Biorefining of goldenrod (Solidago virgaurea L.) leaves by supercritical fluid and pressurized liquid extraction and evaluation of antioxidant properties and main phytochemicals in the fractions and plant material

Highlights

• Solidago virgaurea leaves were biorefined using high pressure extraction methods.

• Lipophilic fraction was separated by supercritical fluid extraction with CO₂.

• Higher polarity compounds were extracted by pressurized liquid extractions.

• Antioxidant potential of extracts and solids was evaluated by the in vitro assays.

• Phytochemicals in leaf fractions identified and quantified by UPLC–MS/MS.

Abstract

Supercritical carbon dioxide (SFE–CO₂) and pressurized liquid extraction (PLE) with increasing polarity solvents were applied for biorefining goldenrod (Solidago virgaurea) into fractions. Extract yields varied from 2.40 to 28.9% (dry weight); the total yields were 42.87–63.79%. The highest content of phenolics and trolox equivalent antioxidant capacity was obtained using PLE at 140 °C, while the highest oxygen radical absorbance capacity (ORAC) value was obtained using the combination of SFE-CO₂/PLE. Antioxidant activity indicators of solid plant substances gradually decreased during extraction as measured by QUENCHER method. α-Tocopherol was the major tocol in lipophilic extracts (61.4–134 µg/g). Ten phytochemicals were quantified: the concentration of quercitrin was 50.7–94.1 mg/g followed by hyperoside, 33.8–70.1 mg/g dry extract weight. PLE fractions increased the oxidative stability of rapeseed oil and emulsion in Oxipres and Rancimat assays. Multistep SFE-CO₂/PLE processes were demonstrated to be effective for producing high added value functional ingredients from goldenrod leaves.

Introduction

Botanicals biosynthesize thousands of secondary metabolism products, among them valuable phytochemicals possessing antioxidant, antimicrobial and other health beneficial properties. Therefore medicinal and aromatic plants have been used in health care, foods and cosmetics since ancient times. Moreover, the importance of botanicals has remarkably increased during the last two decades due to a rapid development of functional foods and nutraceuticals, which have become a major trend in food science and technology as well as in nutrition and disease prevention. So far as many botanical species remain underinvestigated their evaluation is of great interest in terms of discovering new sources of functional ingredients for foods, nutraceuticals, cosmeceuticals, medicines and other applications.

Goldenrod (Solidago virgaurea L.) is a member of the genus Solidago (family Asteraceae), which includes about 120 herbaceous species of North American wildflowers and more than a dozen species inhabiting South America, Europe and Asia. They are common along the edges of moist forests, roadsides and meadows (Kołodziej, 2009). S. virgaurea has been traditionally used to treat inflammations of the urinary tract. Several studies demonstrated that goldenrod leaves, stems and flowers possess antioxidant, antimicrobial, antibacterial, antifungal, anti-inflammatory, antihypertensive, antitumor, anti-adipogenetic, cardioprotective, spasmolytic and diuretic effects (Apáti et al., 2003, Gross et al., 2002, Thiem and Goslinska, 2002, Vonkruedener et al., 1995, Goulart et al., 2007, Anzlovar and Koce, 2014, Demir et al., 2009, Deng et al., 2015, El-Tantawy, 2014, Jang et al., 2016, Laurençon et al., 2013, Starks et al., 2010, Wang et al., 2011). Such effects may depend on various factors. For instance, alcoholic extract of S. virgaurea herb demonstrated slightly stronger antibacterial properties compared with lipophilic hexane extract; however, the latter exhibited antimutagenic activity, which was not found for alcoholic extract (Kołodziej, Kowalski, & Kedzia, 2011). Goldenrod leaf and stem powder demonstrated antioxidant activity in raw ground pork (Kim et al., 2013) and was applied as a dietary fibre in sausages to improve their quality characteristics (Choe et al., 2011). Antimicrobial, sedative, cytotoxic and hypotensive effects were also reported for the essential oils of Solidago species (Chanotiya and Yadav, 2008, Huang et al., 2012, Kołodziej et al., 2011, Mishra et al., 2011).

Various (poly)phenols were identified in goldenrod herb previously, namely caffeic, caffeoylquinic, chlorogenic, gallic and rosmarinic acids; cinnamic acid hydroxyl derivatives, afzelin, astragalin, hyperoside, isorhamnetin, isoquercitrin, kaemferol, kaempferol-3-O-robinobioside, leiocarposide, narcissin, nicotiflorin, quercitrin, quercetin and rutin (Apáti et al., 2002, Apáti et al., 2003, Bader et al., 1998, Condrat et al., 2009, Condrat et al., 2010, Jaiswal et al., 2011, Kristó et al., 2002, Nugroho et al., 2009, Papp et al., 2004, Pietta et al., 1991, Radušienė et al., 2015, Rosłon et al., 2014).

However, the above-cited studies used mainly methanol and hydroalcoholic solvents for the extraction of goldenrod phytoconstituents and in most cases for analytical purposes. Previously applied conventional extraction methods to Solidago are usually time-consuming and using high amounts of undesirable in food and health products hazardous organic solvents, which should be removed from the final extracts to the maximum levels established by regulations. In addition, traditional extraction techniques may cause thermal/oxidative degradation of sensitive constituents (e.g. during reflux boiling) and cause environmental pollution. Therefore, green separation processes such as supercritical fluid extraction with carbon dioxide (SFE-CO₂) have been extensively studied as an alternative for the isolation and fractionation of compounds from natural sources (Reverchon & De Marco, 2006). SFE-CO₂ provides solvent-free extracts; however, it may extract only lipophilic nonpolar compounds, whereas many polar polyphenolic phytochemicals are insoluble or poorly soluble in CO₂. Their recovery from botanicals requires higher polarity solvents, which should be applied in conventional or more modern pressurized liquid (PLE), ultrasound assisted and/or microwave extraction methods. To the best of our knowledge the application of SFE-CO₂ and PLE has not been reported for the isolation and fractionation of goldenrod leaf constituents previously.

The main goals of this study were to evaluate various schemes for fractionating goldenrod leaves using high pressure extraction methods (SFE-CO₂ and PLE) and to evaluate antioxidant properties of the fractions obtained and recovery of phytochemicals. Antioxidant potential of fractions was assessed using several in vitro (ABTS, ORAC and TPC) and in situ assays. The extracts were prepared using different polarity solvents, while the insoluble plant material and extraction residues were assessed by the direct measurement of antioxidant activity indicators by applying to the plant solid substances the so-called QUENCHER method. Phytochemical composition was screened by ultra performance liquid chromatography with hybrid electron spray ionisation quadruple and time-of-flight mass spectrometry (UPLC/ESI-QTOF-MS). Such systematic approach is expected to provide more comprehensive data on antioxidant properties and the possibilities of obtaining phytochemical fractions from goldenrod. The data may be used for the up-scaling the production of functional ingredients from goldenrod to industrial levels and for preliminary prognosis of their uses and possible health benefits.