Analysis of volatile constituents from post-harvesting handling and optimization of extractive solvent on the quality of the leaves of Premna serratifolia L.

Abstract

The objective of this study was to compare the chemical composition of volatile oils, phenolic content and antioxidant activity of the fresh, dried, and fermented leaves of Premna serratifolia, and to find a suitable extractive solvent to prepare a good quality extract from its leaves. Volatile oils from the fresh, dried and fermented leaves were analyzed by gas chromatography–mass spectrometry. The phenolic content and antioxidant activity were determined by DPPH and Folin-Ciocalteu methods. A total of 77, 82 and 90 compounds were detected in the fresh, dried and fermented leaf volatile oils, respectively. The main compounds of the fresh leaf volatile oils were amyl vinyl carbinol (15.8–32.6%), linalool (11.1–15.1%), phytol (7.7–12.5%), salicylic acid methyl ester (3.9–7.2%) and (E)-caryophyllene (3.1–6.6%). After drying and fermentation, amyl vinyl carbinol was decreased to 6.3–13.8% and 6.9–11.5%, respectively. Likewise, linalool and phytol decreased to 6.3–7.5% and 7.3–9.0% after drying, and decreased to 5.3–7.9% and 2.0–3.4% after fermentation. After drying, (E)-caryophyllene increased significantly to 6.6–12.2%, becoming the most prevalent compound, and palmitic acid ethyl ester (1.17%) dramatically hydrolysed to palmitic acid (5.0%). The fermentation method resulted in a significant increase in phenolic compounds, particularly p-vinylanisole (2.4–41.1%), which became the predominant compound, as well as a significant decrease in phytol and the finding of acorenone B (4.4%) as a new compound. Among the 80% ethanolic extracts of fresh, dried and fermented leaves, fresh leaf extract possessed the highest phenolic content of 6.08%GAE and 67.24% of antioxidant activity at the concentration of 100 µg/mL. Premnaodoroside A and the mixture of glucose and fructose were isolated from the dried leaves. A TLC-densitometric method was developed using premnaodoroside A as a standard marker. The method demonstrated satisfactory specificity, precision and accuracy with good linearity (R2 > 0.99) in the range of 0.11-0.87 µg/spot, with a limit of quantitation and a limit of detection of 0.04 and 0.13 µg/spot, respectively. The analysis of 0, 20, 40, 60, 80 and 100% ethanolic extracts of three samples revealed that 100% ethanolic extract exhibited the highest content of premnaodoroside A (3.23–5.25%), total phenolic content (7.56-8.24% GAE) and antioxidants (4.92–6.66% AAE), but its extractive yields (13.57-19.57%) were the lowest. On the contrary, solvents with a lower percent of ethanol gave a higher percent of extractive yield. 80% Ethanol gave the optimization of both the yield of the extract and the content of the interesting compounds.

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