The Thyme oil pickering emulsion for the biological cleaning of historical stone surfaces

The Thymus genus is one of the most taxonomically complex genera in the Lamiaceae family and includes 250–350 taxa (species and varieties) of wild growing evergreen species of herbaceous perennials and subshrubs, native to Southern Europe, Africa and Asia. Thyme is a largely used medicinal plant for its expectorant, spasmolytic and antiseptic properties and infusions are employed for treating ulcers, dermatitis and rheumatic pains. The essential oil of Thymus ssp. shows a broad spectrum of bioactivities. In fact, its application as food preservative, as antioxidant, and as additive to enhance organoleptic characteristics has been reported. Thymus capitatus (L.) Hoffmanns. & Link. [syn. Coridothymus capitatus (L.) Reichenb. fil; Thymbra capitata (L.) Cav.; Satureja capitata L.] (Lamiaceae) is a Mediterranean endemic plant commonly used as a condiment for typical Mediterranean cuisine in Portugal, Spain, Italy, Cyprus, and Greece (Facciola, 1990). It is very rich in the terpenes thymol, carvacrol, and p-cymene. Chemotypes thymol, thymol-carvacrol, and carvacrol have been described, the latter being the most abundant (Bounatirou et al., 2007).Several heterotrophic microorganisms (bacteria and fungi) have the ability to interact with historical material such as textile, leather, paper, paintings, wood, papyri. Species of bacteria, fungi and algas can cause deep deteriorations of the items. Also stone monuments, in moderate and humid climates, can be colonized by fungal communities. The surfaces of stone monuments can be altered by fungal activity via hyphal penetration through the porous stone matrix and by production of organic acids and pigments (Stupar et al., 2014). Herein we reports on Maltese accession of Thymus capitatus essential oil as anti-microbial agent against several microorganism, infesting historical stone surfaces.