Centauries as underestimated food additives: Antioxidant and antimicrobial potential

Highlights

• Centauries are an appreciative source of biologically active compounds.

• Phenolics, flavonoids, xanthones and secoiridoid glycosides were quantified.

• Considerable antioxidant activities and ferric reducing capacity was recorded.

• Appreciative antibacterial and strong antifungal activities were demonstrated.

• Centauries could be recommended as food preservation additives.

Abstract

Methanol extracts of aerial parts and roots of five centaury species (Centaurium erythraea, C. tenuiflorum, C. littorale ssp. uliginosum, C. pulchellum, and Schenkia spicata) were analysed for their main secondary metabolites: secoiridoid glycosides, a group of monoterpenoid compounds, and phenolics (xanthones and flavonoids), and further investigated for antioxidant capacity and antimicrobial activity. The results of ABTS, DPPH, and FRAP assays showed that above ground parts generally displayed up to 13 times higher antioxidant activity compared to roots, which should be related to higher phenolics content, especially flavonoids, in green plant organs. Secoiridoid glycosides showed no antioxidant activity. All the tested extracts demonstrated appreciative antibacterial (0.05–0.5 mg ml⁻¹) and strong antifungal activity (0.1–0.6 mg ml⁻¹). Our results imply that above ground parts of all centaury species studied, could be recommended for human usage as a rich source of natural antioxidants and also in food industry as strong antimicrobial agents for food preservation.

Introduction

The protection of human body against oxidative stress and/or pathogenic bacteria and fungi relies not only on endogenous defense mechanisms, but also on exogenous compounds taken in food and beverages. Many naturally occurring compounds found in edible and medicinal plants and spices have been shown to possess strong antioxidant (Gülçin, 2012) and antimicrobial activity (Tajkarimi, Ibrahim, & Cliver, 2010) and could serve as a natural source of bioactive molecules which significantly support the defense against various diseases and disorders.

European centauries (genera Centaurium and Schenkia, fam. Gentianaceae) are of great importance for food and beverage bittering, and have been widely used since ancient times. Centauries, especially Centaurium erythraea, are popular constituents of many modern gastric herbal preparations and dietary supplements (e.g. Botion, Ferreira, Côrtes, Lemos, & Braga, 2005). This species is listed in the Council of Europe (EMA, 2009) as a natural source of food flavoring, in category N2 (Newall, Anderson, & Phillipson, 1996), which could be added to food stuffs in small quantities (0.0002–0.0008%). Other species investigated in this study are often referred as a substitute for C. erythraea in “Centaurii herba” drug (Bisset, 1994). Numerous pharmacological effects have been attributed to centauries, including stomachic, digestive, antiinflammatory and antipyretic effects (Berkan et al., 1991, Newall et al., 1996), cholagogue, hepatoprotective, gastroprotective (Tuluce, Ozkol, Koyuncu, & Ine, 2011), diuretic (Haloui, Louedec, Michel, & Lyoussi, 2000), wound-healing, antimicrobial (Ross et al., 2011, Šiler et al., 2010), and antioxidant activities (Shahat et al., 2003, Valentão et al., 2001).

Phytochemical studies of centauries revealed the presence of secoiridoid glycosides (SGs) (C-10 monoterpenoids, which are built of isoprenoid units), and phenolics (xanthones, phenolic acids and their derivatives) as main constituents (Beerhues and Berger, 1995, Bibi et al., 2006, Valentão et al., 2002, van der Sluis, 1985). The most abundant SGs (swertiamarin (SM), gentiopicrin (GP), and sweroside (SW)) (Fig. 1) show a vast spectrum of biological activities, such as fungitoxic, antibacterial (Šiler et al., 2010), gastroprotective (Niiho et al., 2006), hepatoprotective (Kondo, Takano, & Hojo, 1994), sedative (Bhattacharya, Reddy, Ghosal, Singh, & Sharma, 1976), and antitumor (Ishiguro et al., 1988). There are many forms of xanthones (basic skeleton C6–C1–C6) isolated from centauries, including eustomin, demethyleustomin, decussatin, and methylbellidifolin (Fig. 1) (Beerhues and Berger, 1995, Jensen and Schripsema, 2002, Krstić et al., 2003), and they also show a wide range of biological activities (Ross et al., 2011). Some flavonoids (basic skeleton C6–C3–C6) isolated from centaury species are reported to possess antioxidant potential (Shahat et al., 2003).

This work was aimed at investigating the antioxidant potential and antimicrobial activity of five centaury species: C. erythraea Rafn, C. tenuiflorum (Hoffmans. & Link) Fritsch, C. littorale (Turner) Gilmour ssp. uliginosum (Waldst. & Kit.) Melderis, C. pulchellum (Sw.) Druce, and Schenkia spicata (L.) Mansion, and to correlate the observed biological activities with the main constituents content detected in methanol extracts of their above ground parts and roots. One more objective was to re-evaluate the potential of centauries for implementation in food industry, since their role as food additives has been neglected in last decades.