Essential Oils of Plants as Biocides Against Microorganisms Isolated from Portuguese Convent of Christ in Tomar

Abstract

Biodeterioration observed in art and architectural works holding patrimonial value is primarily due to the proliferation of various microorganisms, that through their energy-producing metabolisms lead to the formation of biotic substances that can attack the physicochemical structures of artworks’ constitutive materials. In conservation-restoration, different biocides of synthetic origin which exhibit some human and environmental toxicity are traditionally used. Natural resources exploitation awareness and side effects of common disinfectants and inhibitors led to the need for natural compounds with biocidal effects. This work aimed to evaluate the possible use of essential oils (EOs) extracted from endogenous plants as novel conservation products against the biocolonization of cultural heritage materials. The biocidal potential of five EOs extracted from the indigenous plants Thymus mastichina (Tm), Helichrysum stoechas (Hs), Mentha pulegium (Mp), Foeniculum vulgare (Fv) and Lavandula viridis (Lv) were evaluated. Microorganisms collected at an emblematic site of the country's cultural heritage, Convent of Christ in Tomar, were used to evaluate the biocidal activity of the EOs at concentrations of 2, 10 and 20% (v/v), emulsified in water with 0.2% SDS (m/v). For the tested conditions and comparatively to the commercial biocide Biotin T (1% v/v), it can be concluded that: (i) Hs didn’t exhibit fungicidal nor bactericidal activity; (ii) Tm exhibited only bactericidal activity; (iii) in contrast, the other EOs exhibited both fungicidal and bactericidal activity. The results allow considering the use of Tm, Mp, Fv and Lv EOs as a valid alternative to commercial biocides, providing a prospective of application in the field of green conservation of Cultural Heritage.