanism of melanogenesis is required prior to its possible industrial utilization. In this work, an autocatalytic kinetic model to explain melanin formation from l-tyrosine using mushroom tyrosinase and measuring the absorbance of the solution has been developed and fitted to experimental data. This expression allows to describe melanin formation as a function of time of reaction, including some important parameters such as the extinction coefficient. Absorbance will start growing after a lag period in which colorless intermediates are produced. The extinction coefficient of the resulting products is not a constant value, because it depends on the conditions of each experiment. Tyrosinase seemed to have a lower catalytic effect on l-tyrosine than on L-DOPA.