314
P. R. Gogate and S. M. Joshi
almeriensis reported an optimum temperature and pressure of 46 °C and 600 bar,
respectively to obtain highest yield of lutein (Macías-Sánchez et al. 2010). Few
examples of SFE process with the information on typical yields are also mentioned
in Table 13.1.
Polarity modifiers like ethanol, vegetable oil and acetone have also been used
in many studies to improve the efficiency of pigment extraction. Co-solvents cause
swelling of algal cells and help in increasing the dissolution of pigments in supercritical CO 2 (Nobre et al. 2006; Poojary et al. 2016). In one of the study performed
on comparison of efficacy of co-solvents like ethanol, acetone, methanol, propanol
and butanol for extraction of pigments, it was reported that ethanol is the most effective co-solvent (Yen et al. 2012). In another study performed by Krichnavaruk et al.
(2008) using vegetable oil as co-solvent, it was reported that using 10% olive oil
increased pigment recovery up to 51% at 70 °C and 400 bar pressure (Krichnavaruk
et al. 2008). An another study reported on application of SFE on sea weed established sunflower oil to be an effective co-solvent as compared to canola oil, ethanol,
soybean oil and water (Saravana et al. 2017).
The processing of microalgae with disruption techniques like sonication, ball
milling, homogenisation also help in extraction of pigments during SFE process.
Homogenised form of microalga Synechococcus sp was subjected to SFE by Nobre
et al. (2006) and it was reported that pigment extraction was found to increase from
58 to 91% after homogenisation as pretreatment (Nobre et al. 2006). Overall it can
be said that SFE applied under optimised conditions of pressure and temperature
enhances the process of pigment extraction with selectivity of desired components
and addition of co-solvent further increases process efficiency. The SFE process can
also be combined with cell disruption to give process intensification resulting in
efficient processing.
13.3.3 Subcritical Fluid Extraction (SCF)
Subcritical fluid extraction is process similar to that SFE but requires lesser temperature and pressure conditions to operate using liquefied fuels (some typical examples
include subcritical CO 2 , 1, 1, 1, 2-tetrafluoroethane and dimethyl ether) as extraction
solvents. Process conditions generally employed in SCF extraction are temperature
in range of 40 to 45 °C, pressure upto 35 MPa with use of co-solvent such as 5%
loading of ethanol (Du et al. 2015). Extraction at lower temperatures results in efficient extraction of thermally labile pigments. In one of the studies, lutein extraction
from C. pyrenoidosa was performed with subcritical CO 2 and ethanol as co-solvent
resulting in 124 mg/100 g of lutein extraction (Fan et al. 2015). Use of dimethyl
ether (DME) as an extraction solvent was reported to offer advantage in that raw
sample of microalgae can be used directly without drying. DME can also be evaporated at lower pressures from extraction solution making the process more efficient
with lesser processing and time requirements (Kanda and Li 2011). Using DME as
solvent in SCF at 25 °C and 5.9 bar pressure for 0.72 h was reported to give yield of
P. R. Gogate and S. M. Joshi
almeriensis reported an optimum temperature and pressure of 46 °C and 600 bar,
respectively to obtain highest yield of lutein (Macías-Sánchez et al. 2010). Few
examples of SFE process with the information on typical yields are also mentioned
in Table 13.1.
Polarity modifiers like ethanol, vegetable oil and acetone have also been used
in many studies to improve the efficiency of pigment extraction. Co-solvents cause
swelling of algal cells and help in increasing the dissolution of pigments in supercritical CO 2 (Nobre et al. 2006; Poojary et al. 2016). In one of the study performed
on comparison of efficacy of co-solvents like ethanol, acetone, methanol, propanol
and butanol for extraction of pigments, it was reported that ethanol is the most effective co-solvent (Yen et al. 2012). In another study performed by Krichnavaruk et al.
(2008) using vegetable oil as co-solvent, it was reported that using 10% olive oil
increased pigment recovery up to 51% at 70 °C and 400 bar pressure (Krichnavaruk
et al. 2008). An another study reported on application of SFE on sea weed established sunflower oil to be an effective co-solvent as compared to canola oil, ethanol,
soybean oil and water (Saravana et al. 2017).
The processing of microalgae with disruption techniques like sonication, ball
milling, homogenisation also help in extraction of pigments during SFE process.
Homogenised form of microalga Synechococcus sp was subjected to SFE by Nobre
et al. (2006) and it was reported that pigment extraction was found to increase from
58 to 91% after homogenisation as pretreatment (Nobre et al. 2006). Overall it can
be said that SFE applied under optimised conditions of pressure and temperature
enhances the process of pigment extraction with selectivity of desired components
and addition of co-solvent further increases process efficiency. The SFE process can
also be combined with cell disruption to give process intensification resulting in
efficient processing.
13.3.3 Subcritical Fluid Extraction (SCF)
Subcritical fluid extraction is process similar to that SFE but requires lesser temperature and pressure conditions to operate using liquefied fuels (some typical examples
include subcritical CO 2 , 1, 1, 1, 2-tetrafluoroethane and dimethyl ether) as extraction
solvents. Process conditions generally employed in SCF extraction are temperature
in range of 40 to 45 °C, pressure upto 35 MPa with use of co-solvent such as 5%
loading of ethanol (Du et al. 2015). Extraction at lower temperatures results in efficient extraction of thermally labile pigments. In one of the studies, lutein extraction
from C. pyrenoidosa was performed with subcritical CO 2 and ethanol as co-solvent
resulting in 124 mg/100 g of lutein extraction (Fan et al. 2015). Use of dimethyl
ether (DME) as an extraction solvent was reported to offer advantage in that raw
sample of microalgae can be used directly without drying. DME can also be evaporated at lower pressures from extraction solution making the process more efficient
with lesser processing and time requirements (Kanda and Li 2011). Using DME as
solvent in SCF at 25 °C and 5.9 bar pressure for 0.72 h was reported to give yield of