Enzymatic degradation of mould stains on paper analysed by colorimetry and DRIFT-IR spectroscopy

Melanin is chemically and by physical characteristics very similar to lignin, a major constituent of wood, and therefore ligninolytic enzymes of white-rot fungi were tested for their ability to selectively degrade melanin. Melanin degradation was studied both in liquid suspensions of melanin and on melaninised paper samples. Liquid suspension samples were tested for changes in their chemical composition (appearance and relative representation of functional groups and chemical bonds) with FTIR spectrometry. Changes in colour of melaninised paper samples were investigated with a colorimeter. Effectiveness of the treatment (bleaching) was determined as a change in lightness (ΔL). Melanin was oxidised in the liquid suspensions, and the intensity of modification varied depending on the procedure employed. The most pronounced changes in melanin were observed in laccase-1-hydroxybenzotriazole (HBT) treatment at heightened air pressure. The most prominent discoloration of the melaninised paper samples (and no visually detectable damage to the integrity of the paper) was, like in the case of the liquid suspensions, observed after laccase-HBT treatment.