The reaction of lignin model compounds during enzymatic bleaching with a Curvularia verruculosa haloperoxidase: impact on chlorination

Recent developments in enzymatic bleaching processes have led to replacement strategies of harsh chemicals by haloperoxidases. For this purpose, it is important to control the haloperoxidase-mediated formation of adsorbable organic halides (AOX). In this study, we studied the chlorination of monomeric and dimeric lignin model substrates. Guaiacol, acetovanillone, veratryl alcohol, pinoresinol and adlerol were treated with Curvularia verruculosa haloperoxidase and compared to a sodium hypochlorite treatment. High-performance liquid chromatography-diode array detection-mass spectrometry (HPLC-DAD-MS) analysis was employed for the characterization of the reaction products. Our results show that while treatment with haloperoxidases in the presence of sodium chloride and hydrogen peroxide leads to no improvement in AOX formation compared to chemical treatment with NaOCl, addition of ammonium chloride substantially lessens chlorination and promotes beta-O-4 ether bond cleavage. The use of ammonium chloride in conjunction with enzymatic haloperoxidase-based bleaching could be a route to minimize lignin chlorination.