Effect of acidic and enzymatic pretreatment on the analysis of mountain tea (Sideritis spp.) volatiles via distillation and ultrasound-assisted extraction

A number of beneficial medicinal properties are attributed to the extract and essential oil of the aerial parts of Sideritis species (Lamiaceae). Hydrodistillation of the aerial parts of wild Sideritis clandestina ssp. peloponnesiaca (an endemic taxon in northern Peloponnesus, Greece) gave a low essential oil yield (<0.12%); about 65 components, mainly α-pinene, β-caryophyllene, β-pinene, globulol, caryophyllene oxide, were identified via GC–MS. Internal and external standards were used for quantification. For miniaturization of the procedure, we studied side-by-side maceration (MAC) and ultrasound-assisted extraction (UAE) methods, as well as the effect of preincubation in acidic medium (pH 4.8) for 75 min at 37 °C with or without a mixture of cellulase, hemicellulase and pectinase. Maceration and UAE provide consistent chemoprofiling of the main volatile compounds (about 20); UAE has lower demands on time, solvent, plant material (3 g) and results in higher yields. Pretreatment with enzymes can increase the respective yields of hydrodistillation and UAE, but this effect is definitely attributed to the concurrent acidic pretreatment. In conclusion, incubation of plant material prior to hydrodistillation or UAE in citrate buffer, pH 4.8, significantly enhances the overall yield and number of components obtained and is recommended for the analysis of Sideritis volatiles. The acidic pre-treatment method was also successfully applied to analysis of cultivated Sideritis raeseri Boiss. & Heldr. in Boiss. ssp. raeseri; α-pinene, α- and γ-terpinene and β-thujene were predominant albeit in different percentages in flowers and leaves.