Abstract
Camellia japonica is one of the most economically valuable species that can be taxonomically placed in the Theaceae family. Many horticultural varieties of C. japonica have been cultivated as ornamental trees worldwide, owing to their charming flowers. However, young C. japonica flowers usually drop in a “decapitated” form during the peak flowering stage, causing a resource waste. In this study, Essential Oils from the Dropped C. japonica Flowers (EODCJF) were extracted with hydrodistillation and process was optimized by response surface methodology. The chemical profile and antibacterial activity were tested by gas chromatography-mass spectrometry and by disc diffusion, respectively. The optimal extraction parameters were: Immersion time of 9 h, extraction time of 8 h and liquid-to-solid ratio of 39: 1 (mL/g), under these conditions, the yield was 3.20%. The actual yield was in compliance with the predicted result with an error margin of 3.61%. Thirty-three volatile compounds accounting for 94.46% were authenticated in EODCJF with alkanes of 53.96% and alcohols of 28.59%, respectively. EODCJF exerted certain antibacterial capacities against Staphylococcus aureus, Escherichia coli, Bacillus subtilis and Bacillus pumilus. Their antibacterial activities could be contributed by the long-chain alcohols in EODCJF and alkanes may potentiate the dispersion of these liposoluble alcohols in EODCJF.
Highlights
Essential Oils (EOs) are a kind of secondary metabolites in plants
To 3, we can observe that prolonged pre-immersion and extraction time as well as overlarge liquid-tosolid ratio lead to a sharp decline in EODCJF yield. These unexpected phenomena could be explained by the following reasons: (1) pre-immersion of plant materials is beneficial for the dispersion of essential oils in water, thereby increasing extraction yield, overtime immersion before extraction would cause the loss of volatile compounds, leading to a decrease in extraction yield (Hui et al, 2015); (2) long-term hydrodistillation at water boiling temperature would alter the chemical compositions of essential oils and make certain substances that are vulnerable to heating degrade, causing a decline in extraction yield (Zheljazkov et al, 2014); (3) larger amount of water could result in an excessive swelling of raw materials to absorb some substances in EODCJF, leading to a decrease in extraction yield (Xiao et al, 2008)
Under the predicted optimal extraction conditions, the actual yield of EODCJF was almostly equivalent to the predicted yield, and the error margin was smaller than ±5%, indicating that Response Surface Methodology (RSM) coupled with Box-Behnken Design (BBD) could be a feasible way to optimize the extraction parameters of EODCJF
Summary
Essential Oils (EOs) are a kind of secondary metabolites in plants. They usually comprise diverse components that bear smaller molecular weights and aromatic odors (Zhang et al, 2018a). C. japonica is one of the most economically valuable species. Many horticultural varieties of C. japonica have been developed as ornamental trees worldwide, due to the beautiful and charming flowers (Kim et al, 2019; Páscoa et al, 2019). The ethanol extract from flowers of C. japonica exerts antioxidant capacity via scavenging excessive free radicals and reactive oxygen species and via elevating activities of antioxidases (Piao et al, 2011). The quercetin glycosides, gallic acid and its glucoside conjugates isolated from the hot water extract of C
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