Essential Oils as Alternative Biocides for the Preservation of Waterlogged Archaeological Wood

Spray Coating of Wood with Nanoparticles from Lignin and Polylactic Glycolic Acid Loaded with Thyme Essential Oils

Ensuring the longevity of wooden constructions depends heavily on the preservation process. However, several traditional preservation methods involving fossil-based compounds have become outdated because they pose a significant risk to the environment and to human health. Therefore, the use of bio-based and bioactive solutions, such as essential oils, has emerged as a more sustainable alternative in protecting wood from biotic attacks. The entrapment of essential oils in polymeric carrier matrices provides protection against oxidation and subsequent degradation or rapid evaporation, which implies the loss of their biocidal effect. In this work, lignin as well as PLGA nanoparticles containing the essential oils from two different thyme species (Thymus capitatus and T. vulgaris) were applied on beech wood samples using spray coating. The prepared coatings were investigated using FTIR imaging, SEM, as well as LSM analysis. Release experiments were conducted to investigate the release behavior of the essential oils from their respective lignin and PLGA carrier materials. The study found that lignin nanoparticles were more effective at trapping and retaining essential oils than PLGA nanoparticles, despite having larger average particle diameters and a more uneven particle size distribution. An analysis of the lignin coatings showed that they formed a uniform layer that covered most of the surface pores. PLGA nanoparticles formed a film-like layer on the cell walls, and after leaching, larger areas of native wood were evident on the wood samples treated with PLGA NPs compared to the ones coated with lignin NPs. The loading capacity and efficiency varied with the type of essential oil, while the release behaviors were similar between the two essential oil types applied in this study.

Essential Oils for the Conservation of Paper Items

Archival documents and artworks stored in libraries frequently undergo degradative processes promoted by the so-called "biodeteriogens" that inhabit these places. A renewed interest in plant-derived products has arisen in those research groups focusing on cultural heritage preservation and looking for new and safe disinfection techniques. In this view, essential oils (EOs) and their volatile organic constituents are very appealing thanks to their versatility of action. A literature survey of the scientific publications involving EOs and/or their major constituents related to the conservation of paper items of cultural heritage interest is presented here, aiming to reveal benefits and limitations of such peculiar plant-derived compounds.

Plant Extracts as Antimicrobial Agents in Sustainable Conservation of Erythrina caffra (Fabaceae) Historical Trees

Microbial colonization plays a relevant role in the biodegradation and biodeterioration of cultural and natural heritage, representing a revealing problem in conservation strategy. In this study, the essential oil (EO) and hydro-alcoholic extract (HAE) of Origanum vulgare L. (Lamiaceae), an aromatic perennial plant, representative of the Mediterranean basin, growing spontaneously and cultivated all over the world, were analysed. Natural products, such as essential oil and hydro-alcoholic extract, have strong antiseptic and antimicrobial properties and are ad hoc applied for the sustainable conservation of Erithryna caffra (Fabaceae). The main taxa revealed in the damaging of these arboreal heritage, are Bacillus sp., Streptomyces sp. and Terribacillus sp. (as bacteria), Alternaria sp., Aspergillus sp. and Chaetomium sp. (as fungi). GS-MS analysis identified carvacrol, thymol and their biosynthetic precursors γ-terpinene and p-cymene, as main components, and the antimicrobial efficiency assayed by in vitro methods (Agar Dish Diffusion, Well Plate Diffusion). In this study, by combining the application/exposure of both HAE and EO, the bacterial and fungal colonies development has been in vitro countered. The results confirm the possible use of plant products as a valid alternative to the traditional synthetic chemical biocides, with full respect to the environment.

Lignin Nanoparticles with Entrapped Thymus spp. Essential Oils for the Control of Wood-Rot Fungi

After decades of utilization of fossil-based and environmentally hazardous compounds for wood preservation against fungal attack, there is a strong need to substitute those compounds with bio-based bioactive solutions, such as essential oils. In this work, lignin nanoparticles containing four essential oils from thyme species (Thymus capitatus, Coridothymus capitatus, T. vulgaris, and T. vulgaris Demeter) were applied as biocides in in vitro experiments to test their anti-fungal effect against two white-rot fungi (Trametes versicolor and Pleurotus ostreatus) and two brown-rot fungi (Poria monticola and Gloeophyllum trabeum). Entrapment of essential oils provided a delayed release over a time frame of 7 days from the lignin carrier matrix and resulted in lower minimum inhibitory concentrations of the essential oils against the brown-rot fungi (0.30-0.60 mg/mL), while for the white-rot fungi, identical concentrations were determined compared with free essential oils (0.05-0.30 mg/mL). Fourier Transform infrared (FTIR) spectroscopy was used to assess the fungal cell wall changes in the presence of essential oils in the growth medium. The results regarding brown-rot fungi present a promising approach for a more effective and sustainable utilization of essential oils against this class of wood-rot fungi. In the case of white-rot fungi, lignin nanoparticles, as essential oils delivery vehicles, still need optimization in their efficacy.

The combined effect of essential oils on wood physico-chemical properties and their antiadhesive activity against mold fungi: application of mixture design methodology

In the heritage field, the microbial adhesion on wood, and consequently the formation of biofilm led to inestimable losses of historical and cultural monuments. Thereby, this study aimed to examine the combined effect of Thymus vulgaris, Myrtus communis, and Mentha pulegium essential oils on wood surface physico-chemical properties, and to elaborate the optimal mixture using the mixture design approach coupled to the contact angle method. It was found that both wood hydrophobicity and electron donor character increased significantly after treatment using an optimal mixture containing 57% and 43% of M. pulegium and M. communis essential oils, respectively. The theoretical and experimental fungal adhesion on untreated and treated wood were also investigated. The results showed that the adhesion was favorable on untreated wood and reduced using the optimal mixture. Moreover, the experimental data demonstrated that the same mixture exhibited an antiadhesive efficacy effect with a reduction of 36-75% in adhesion.

Cyclodepsipeptides: Isolation from Endophytic Fungi of Sarcophyton ehrenbergi and Verification of Their Larvicidal Activity via In-Vitro and In-Silico Studies

Culex pipiens mosquitoes are vectors to many viruses and can transmit diseases such as filariasis and avian malaria. The present study evaluated the larvicidal activity of marine-derived endophytic fungi Aspergillus nomius and Aspergillus flavus from the soft coral Sarcophyton ehrenbergi along with two known cyclodepsipeptide compounds, scopularide A (1) and B (2), isolated from A. flavus extract, against third-instar larvae of C. pipiens, using distilled water as a negative control and toosenedanin as a positive control. The structures of the isolated compounds were confirmed by various spectroscopic analyses. The lethal concentrations (LC₅₀ and LC₉₀) were calculated by probit analysis. Scopularide A was the most potent after 96 h treatment, with LC₅₀ and LC₉₀ values of 58.96 and 994.31 ppm, respectively, and with 82.66% mortality at a concentration of 300 ppm. To unravel the biochemical mechanism of the tested extracts and compounds, their effects against protease, chitinase, phenoloxidases and lipase enzymes from the whole-body tissue of C. pipiens were evaluated after 72 h treatment at LC₅₀ dose. Superior activity was observed for A. flavus extract against all tested enzymes. A molecular docking study was conducted for scopularide A and B on the four tested enzymes, to further verify the observed activity. Results revealed good binding affinities for both compounds as compared to the docked ligands, mainly via a number of hydrogen bonds. This was the first study to report the isolation of endophytic fungi A. flavus and A. nomius from the marine soft coral S. ehrenbergi. The endophytic fungal extract of A. flavus was found to be a promising source for a natural larvicidal agent against C. pipiens populations.