243
ORAC Oxygen radical absorbance capacity
HBA
Hydrogen bond acceptor
HBD
Hydrogen bond donor
HRE
High reflux extraction
MAE
Microwave-assisted extraction
RSM
Response surface methodology
SPE
Solid phase extraction
UAE
Ultrasound-assisted extraction
7.1 Introduction and Positioning of the Review
Ionic liquids have been used for more than 20 years as media for the extraction of
natural products from various matrices (Tang et al. 2012; Ventura et al. 2017). Some
comparative studies have shown that they have the potential to outperform conventional solvent extraction at the industrial level, for example, for artemisinin extraction (Lapkin et al. 2006). However, industrial development of ionic liquids as
extractants for natural products is facing strong issues including their cost, sourcing,
and “green” nature that remains somewhat questionable (Plechkova and Seddon
2008; Romero et al. 2008). As early as the mid-2000s, new ionic liquids started
being developed to meet those requirements (Pena-Pereira and Namieśnik 2014)
while keeping their modular character (Abbott et al. 2001; Dai et al. 2013a). In this
context, biosourced ionic liquids appeared, for example, based on natural amino
acids (Fukumoto et al. 2005; Gao et al. 2005). With the aim of employing always
greener solvents along with cheaper processes, a new class of tunable solvents has
emerged over the last 10 years, the deep eutectic solvents (DES) (Abbott et al.
2004), also called low-transition temperature mixture (LTTM). A further step has
been taken, thanks to the development of the even more eco-friendly natural deep
eutectic solvents (NADES), only prepared from natural products (Vanda et al.
2018). To date (2000–2019), more than 2000 publications deal with the extraction
of natural products in deep eutectic solvent.
Considering the extraction of polyphenols themselves, a hundred of publications
focusing on the use of deep eutectic solvent and natural deep eutectic solvent can be
found between 2012 and 2019, showing the growing interest of these solvents in the
field (Huang et al. 2019b). Almost all types of plant and different extraction processes have been evaluated (Zainal-Abidin et al. 2017; Cvjetko Bubalo et al. 2018;
Cunha and Fernandes 2018). Because polyphenols are widely present in the vegetable kingdom, in its broad sense, i.e., not only plants but also algae, they are frequently considered in extraction studies beyond their economic potential in many
industrial fields such as cosmetics, pharmaceuticals, and agrifood. The rich variety
of polyphenols and their sources allow variation of both targets and matrices
(Ruesgas-Ramón et al. 2017). While all polyphenol families have been studied, flavonols and flavones are by far the most investigated (see Sect. 7.2). They represent
the largest part of publications dealing with the extraction of polyphenols by eutectic solvents, whatever the associated extraction technology (Fig. 7.1).
7 Extraction of Plant and Algal Polyphenols Using Eutectic Solvents
ORAC Oxygen radical absorbance capacity
HBA
Hydrogen bond acceptor
HBD
Hydrogen bond donor
HRE
High reflux extraction
MAE
Microwave-assisted extraction
RSM
Response surface methodology
SPE
Solid phase extraction
UAE
Ultrasound-assisted extraction
7.1 Introduction and Positioning of the Review
Ionic liquids have been used for more than 20 years as media for the extraction of
natural products from various matrices (Tang et al. 2012; Ventura et al. 2017). Some
comparative studies have shown that they have the potential to outperform conventional solvent extraction at the industrial level, for example, for artemisinin extraction (Lapkin et al. 2006). However, industrial development of ionic liquids as
extractants for natural products is facing strong issues including their cost, sourcing,
and “green” nature that remains somewhat questionable (Plechkova and Seddon
2008; Romero et al. 2008). As early as the mid-2000s, new ionic liquids started
being developed to meet those requirements (Pena-Pereira and Namieśnik 2014)
while keeping their modular character (Abbott et al. 2001; Dai et al. 2013a). In this
context, biosourced ionic liquids appeared, for example, based on natural amino
acids (Fukumoto et al. 2005; Gao et al. 2005). With the aim of employing always
greener solvents along with cheaper processes, a new class of tunable solvents has
emerged over the last 10 years, the deep eutectic solvents (DES) (Abbott et al.
2004), also called low-transition temperature mixture (LTTM). A further step has
been taken, thanks to the development of the even more eco-friendly natural deep
eutectic solvents (NADES), only prepared from natural products (Vanda et al.
2018). To date (2000–2019), more than 2000 publications deal with the extraction
of natural products in deep eutectic solvent.
Considering the extraction of polyphenols themselves, a hundred of publications
focusing on the use of deep eutectic solvent and natural deep eutectic solvent can be
found between 2012 and 2019, showing the growing interest of these solvents in the
field (Huang et al. 2019b). Almost all types of plant and different extraction processes have been evaluated (Zainal-Abidin et al. 2017; Cvjetko Bubalo et al. 2018;
Cunha and Fernandes 2018). Because polyphenols are widely present in the vegetable kingdom, in its broad sense, i.e., not only plants but also algae, they are frequently considered in extraction studies beyond their economic potential in many
industrial fields such as cosmetics, pharmaceuticals, and agrifood. The rich variety
of polyphenols and their sources allow variation of both targets and matrices
(Ruesgas-Ramón et al. 2017). While all polyphenol families have been studied, flavonols and flavones are by far the most investigated (see Sect. 7.2). They represent
the largest part of publications dealing with the extraction of polyphenols by eutectic solvents, whatever the associated extraction technology (Fig. 7.1).
7 Extraction of Plant and Algal Polyphenols Using Eutectic Solvents