Antioxidant mechanism of essential oils and their major constituents, and the synergism between them.

The bark of the tree species Myrcia eximia DC., which occurs in secondary forests in the Brazilian Amazon, is described for the first time. The aim was to provide a broad knowledge of its composition, to add value, and to direct uses to the bark of this species based on its polyphenolic content and antioxidant capacity. The bark is formed by conducting phloem, nonconducting phloem, and rhytidome. In addition, dead phloem occurs between the periderms. The average chemical composition of the bark was 45.6% total extractives, 1.4% suberin, 1.7% ash, and 21.1% lignin. The ethanol-water extract had a high content of flavonoids and condensed tannins [300.8 and 877.3 mg catechin equivalents (CE) g−1 of the extract, respectively]. High-performance liquid chromatography (HPLC) was used to quantify the presence of rutin, quercetin, and gallic, ferulic, and o-coumaric acids. The bark extract showed strong 2,2-diphenyl-1-picrylhydrazyl hydrate (DPPH) free radical scavenging activity, which was superior to that of the commercial antioxidant butylated hydroxytoluene (BHT), with an IC50 of 85.2 μg mL−1. Based on these results, it is evident that the bark of M. eximia from the Brazilian Amazon rainforest is a new and potential natural source of phenolic compounds and antioxidants, and its extracts can be used in the food and pharmaceutical industry and in various condensed tannin-based products.

The chemical compositions of the essential oils from the leaves and flowers of Callistemon viminalis and their insecticide and fungitoxic activities were determined. The essential oil was extracted by the hydrodistillation method using a modified Clevenger apparatus. The chemical characterization was performed by GC-MS and GC-FID. The evaluation of the insecticidal activity was performed with the Myzus persicae aphid, and the antifungal potential was determined via the inhibition of the mycelial growth of Alternaria alternata, Fusarium oxysorum and Botrytis cinérea phytopathogenic fungi. The principal components of the essential oils from the leaves and flowers were eucalyptol (84.60% and 61.47%), α-pinene (10.28% and 21.48%) and α-terpineol (2.59% and 2.79%), respectively. The use of a 0.5% concentration of the essential oil from the flowers influenced the preference of aphids and their reproduction. The number of adult aphids decreased within a period of 48 hours in the presence of the essential oil from the leaves. In the test with no chance of choice, the mean number of adults decreased with both oils within 48 hours.

Essential oils can be considered antifungal agents in controlling food contamination, due to their biological potential. Eremanthus erythropappus essential oil (EEO) was extracted by hydrodistillation, and its chemical composition was evaluated by gas chromatography using mass spectrometer (GC‐MS) and flame ionization detectors (GC‐FID). EEO antifungal and antimycotoxygenic effect was evaluated on different species of Aspegillus genus. The main component of the EEO was α‐bisabolol (98.853%). The essential oil exhibited fungicidal activity at concentrations of 0.98, 15.63, and 15.63 μL/mL against Aspergillus carbonarius, Aspergillus flavus, and Aspergillus ochraceus, respectively. The application of the EEO significantly inhibited ochratoxin A production that ranged from 62.06% to 84.27% and from 68.29% to 98.44% for the fungal species A carbonarius and A ochraceus, respectively, and also inhibited the production qualitatively of aflatoxins B1 and B2. Ergosterol biosynthesis of fungi A carbonarius (76.56%‐92.07%), A flavus (81.28%‐97.75%), and A ochraceus (47.61%‐85.56%) significantly decreased in the presence of EEO. Electromicrographs showed morphological alterations and some damages caused by EEO in the fungal membranes of three fungi species. There was a change in the hyphae uniformity present in the fungi and also loss of conidia integrity in A carbonarius, and no conidia formation in A flavus and A ochraceus, after treatment with the essential oil. Therefore, the results suggested that EEO was capable of inhibit fungal growth, ergosterol biosynthesis, and the production of mycotoxins that can contaminate food.

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