Extraction of phenolic compounds and anthocyanins from juçara (Euterpe edulis Mart.) residues using pressurized liquids and supercritical fluids
Graphical abstract
Introduction
Many researchers have been looking for new sources of natural bioactive compounds in order to make human diet healthier and more functional. Juçara (Euterpe edulis Mart.) is a tropical palm tree belonging to the Arecaceae family and widely spread in the Brazilian Atlantic forest. The juçara palm produces a spherical fruit rich in phenolic compounds, especially anthocyanins [1], [2], [3], which are found in higher amounts than in grumixama, jabuticaba [4], grapes and other fruits [5]. Anthocyanins are a class of phenolic compounds that are attracting a lot of interest because of the scientific evidence suggesting potentially beneficial health effects associated with its consumption [6], [7], [8]. These effects are thought to be related with their high antioxidant capacity and inhibition of DNA damage in cells [9], [10], [11].
In the industrial processing of juçara, the pericarp is macerated and separated from the epicarp (peel) and seeds by a sieving process, so peel and seeds become residues. Anthocyanins are concentrated in the cell vacuoles of peels, which are removed during processing, being therefore a rich raw material that can be used for the extraction of these compounds [12].
Large amounts of by-products and residues generated in fruit processing industries, such as juçara, are traditionally treated as environmental contaminants that need adequate disposal. These residues have been recognized as low cost sources for the obtaining of compounds with biological properties and high added value [13], [14], [15].
Anthocyanins have been traditionally extracted through low pressure methods, such as soaking, stirring, Soxhlet and Ultrasound-assisted Extraction [16], [17], [18], [19], [20], [21]. Nevertheless, there is an increasing demand for extraction processes with reduced solvent consumption, high yields and lower environmental impact. Additionally, solvent-free extracts or extracts obtained with GRAS solvents are required in order to sustain their use by the food, pharmaceutical and cosmetic industries.
Pressurized Liquid Extraction (PLE) is emerging as an alternative to conventional extraction methods that consume of large amounts of solvents and require long extraction times. It is known as an efficient technology for the extraction of nutraceutical compounds from different vegetables and food sources. PLE involves the use of liquid solvents at elevated temperatures, using pressures that can range from 4 to 20 MPa, which allow keeping the solvent in the liquid state even when operating at temperatures above their boiling point [22], [23], [24]. Pressure may affect the diffusion of the solvent into the pores of the raw material matrix, enhancing the contact of the target compound with the solvent [24], [25], [26]. PLE processes are generally performed at high temperatures, which increase the mass transfer rate of the compounds from the raw material to the solvent [27]. The increase of temperature enhances the solubility of target compounds and their diffusivity, and disrupts solute-matrix bonds, besides reducing viscosity and surface tension of the solvent [24], [28].
PLE has been successfully applied to recover anthocyanins from blackberry, blueberry, jabuticaba residues and others [29], [30], [31], [32], [33], [34]. However, due to the high process temperatures, degradation of anthocyanins may take place during the extraction. On the other hand, since PLE is performed in a closed system, the occurrence of oxidation reactions is limited by the lack of oxygen.
Supercritical Fluid Extraction (SFE) also presents considerable advantages over the conventional methods. Supercritical carbon dioxide (CO2) is recognized as an ideal solvent to selectively extract soluble compounds from vegetable raw materials [24]. It is a nontoxic, non-explosive and readily available solvent, easy to remove from the final extract, and does not lead to large chemical changes in biocompounds, preserving their biological properties [35], [36], [37]. However, supercritical CO2 is a non-polar solvent which has affinity to non-polar or low polar compounds, so its use for the extraction of polar compounds as anthocyanins has limitations. In this case, the addition of a cosolvent to change the non-polar nature of supercritical CO2 is required to improve its affinity towards anthocyanins [38], [39], [40].
In this context, the aim of this work was to obtain phenolic compounds and anthocyanins from juçara (Euterpe edulis Mart.) residues using high pressure extraction techniques (PLE and SFE). Ultrasound-assisted Extraction (UAE), Soxhlet extraction and Agitated Bed Extraction (ABE) were also carried out for comparison with the high pressure extraction methods.
Section snippets
Raw material
The residue from juçara processing, composed by peels and pulp located near the seeds, was provided by the company “Sitio do Bello” (Paraibuna, SP, southeastern Brazil). The samples used for the SFE experiments were previously freeze-dried, and the fresh samples were used in PLE.
After freeze-drying the residue presented the following characteristics: moisture determined by the method 934.06 [41]: 73.3 ± 0.6% dry basis (d.b.); lipids determined by the method 963.15 [41]: 2.3 ± 0.3% d.b.; proteins
Pressurized liquid extraction (PLE)
Table 1 presents the total phenolic content (TPC), monomeric anthocyanins content (MAC), the antioxidant activities evaluated by DPPH and ORAC assays and the concentrations of anthocyanins found by UPLC in the PLE extracts obtained from juçara residue.
Conclusions
PLE and SFE proved to be effective techniques to obtain phenolic compounds and anthocyanins with high antioxidant activity from juçara residues, encouraging their use in different applications. PLE with acidified solvents at mild temperatures (40 °C) allows obtaining extracts rich in anthocyanins, and SFE proved to be the most selective process for anthocyanin extraction. The use of an acidified ethanol + water mixture as cosolvent increased the polarity of supercritical CO2 and thus allowed the
Acknowledgements
The authors wish to thank CNPq (130739/2014-6 and 300533/2013-6) for support in form of a scholarship, CAPES (2952/2011) and FAPESP for financing this research (Projects 2013/04304-4, 2013/02203-6 and 2015/11932-7). The authors also acknowledge the support from the Laboratory of Bioactive Compounds (FEA-UNICAMP) for the analyses of the samples.
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