Zeolite Membrane Bio-Reactor for L-DOPA Production

L-DOPA is an effective drug in the treatment of Parkinson's disease, a neurological disorder which has a particular impact in elderly people. Nowadays, this drug is chemically produced (Monsanto process). Because of the high production cost and its commercial value, many researchers have investigated an alternative route for its production. For example, some investigations focussed on the microbiological production of L-DOPA from Erwinia herbicola [1.2] and Escherichia coli [3,4]. However, the need for the purification steps required to remove proteins and metabolic by-products, produced by these micro-organisms, and the low concentration of the drug in the product stream increase the cost of the microbial synthesis, making it economically unfeasible. A more promising way is the enzymatic conversion of the L-tyrosine using the immobilised tyrosinase as enzyme [5]. Enzyme immobilization leads to the increase of enzyme stability and its re-use in successive reaction cycles, lowering the total production cost. Different papers dealt with the immobilization on polymeric membranes [6, 7]. However, the use of molecular sieves offers interesting properties, such as high surface area favouring high enzyme loading [8], and the establishment of hydrophobic or hydrophilic interactions allowing for a better compatibility between enzyme and support, as well as good mechanical and chemical resistance. Furthermore, the inorganic membranes can be regenerated easily and reused in case of deactivation of the enzyme. In this work for the first time zeolite membranes are used for the L-DOPA production. The use of tyrosinase immobilised on these materials has several advantages over other support types. In particular, zeolites are excellent free radical trapping agents. Since free radicals, derived from oxygen and responsible for the tyrosinase inactivation, are trapped in these materials and consequently the stability of the enzyme is enhanced. The effect of the immobilization conditions on tyrosinase activity were investigated and the conversion degree was also measured and compared with the traditional batch reactor.