Polyphenol composition and antioxidant and metal chelating activities of the solid residues from the essential oil industry
Introduction
Aromatic plants have been widely used from ancient times in medicine, cosmetics and for preserving and improving the flavour of foods. Their beneficial properties have been mainly attributed to the presence of essential oils, which are complex mixtures of compounds belonging to diverse chemical families including terpenes, alcohols, aldehydes, phenolic compounds, esters, ethers and/or ketones. These compounds are well characterized in most of the aromatic plants and numerous publications have been devoted to their antioxidant, antimicrobial, antitumor and bioplaguicide properties (Gould, 1997, Miguel, 2010, Santana et al., 2012).
Essential oils are usually obtained from raw plant materials (flowers, buds, seeds, leaves, twigs, bark, herbs, wood, fruits and roots) by distillation with water and/or steam. The average yield of essential oil distilled from aromatic plants is below 5% (w/w) and consequently a considerable amount of both liquid and solid residues is generated during the industrial processing (Santana-Méridas et al., 2012). These residues may result in environmental concerns if they are not properly managed, but they are also a significant source of bioactive compounds that can increase the overall profitability of the aromatic plants improving the rational utilization of natural resources.
Residues from distillation are especially rich in polyphenols that can be exploited as health-promoting compounds, as antioxidants in food and feed or as anti-aging ingredients in cosmetic products (Navarrete et al., 2011, Torras-Claveria et al., 2007). However, the literature concerning chemical and biological characterization of these residues is scarce especially in the case of solid residues. Torras-Claveria et al. (2007) have detected flavonoids and hydroxycinnamoylquinic acid derivatives with antioxidant activities in lavandin (Lavandula × intermedia Emeric ex Loiseleur) waste and Parejo et al. (2004) have reported the separation and characterization of phenolic compounds in the remaining material after distillation of fennel (Foeniculum vulgare Mill.). More recently, phenolic compounds with antioxidant, antiradical and antiacetylcholinestarase activities have been described in spent flowers and green leaves of oil-bearing rose (Göktürk and Baydar, 2013) and in decoction waters of some aromatics plants (Albano et al., 2012).
Since much of phenolic compounds are not volatile, are not degraded with thermal treatments and remain in the aromatic plants wastes after distillation of raw plant materials (Torras-Claveria et al., 2007). Aerial parts of Cistus ladanifer L. show abundance of hydrolysable tannins derived from gallic and ellagic acids, and flavonoids like quercetin, kaempferol and apigenin derivatives (Barrajón-Catalán et al., 2011, Barros et al., 2013, Chaves et al., 1998, Fernández-Arroyo et al., 2010), whereas Lavandula × intermedia is characterized by the presence of phenolic acids and procyanidins (Blažeković et al., 2010). To our knowledge, the polyphenol composition of aerial parts of Santolina rosmarinifolia L. and Thymus mastichina L. has not been yet investigated. However, Thymus species have been reported as sources of a large variety of phenolic acids and flavonoids, which play important role as antioxidants (Roby et al., 2013) and as taxonomic markers providing distinction of species (Boros et al., 2010, Corticchiato et al., 1995, Marin et al., 2003). Literature on the polyphenol composition of the genus Santolina is very scarce although some flavonoids like apigenin, luteolin and quercetin have been described as components of Santolina oblongifolia Boiss. with anti-inflammatory activity (Silván et al., 1996).
In this work, we have identified the major polyphenols present in solid residues after the steam distillation of C. ladanifer, Lavandula × intermedia, S. rosmarinifolia and T. mastichina, and evaluated their antioxidant and chelating activities by means of several in vitro methods, such as the β-carotene/linoleate model system, reducing power, DPPH radical scavenging, and iron and copper ion chelation. Two methods of extraction have been used: Soxhlet extraction and ultrasound-assisted extraction. The objective is to investigate the potential of such residues as source of antioxidant compounds in order to improve the added value of these aromatic plants.
Section snippets
Standards and reagents
Gallic acid, Folin–Ciocalteu's phenol reagent, linoleic acid, β-carotene, Tween 20, potassium ferricyanide (III), iron (III) chloride, iron (II) chloride tetrahydrate, 2,2-diphenyl-1-picrylhydrazyl (DPPH), ferrozine, pyrocatechol violet (PV) were purchased to Sigma–Aldrich (St. Louis, MO, USA). The phenolic compounds standards, rosmarinic acid, luteolin, catechin and syringic acid were from Fluka-Sigma–Aldrich® (St. Louis, MO, USA), and luteolin-O-glucoside, quercetin, kaempferol,
Extraction methods
Ultrasonic-assisted extraction has gained acceptance as a valuable method to obtain polyphenols from different plant materials because of its simplicity, efficiency of extraction and the lower amount of solvent required in comparison with other extraction procedures (Annegowda et al., 2012, Shirsath et al., 2012). A priori, this method can be considered a more gentle method than other more conventional like Soxhlet due to its lower temperature and shorter time of working, and consequently is
Conclusions
Summarizing, the solid residues from the aromatic plant evaluated constitute a valuable source of polyphenols with significant antioxidant and metal chelating properties. Nevertheless, the yield of extraction, the total content of polyphenols, and the percentage of each individual polyphenol in the extract largely depended on the method of extraction used. The Soxhlet system was more effective than the ultrasonic-assisted extraction in both the yield of extraction and the content in total
Acknowledgments
This work was supported by the grants RTA2012-00057-C03-03 (INIA, Spain). We are grateful to the European Social Fund and to Fundación Parque Científico y Tecnológico de Albacete for additional financing. We thank to European Science Foundation (ESF) through the COST Action FA1101 (http://www.saffronomics.org) for strengthening the existing networks between the teams involved in this work. Our particular thanks to the team of Prof. Polissiou of the Agricultural University of Athens (Greece) for
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