Effect of an acid treatment on polyphenols and antioxidant activity of sage extracts (Salvia officinalis L.)

Sage (Salvia officinalis L.) is one of the most appreciated natural sources of bioactive compounds, among which polyphenols have attracted more attention due to antioxidative activity. Phenolic compounds sage differ significantly based on chemical structure, therefore different extraction techniques have been applied to obtain polyphenols from sage. The most frequently used methods for extracting phenolic compounds from their plant sources include either solvent extraction or supercritical fluid extraction. Solvent extraction technique (Soxhlet, conventional, microwave and ultrasound assisted extraction) were reported in literature to obtain sage extracts. Even if these techniques are able to provide with bioactive extracts, more environmentally friendly and selective extraction technique are nowadays preferred. The aim of this study was to analyse the effect an acid treatment (10, 20 and 25% HCl in 30% ethanol and aceton) and extraction time (30, 60 min) on extraction yield of polyphenols. The total phenolics and flavonoid content of sage extracts were evaluated using Folin-Ciocalteu method and aluminum chloride (AlCl3) method, respectively. The individual phenolic compounds were quantified using HPLC UV-PDA. In addition, the antioxidant capacity was evaluated by using DPPH (2, 2'-diphenyl-1-picrylhydrazyl) free radical scavenging method. Comparing the solvents used for extraction, the highest extraction yield of tolal phenols and flavonoids was observed using 30% ethanol through 30 minutes. The addition of 10% HCl was influenced the increase extraction capacity of phenolic compounds, while higher percentage of HCl (20 and 25%) negatively affecting the isolation of sage phenolics. The total phenolic content ranged from 3253.33 to 6278.12 mg/100g of dry sage, expressed as rosmarinic acid equivalents. The flavonoid content ranged from 3022.08 to 5649.60 mg/100g of dry sage, expressed as rutin equivalents. The main phenolic compounds determined in sage extract were: rosmarinic acid, folowed by luteolin and apigenin glycosides, and caffeic acid derivates. The antioxidant capacity of obtained extract correlated with concentration od total phenolics and flavonoids, and among individual phenolics the rosmarinic acid contributed the most to the AOC. The best extraction capacity of phenolics from sage was achieved by applying 30% ethanol through 30 minutes, and the addition of acid did not significantly affect the increase the extraction yield of phenols. Application of acid hydrolysis in extraction of sage phenols decreased their amounts, but at the same time increase the amount of aglycones.