Diallyl Trisulfide, the Antifungal Component of Garlic Essential Oil and the Bioactivity of Its Nanoemulsions Formed by Spontaneous Emulsification.

The aim of this study was to evaluate the chemical compounds of garlic essential oil (EO), and determine the antifungal efficacy of garlic EO and its major components, diallyl trisulfide and its nanoemulsions against wood-rotting fungi, Trametes hirsuta and Laetiporus sulphureus. GC-MS analysis revealed that the major constituents of garlic EO were diallyl trisulfide (39.79%), diallyl disulfide (32.91%), and diallyl sulfide (7.02%). In antifungal activity, the IC50 value of garlic EO against T. hirsuta and L. sulphureus were 137.3 and 44.6 µg/mL, respectively. Results from the antifungal tests demonstrated that the three major constituents were shown to have good antifungal activity, in which, diallyl trisulfide was the most effective against T. hirsuta and L. sulphureus, with the IC50 values of 56.1 and 31.6 µg/mL, respectively. The diallyl trisulfide nanoemulsions showed high antifungal efficacy against the examined wood-rotting fungi, and as the amount of diallyl trisulfide in the lipid phase increases, the antifungal efficacy of the nanoemulsions increases. These results showed that the nanoemulsions and normal emulsion of diallyl trisulfide have potential to develop into a natural wood preservative.

Cu2+-assisted laccase from Trametes versicolor enhanced self-polyreaction of triclosan.

Laccase-mediated humification processes (L-MHPs) can be used to polymerize and transform phenolic pollutants in water. However, the mechanism on Cu2+ impacts the self-polymerization of multi-purpose antimicrobial agent triclosan during L-MHPs is less understood. Here, the influence of divalent metal ions (DMIs) on Trametes versicolor laccase activity was investigated. Particularly, the performance of Cu2+-assisted laccase in polymerizing and transforming triclosan was systematically characterized. Compared with DMI-free, the activity of laccase was obviously accelerated with Cu2+ present due to copper is a vital component of laccase catalytic center. It was found that Cu2+-assisted laccase was effective in transforming triclosan, and the enzymatic reaction kinetic constants increased from 0.28 to 0.73 h-1 as the Cu2+ concentration increased (0-3.0 mM). Identification of intermediate products revealed that laccase oxidation predominantly generated triclosan dimers, trimers, and tetramers. The presence of Cu2+ reinforced self-polymerization of triclosan via forming more triclosan oligomers relative to the Cu2+-free, which likely attributed to the enhancement of laccase activity and stability with Cu2+ present in L-MHPs. A possible transformation mechanism was proposed as follows: Laccase initially catalyzed the oxidation of triclosan to generate phenoxy radical intermediates, which self-coupled to each other subsequently by radical-mediated CC and COC covalent binding, forming oligomers and polymers. The growth inhibitory assays of freshwater microalgae (Chlamydomonas reinhardtii and Scenedesmus obliquus) demonstrated that the self-polymerized triclosan by L-MHPs had lower toxicity than the parent compound. These findings implied that Cu2+-assisted laccase was an effective strategy for rapidly self-polyreaction and detoxication of triclosan from Cu2+-triclosan combined polluted wastewater.