Optimization of the extraction process of polyphenols from Thymus serpyllum L. herb using maceration, heat- and ultrasound-assisted techniques

Abstract

Despite the fact that Thymus serpyllum is well-known medicinal plant and its chemical profile and biological activity have been investigated, there is no detailed study regarding the influence of different techniques and conditions on the extraction of polyphenolic compounds from Serpylli herba. The aim of this study was optimization of the extraction parameters that improves the efficiency of polyphenols extraction from T. serpyllum: particle size, solid-to-solvent ratio, solvent type and extraction time, by using maceration, heat-and ultrasound-assisted extraction (HAE and UAE). The extraction efficiency was expressed via total polyphenol content (TPC) and total flavonoid content (TFC). The statistical analysis (one-way ANOVA and full factorial design) has revealed that the optimal conditions for achieving the best polyphenols yield were particle size of 0.3 mm, 1:30 solid-to-solvent ratio and 50% ethanol, as environmentally friendly extraction medium, while extraction time has not shown statistically significant influence on polyphenols concentration, in all procedures. Under these conditions, the measured TPC was 26.6 mg GAE/L in maceration, 29.8 mg GAE/L in HAE and 32.7 mg GAE/L in UAE, which was in agreement with the predicted values, while TFC was 14.3 mg CE/L, 12.4 mg CE/L and 16.7 mg CE/L for maceration, HAE and UAE, respectively. According to total polyphenols yield, the efficiency of the extraction methods for all variables was ranked by significance in the following order: UAE > HAE > maceration, whereas total flavonoids yield was the highest in UAE, although there was no statistically significant difference between maceration and HAE. According to our results, UAE could be selected as the most successful and suitable technique for extraction of bioactive polyphenolic compounds from Serpylli herba. Using LC/MS and HPLC analysis, 9 polyphenolic compounds were identified and quantified: 6,8-Di-C-glucosylapigenin, chlorogenic acid, 6-hydroxyluteolin 7-O-glucoside, caffeic acid, luteolin 7-O-glucuronide, apigenin glucuronide, salvianolic acid K isomer, rosmarinic acid and salvianolic acid I. This study was an initial step in production of polyphenols-rich wild thyme extracts aimed to be used for formulation of foodstuffs and medicines.

Polyphenols extraction from plant sources

“…Maceration strongly depends on the properties of plant material, particularly particle size, thus the internal diffusion may be the limiting step during extraction (Wang and Weller, 2006). According to the literature, the highest polyphenols yield from Aronia melanocarpa and Thymus serpyllum is achieved with the smallest particles, because of the increased active surface area and the enhanced contact of matrix with solvent (Ćujic et al, 2016;Jovanović et al, 2017). The choice of solvent depends on physical and chemical properties of target compounds, as well as on applied extraction procedure (Wang and Weller, 2006).…”

“…Water, ethanol, methanol and their mixture are the most commonly applied solvents for polyphenols extraction (Aziz and Habib-Ur-Rehman, 2008;Ćujic et al, 2016;Vajić et al, 2015). According to the recent studies, polyphenols from aromatic plants are preferentially extracted with mixture of alcohol and water using maceration, particularly when they are in a glycoside form (Costa et al, 2012;Jovanović et al, 2017;Vajić et al, 2015). In a mixture, one solvent can enhance the solubility of the polyphenols, while the other can improve desorption (Mustafa and Turner, 2011).…”

“…According to Fick's second law of diffusion, by prolongation of the extraction time, the polyphenols yield is increased . However, in the polyphenols extraction from A. melanocarpa, T. serpyllum, Urtica dioica and Lawsonia inermis at room temperature, the extraction time did not have statistically significant influence on polyphenols yield (Uma et al, 2010;Ćujic et al, 2016;Jovanović et al, 2017;Vajić et al, 2015). The reason could be in occurrence of two stages in maceration: an initial increase of the polyphenols content in the beginning of the process, followed by slow extraction (Vuleta et al, 2012).…”

“…The main disadvantages of maceration include (1) long extraction time, (2) a large quantity of solvent, and (3) lower polyphenols yield. Maceration is widely and successfully applied procedure for extraction of thermosensitive polyphenols compounds from different plant sources (Ćujic et al, 2016;Jovanović et al, 2017;Vajić et al, 2015). Nevertheless, in comparison to novel extraction methods, maceration is old-fashion and time-consuming extraction procedure, which does not provide high polyphenols yield (Jovanović et al, 2017).…”

“…According to the literature, the polarity of solvent decreases by applying high temperature during the extraction, which makes water and ethanol suitable solvents to extract polar, moderately polar and non-polar organic constituents (Mustafa and Turner, 2011). Due to very low polyphenols yield proven in several previous studies, mono-solvent system is not recommended as an appropriate solvent for polyphenols extraction at high temperature (Chizzola et al, 2008;Jovanović et al, 2017;Miron et al, 2011). Several studies have revealed that solid/solvent ratio and temperature had significant influence on polyphenols yield and with the increase of ratio the polyphenols content in extracts also increases (Bucić-Kojić et al, 2007;Jovanović et al, 2017;Pompeu et al, 2009).…”