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P. R. Gogate and S. M. Joshi
13.3.6 Microwave Assisted Extraction (MAE)
Over the last decade there has been a focus on usage of irradiations like microwave
in processes of pigment or antioxidant extraction from plant sources. Microwaves
are electromagnetic radiations with a frequency in range of 300 MHz to 300 GHz
and transfer heat to the medium by ionic conduction and dipole rotation. Microwaves
when used as irradiating source in microalgae treatment process result in rapid heating
and also pressure changes across intracellular components and outer system resulting
in cell wall and membrane rupture which further helps in efficient solvent diffusion
giving higher pigment extraction (Leonelli et al. 2012). MAE is reported to demonstrate higher yields of pigments with lesser requirement of solvents and processing
time making the process more energy efficient (Pasquet et al. 2011). In the case
of lipid extraction from marine algae, MAE was reported to be the most efficient
technique as compared to processes like bead-beating, autoclaving or maceration
(Lee et al. 2010). MAE is generally performed in closed or open systems with the
open systems used for lower temperature requirement at atmospheric pressure while
closed systems are used in processes with higher temperatures and pressures.
Efficiency of MAE generally depends upon the microalgae cell structure and
extraction conditions. In a study performed on fucoxanthin extraction from Cylindrotheca closterium, it was reported that MAE at 50 W power for a period of 3–5 min
resulted in 4.24 μg/mg yield of fucoxanthin which was comparable to conventional
process of cold and hot soaking extractions (4.68 and 5.23 μg/mg as the yields,
respectively) though the conventional process required much higher time of 60 min
(Pasquet et al. 2011). It was also reported that MAE reduced the process time significantly till an optimum condition and further increase in power or time had no effect on
the yield. Another study on phycocyanin extraction from Porphyridium purpureum
using MAE applied for 10 s at 100 °C demonstrated yield of 34.8 ± 6.4 μg/mg
which was found equivalent to that obtained using the conventional solvent extraction method, though after higher time required as 60–80 min (Juin et al. 2014).
Another study on fucoxanthin extraction from U. pinnatifida established that MAE is
an effective approach giving maximum recovery of 109.3 mg/100 g under conditions
of 300 W as the power, solvent (ethanol) to sample ratio of 15:1 mL/g, temperature of
60 °C and treatment time of 10 min (Xiao et al. 2012). Study on astaxanthin recovery
from H. pluvialis performed in closed system (Ruen-ngam et al. 2011) demonstrated
that MAE is effective yielding 74% recovery of astaxanthin in only 5 min of extraction time at 75 °C using acetone as the solvent. Comparison of different solvents like
acetone, methanol, ethanol and acetonitrile was also performed in the same study
and acetone was established to be the most effective in the case of MAE. It was
also reported that an increase in temperature above 75 °C resulted in degradation
of astaxanthin. Zhao et al. (2009) presented an optimisation study of MAE with
response surface methodology and reported that 5.94 μg/mg as the maximum astaxanthin yield could be obtained under optimised parameters of 141 W power, 83 s
as the time, 9.8 mL as solvent volume with four cycles of extraction. It was also
reported that using higher power resulted in decreased astaxanthin yield, which can
P. R. Gogate and S. M. Joshi
13.3.6 Microwave Assisted Extraction (MAE)
Over the last decade there has been a focus on usage of irradiations like microwave
in processes of pigment or antioxidant extraction from plant sources. Microwaves
are electromagnetic radiations with a frequency in range of 300 MHz to 300 GHz
and transfer heat to the medium by ionic conduction and dipole rotation. Microwaves
when used as irradiating source in microalgae treatment process result in rapid heating
and also pressure changes across intracellular components and outer system resulting
in cell wall and membrane rupture which further helps in efficient solvent diffusion
giving higher pigment extraction (Leonelli et al. 2012). MAE is reported to demonstrate higher yields of pigments with lesser requirement of solvents and processing
time making the process more energy efficient (Pasquet et al. 2011). In the case
of lipid extraction from marine algae, MAE was reported to be the most efficient
technique as compared to processes like bead-beating, autoclaving or maceration
(Lee et al. 2010). MAE is generally performed in closed or open systems with the
open systems used for lower temperature requirement at atmospheric pressure while
closed systems are used in processes with higher temperatures and pressures.
Efficiency of MAE generally depends upon the microalgae cell structure and
extraction conditions. In a study performed on fucoxanthin extraction from Cylindrotheca closterium, it was reported that MAE at 50 W power for a period of 3–5 min
resulted in 4.24 μg/mg yield of fucoxanthin which was comparable to conventional
process of cold and hot soaking extractions (4.68 and 5.23 μg/mg as the yields,
respectively) though the conventional process required much higher time of 60 min
(Pasquet et al. 2011). It was also reported that MAE reduced the process time significantly till an optimum condition and further increase in power or time had no effect on
the yield. Another study on phycocyanin extraction from Porphyridium purpureum
using MAE applied for 10 s at 100 °C demonstrated yield of 34.8 ± 6.4 μg/mg
which was found equivalent to that obtained using the conventional solvent extraction method, though after higher time required as 60–80 min (Juin et al. 2014).
Another study on fucoxanthin extraction from U. pinnatifida established that MAE is
an effective approach giving maximum recovery of 109.3 mg/100 g under conditions
of 300 W as the power, solvent (ethanol) to sample ratio of 15:1 mL/g, temperature of
60 °C and treatment time of 10 min (Xiao et al. 2012). Study on astaxanthin recovery
from H. pluvialis performed in closed system (Ruen-ngam et al. 2011) demonstrated
that MAE is effective yielding 74% recovery of astaxanthin in only 5 min of extraction time at 75 °C using acetone as the solvent. Comparison of different solvents like
acetone, methanol, ethanol and acetonitrile was also performed in the same study
and acetone was established to be the most effective in the case of MAE. It was
also reported that an increase in temperature above 75 °C resulted in degradation
of astaxanthin. Zhao et al. (2009) presented an optimisation study of MAE with
response surface methodology and reported that 5.94 μg/mg as the maximum astaxanthin yield could be obtained under optimised parameters of 141 W power, 83 s
as the time, 9.8 mL as solvent volume with four cycles of extraction. It was also
reported that using higher power resulted in decreased astaxanthin yield, which can