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The influence of microwave assisted extraction on the recovery of phenolic acids and flavone glycosides from sage (Salvia officinalis L.)

Sage (Salvia officinalis L.) is a rich source of structurally different polyphenols, which extraction is influenced with applied extraction technique, raw material related factors, polarity of extraction solvents, solvent to sample ratio, temperature, extraction time, acidity, etc. Therefore, this research was focused to examine the influence of microwave assisted extraction (MAE) on the yield of polyphenols as well as the composition of the obtained extracts. The influence of the solvents (water, 30 % aqueous solution of ethanol and acetone with or without 10% addition of 0.1 M HCl), microwave power (100, 300 and 500 W) and temperature (60 and 80 oC) was observed. Independent of the applied extraction conditions, all extracts contained the same composition of phenolic acids (rosmarinic-RA, vanillic, caffeic, syringic, sagerinic, salvianolic K and salvianolic I acid), methyl rosmarinate, and flavone glycosides (luteolin-3'- glucuronide- L3-Gr, 6-hydroxyluteolin-7-glucoside, luteolin-7-glucuronide, luteolin-7-glucoside, apigenin-7-glucuronide and apigenin-7-glucoside). The predominant phenolic acid was RA (85-90%), and flavone L3-Gr (45-55%). Statistical analysis showed that all extraction parameters had significant influence on the recovery of the phenolic acids and flavone glycosides (p≤0.05). The acid addition was more efficient when binary solvents, such as 30% aqueous ethanol or acetone, were used for the extraction. Furthermore, the highest recovery of all studied groups of polyphenols, as well as individual ones (RA and L3-Gr), was achieved with an acidified 30% aqueous acetone at 80 oC /500 W. This effect is attributed to the combined impact of acid and microwaves, which partially affects better absorption of microwave energy, which affects the temperature increase in the plant cells, damage of the cell walls and better excretion of the polyphenols into the surrounding solvent. This research strongly supports the hypothesis that combined influence of acidified binary solvents and appropriate microwave power contribute to the efficiency extraction of polyphenols from the dried sage leaves.

sage, microwave assisted extraction, phenolic acids, flavone glycosides

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