Antifungal potential of three natural oils and their effects on the thermogravimetric and chromatic behaviors when applied to historical paper and various commercial paper sheets

Three natural extracted oils from Citrus reticulata peels, C. aurantifolia leaves, and Linum usitatissimum (linseeds) were used as antifungal agents against the growth of Aspergillus flavus and Penicillium chrysogenum. The following main compounds (determined via gas chromatography–mass spectrometry) were found. The essential oil (EO) from C. aurantiifolia leaves contained limonene (22.96%), geranyl acetal (13.53%), and geraniol acetate (13.33%); the n-hexane oil from C. reticulata peels contained methyl-13-cyclopentyltridecanoate (16.74%), and D-limonene (16.06%); and linseed oil contained linoleic acid (27.36%), and oleic acid (19.01%). The inhibition of fungal growth significantly was reached 100% against A. flavus at all tested C. aurantifolia leaf EO concentrations and at a concentration of 2000 µL/mL for linseeds oil. The growth inhibition reached 100% against P. chrysogenum with C. aurantifolia leaf EO concentrations of 125-2000 µL/mL. Citrus reticulata peel EO had 100% growth inhibition of P. chrysogenum at concentrations of 2000 µL/mL and 1000 µL/mL, while linseeds oil had 100% growth inhibition at 2000 µL/mL. Thermogravimetric analysis showed that C. aurantifolia EO yielded the greatest thermal stability and color change protection to cotton pulp, while linseed oil was found to protect wood pulp-based and historical papers.