Evaluation of Carboxymethyl Cellulase Activity as an Indicator of Active Moulds Inside Foxing Spots on Paper

ABSTRACT Foxing is a special case of fungal deterioration on paper, recognizable by spots of yellowish to brownish colours. Measuring the carboxymethyl cellulase activity (CMCase) by 3,5-dinitrosalicylic method was used to assess the presence of active cellulase inside foxing stains. This was done on foxed paper samples and compared with five fungal strains (belonging to the species Eurotium herbariorum, Talaromyces atroroseus, and Penicillium minioluteum) with cellulolytic capacity, previously identified inside foxing spots, and a highly cellulolytic strain of Trichoderma viride, as a reference. The highest activity of T. viride, expressed as the reducing equivalent glucose released (mg L−1), is achieved at 26°C and in Czapek medium supplemented with carboxymethyl cellulase and sucrose. In the same conditions, for all strains, the activities reached their highest value on the seventh day and then decreased. The method was sufficiently sensitive to indicate the presence of CMCase activity inside foxing spots. These cellulase activities cause paper degradation even after the fungus dies, as the excreted enzymes remain active on the substrate.