Exploitation of artichoke byproducts to obtain bioactive extracts enriched in inositols and caffeoylquinic acids by Microwave Assisted Extraction
Introduction
The globe artichoke (Cynara scolymus L.) is a perennial herbaceous crop, originated from the Mediterranean countries which contribute significantly to the local agricultural economy. Its highest total world production is concentrated in Italy (about 377,000 t annually) followed by Spain (224,000 t) and Egypt (180,000 t) [1].
Artichoke also has an important role in human health and nutrition as it is a natural source rich in phenolic compounds (mainly caffeoylquinic acids), inulin, cyclitols, sterols and sesquiterpenes [2]. Antioxidant activity of artichoke extracts is mainly attributed to caffeic acid and caffeoylquinic acids with chlorogenic acid (5-O-caffeoylquinic acid) as the most important of these derivatives [3]. Moreover, other health benefits have been reported for these phenolic compounds such as lipid-lowering, diuretic anti-inflammatory, anti-carcinogenic effects, etc. [4]. Other constituents, such as myo- and chiro-inositol, which belong to cyclitols family, possess insulin-mimetic properties, improving insulin resistance [5] and have shown antihiperglycemic [6] and hepatoprotective [7] activities, among others.
However, it is worth noting that only artichoke inner bracts and heart (called capitulum or head) are considered edible parts, which constitute only 15–20% of total biomass of the plant. At the end of the crop cycle, aboveground biomass residues (leaves, stalks and heads) of this plant are generally thought useless and are either burned or buried [8]. Nevertheless, they can represent a potential added value product to be used for bioenergy [8] or for technological purposes [9].
Nowadays, there is a general trend towards the valorization of food and agro-industrial residues as a cheap and suitable source of functional compounds. The transformation of artichoke wastes in higher added value products reduces the cost and generates additional profits for the industry. Therefore, there is a great interest in developing sustainable processes for the revalorization of artichoke residues [10,11] as a potential source of health-promoting antioxidant polyphenols [3,12], essential oils [13] and bioactive carbohydrates [14]. At present, most studies have been focused on artichoke flowers [14,15], although leaves and stalks are the most important residues [2,16] which are mainly used in pharmaceutical preparations.
It is known that the concentration and type of compounds detected in artichoke depends on the plant part, on its origin and growth conditions and, also, on the extraction process. Suitable extraction methods must be developed to exploit artichoke byproducts and isolate their bioactive components for their use as dietary supplements or food additives [14]. In the last years, several non-conventional extraction techniques have been developed such as pressurized liquid extraction (PLE), microwave assisted extraction (MAE) and supercritical fluid extraction (SFE). As compared to conventional solid-liquid extraction (SLE), these techniques are generally faster and more efficient to obtain plants extracts enriched on bioactives [17]. PLE and MAE have recently been applied to the extraction of inositols and inulin from artichoke bracts [14]. MAE was found to be more effective for the extraction of these bioactive cyclitols, whereas PLE provided higher yields of inulin. Recently, Pagano et al. [11] used pressurized hot water extraction (PHWE) to recover caffeoylquinic acids and flavone glycosides from agro-industrial artichoke by-products. However, to the best of our knowledge, no studies have been carried out for the simultaneous extraction of bioactive carbohydrates and phenolic compounds by none of these advanced extracting techniques.
High resolution analytical techniques such as gas chromatography (GC) and liquid chromatography (LC) have been widely used for the analysis of bioactive compounds in different food matrices, including artichoke residues [14,18]. Gas chromatography coupled to mass spectrometry (GC-MS) benefits from its high resolving power, sensitivity, selectivity and specific fragmentation information, useful for structural characterization [19]. However, for the analysis of polar compounds a derivatization step is necessary, which sometimes is not easy and has to be optimized [20]. Whereas silylation is a well-established procedure for derivatization of carbohydrates [20], it is not so straightforward for caffeoylquinic acids. Moreover, different reagents and conditions should be optimized to avoid partial derivatization reactions. Although GC–MS has been extensively used for the analysis of carbohydrates [14], only few works can be found dealing with its application for the analysis of caffeoylquinic acids in different natural matrices [21,22]. Nevertheless, to the best of our knowledge, no studies have been carried out for the simultaneous analysis of caffeoylquinic acids and carbohydrates by GC–MS of artichoke residues.
In this work, a new methodology based in MAE followed by GC-MS for the simultaneous extraction and analysis of low molecular weight carbohydrates and caffeoylquinic acids from artichoke byproducts (external bracts, leaves, stalks and receptacles) has been developed. The antioxidant activity of the extracts was also considered for the optimization of the method.
Section snippets
Reagents and samples
Analytical standards of glucose, fructose, sucrose, myo-inositol, scyllo-inositol, chiro-inositol, quinic acid, caffeic acid, chlorogenic acid and phenyl-β-glucoside (internal standard) were obtained from Sigma Aldrich (Madrid, Spain). Derivatization reagents including hydroxylamine chloride, anhydrous piridine, hexamethyldisilazane (HMDS), trifluoroacetic acid (TFA), trimethylsilyl imidazole (TMSI) and N,O-bis(trimethylsilil)trifluoroacetamide (BSTFA) with 1% trimethylchlorosilane (TMCS) were
Optimization of caffeoylquinic acids derivatization
Considering the high sensitivity, resolution power and identification capacity of GC-MS, this technique was selected for the analysis of inositols and caffeoylquinic acids in artichoke extracts. Derivatization procedure must be carefully optimized to confer stability and reproducibility of analysis of derivatives and to avoid partial derivatizations [25]. Taking into account the difficulties described above for the derivatization of some polar compounds, in this work, an optimization and
Conclusions
The new methodology developed by MAE has been found to be a fast and green technique for the extraction of bioactive compounds from artichoke byproducts with potential interest for the food industry. The study and optimization of experimental parameters affecting the extraction efficiency and selectivity of MAE, provided the optimal conditions to recover bioactive inositols, caffeoylquinic acids and total phenolic compounds from artichoke wastes (stalks, leaves, receptacles and external
CRediT authorship contribution statement
A. Mena-García: Data curation, Investigation, Methodology, Validation, Writing - original draft. S. Rodríguez-Sánchez: Investigation, Methodology, Validation. A.I. Ruiz-Matute: Conceptualization, Investigation, Methodology, Writing - original draft, Writing - review & editing. M.L. Sanz: Conceptualization, Funding acquisition, Investigation, Methodology, Supervision, Writing - original draft, Writing - review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work has been funded by Ministerio de Economía, Industria y Competitividad (MINECO) of Spain (project AGL2016-80475-R) and by the Comunidad of Madrid and European funding from FSE and FEDER programs (project S2018/BAA-4393, AVANSECAL-II-CM).
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2022, Food Research InternationalCitation Excerpt :Furthermore, other phenolic compounds, such as apigenin and luteolin glycosides have also been identified in artichoke leaves and bracts (Pagano et al., 2018). Artichoke receptacles extract presented higher total phenolic content (TPC: 46.99 mg GAE/g) and antioxidant capacity (DPPH: 122.99 mg TE/g), and were the richest in caffeoylquinic acids, while leaves extract showed the highest concentration of inositols (Mena-García et al., 2019). Notwithstanding, it has been reported in other studies that artichoke stem extracts present higher total phenolic (TPC: 45.7 mg GAE/g), vitamin C (2.0 mg/g) and chlorogenic acid (21.4 mg/g) contents than artichoke bracts, having higher extraction yields in high temperatures and with ultrasound or pressurized hot water applications (Borsini et al., 2021; Pagano et al., 2018; Reche et al., 2021).