a polyatomic inorganic anion, are becoming popular and high extraction yields are
expected due to their chemical nature. They are considered as green solvents
(Eppink et al. 2017; Halim et al. 2012a; Kumar et al. 2016), because they reduce
energy consumption, allow the use of alternative solvents and renewable natural
products, and ensure a safe and high-quality extract/product” (Chemat et al. 2012).
Ionic liquids are nonvolatile, thermally stable, and also have the capacity to
disturb cells and destabilize them (Park et al. 2015). Grosso et al. (2015) suggest the
use of switchable solvents to improve the extraction, using an alcohol and an amine
base in a nonionic state that after injection of CO 2 turn into an ionic liquid; finally,
to recycle the solvent, N 2 is injected through the solvent turning it back to nonionic
state. There is another kind of switchable solvents, such as hydrophilic solvents
(Boyd et al. 2012; Jessop et al. 2012). Some interesting reviews about green
extraction were made by Du et al. (2015) and Jeevan Kumar et al. (2017). Green
techniques allow a lower use of solvent, improve product quality, do not affect other
biocompounds, and, moreover, induce a decrease in energy consumption (Jeevan
Kumar et al. 2017). Emerging green solvents include natural or deep eutectic
solvents (NADESs) and supramolecular solvents (SUPRASs). NADESs play a role
as alternative media to water in living organisms. The main reason to use this other
medium is to help survival of any organism under harsh conditions, such as cold or
dryness, and therefore, NADESs are mostly made up of sugars, urea, choline
chloride, and organic acids (Jeevan Kumar et al. 2017). SUPRASs are nanostructured liquids that consist of assemblies of amphiphiles dispersed in a continuous
phase.
Novel approaches consist in combining a disruption method with an extraction
method to enhance the global process and make it greener as is the case with
microwave-assisted extraction (MAE) or ultrasound-assisted extraction (UAE),
enzyme-assisted extraction (EAE), pressurized liquid extraction (PLE) combined
with solvent extraction or other techniques (Ibañez et al. 2012; Kadam et al. 2013).
Regarding protein extraction, fragile proteins are of economic interest and
extraction of the protein fraction after cell lysis using mild technologies is incipient
(Eppink et al. 2017). Proteins are mainly recovered with solvents by filtration
(micro- and ultrafiltration) (Marrone et al. 2017) or through precipitation by pH
shifting (Ursu et al. 2014). Extraction of proteins through tangential ultrafiltration
and neutral pH has a relatively high yield without alteration of protein functionality
(Ursu et al. 2014). Filtration requires little energy and is considered a green and
mild process because it does not change protein state compared to extraction with
solvents (Safi et al. 2017). However, precipitation is considered a better option to
obtain protein powder and also to reduce the operating costs (Ursu et al. 2014).
A recent interest has emerged for the use of polymers within the aqueous two-phase
system (ATPS) looking for mild separation and extraction of proteins. This system
is prepared using a polymer–polymer and a polymer–salt mixture in such a way that
two water-rich phases are formed, thus providing the necessary gentle solvent for
proteins that does not affect their functionality. Zhao et al. (2014) proposed a
multiple stage ATPS extraction in order to increase purity of C-phycocyanin from
Spirulina platensis. Phong et al. (2017a) combined UAE and ATPS for protein
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P.-L. Gorry et al.
expected due to their chemical nature. They are considered as green solvents
(Eppink et al. 2017; Halim et al. 2012a; Kumar et al. 2016), because they reduce
energy consumption, allow the use of alternative solvents and renewable natural
products, and ensure a safe and high-quality extract/product” (Chemat et al. 2012).
Ionic liquids are nonvolatile, thermally stable, and also have the capacity to
disturb cells and destabilize them (Park et al. 2015). Grosso et al. (2015) suggest the
use of switchable solvents to improve the extraction, using an alcohol and an amine
base in a nonionic state that after injection of CO 2 turn into an ionic liquid; finally,
to recycle the solvent, N 2 is injected through the solvent turning it back to nonionic
state. There is another kind of switchable solvents, such as hydrophilic solvents
(Boyd et al. 2012; Jessop et al. 2012). Some interesting reviews about green
extraction were made by Du et al. (2015) and Jeevan Kumar et al. (2017). Green
techniques allow a lower use of solvent, improve product quality, do not affect other
biocompounds, and, moreover, induce a decrease in energy consumption (Jeevan
Kumar et al. 2017). Emerging green solvents include natural or deep eutectic
solvents (NADESs) and supramolecular solvents (SUPRASs). NADESs play a role
as alternative media to water in living organisms. The main reason to use this other
medium is to help survival of any organism under harsh conditions, such as cold or
dryness, and therefore, NADESs are mostly made up of sugars, urea, choline
chloride, and organic acids (Jeevan Kumar et al. 2017). SUPRASs are nanostructured liquids that consist of assemblies of amphiphiles dispersed in a continuous
phase.
Novel approaches consist in combining a disruption method with an extraction
method to enhance the global process and make it greener as is the case with
microwave-assisted extraction (MAE) or ultrasound-assisted extraction (UAE),
enzyme-assisted extraction (EAE), pressurized liquid extraction (PLE) combined
with solvent extraction or other techniques (Ibañez et al. 2012; Kadam et al. 2013).
Regarding protein extraction, fragile proteins are of economic interest and
extraction of the protein fraction after cell lysis using mild technologies is incipient
(Eppink et al. 2017). Proteins are mainly recovered with solvents by filtration
(micro- and ultrafiltration) (Marrone et al. 2017) or through precipitation by pH
shifting (Ursu et al. 2014). Extraction of proteins through tangential ultrafiltration
and neutral pH has a relatively high yield without alteration of protein functionality
(Ursu et al. 2014). Filtration requires little energy and is considered a green and
mild process because it does not change protein state compared to extraction with
solvents (Safi et al. 2017). However, precipitation is considered a better option to
obtain protein powder and also to reduce the operating costs (Ursu et al. 2014).
A recent interest has emerged for the use of polymers within the aqueous two-phase
system (ATPS) looking for mild separation and extraction of proteins. This system
is prepared using a polymer–polymer and a polymer–salt mixture in such a way that
two water-rich phases are formed, thus providing the necessary gentle solvent for
proteins that does not affect their functionality. Zhao et al. (2014) proposed a
multiple stage ATPS extraction in order to increase purity of C-phycocyanin from
Spirulina platensis. Phong et al. (2017a) combined UAE and ATPS for protein
106
P.-L. Gorry et al.