Effects of trapped-into-solids volatile organic compounds on paper biodeteriogens

Paper items from historical archives and libraries are frequently colonized by biodeteriogens, the management of which is a major concern. Essential oil Volatile Organic Compounds (VOCs) of thymol, carvacrol and eugenol, with high levels of antimicrobial and insect repellent activity, were stabilized within crystalline networks of beta-cyclodextrins and phenazine-based cocrystals, as a new tool for the control of paper-degrading agents. These formulations were obtained via solvent-free methodologies and resulted as easy handling powders, suitable for the treatment of paper items by indirect contact. Their antimicrobial activity was evaluated on the following species isolated from a book depository at Forte Belvedere (Florence, IT): Alternaria alternata, Aspergillus sp., Cladosporium sp., Trichoderma orientale, Metschnikowia sp., and Bacillus sp. Both formulates displayed a significant antimicrobial activity in vitro, with cocrystals showing higher efficacy than beta-cyclodextrins. The formulates were also tested against the pest Lasioderma serricorne, towards which the cocrystals entrapping carvacrol and thymol exhibited repellent activity. Overall, the phenazine-carvacrol cocrystal was the best-performing formulate, also giving favourable outcomes in terms of antifungal activity in an on-paper in vitro experiment designed to reproduce on a small-scale the critical conditions of an infested archive. These promising results pave the way towards further experimentations of VOC-based solid formulates, to shed light on such products applicability for the preservation of paper items.