Essential oils of Portuguese flavouring plants: potential as green biocides in cultural heritage

Microbial biodeterioration is a growing problem in cultural heritage (CH). Many biocides used to control CH biodeterioration have toxic effects and risks of contamination for health and the environment. Essential oils (EOs) due to their antimicrobial potential and low toxicity represent a sustainable and safe alternative in the control of microbial growth in heritage assets. Nevertheless, EOs volatility is one of the main challenges for its use in bio-mitigation adapted to cultural heritage. The encapsulation of EOs may have an alternative strategy for the use of EOs as green biocides that promote a controlled release of EO. In this study, seven EOs of flavouring herbs were screened to evaluate their antimicrobial potential against filamentous fungi, yeast or bacteria strains, previously isolated from colonized artworks. Free EOs, namely L. luisieri and C. nepeta EOs, showed a large antimicrobial spectrum, with high activity for A. niger, Cladosporium spp., Penicillium spp., Rhodotorula sp. and Arthrobacter sp. strains. EO of T. vulgaris shows similar antifungal activity when encapsulated by co-precipitation with β-cyclodextrin, for an encapsulation efficiency higher than 50%. The results suggest the potential use of EO in the safeguard of cultural assets, as eco-friendly, biodegradable and non-toxic biocides, as a green and useful approach when compared to traditional biocides