Page 309 - Advances in Eco-Fuels for a Sustainable Environment

266 Advances in Eco-Fuels for a Sustainable Environment

Carotenoids such as β-carotene, astaxanthin, and canthaxanthin are abundant in
Dunaliella, Haematococcus, and Chlorella [116, 119]. Organic solvent extraction
and supercritical fluid extraction are commonly employed to separate carotenoids
from the microalgae cell [27]. Organic solvents utilized are diethyl formamide, meth-
anol, ethanol, and acetone with homogenization, grinding, or sonication as pre-
treatment to disrupt the cell wall [120]. Pulsed electric field (PEF) is one of the
pretreatment used to break cell wall of microalgae. PEF assisting in solvent extraction
to improve the extraction efficiency of lipid and other valuable intracellular compo-
nents from microalgae. PEF can increase carotenoid yield up to 68.75% from extrac-
tion [121]. Mixture of dimethyl sulfoxide and water as the solvent can extract
carotenoids around 10mg/g without pre-treatment which is higher than using ethanol
as the solvent [114]. Ultrasound can be used to disrupt the microalgae cell wall to
release lipids and carotenoids.
Jaeschke et al. [121] stated that carotenoid extraction is affected by the concentra-
tion of solvent and ultrasound intensity. Best results were obtained under 50% ultra-
sound intensity and 75% ethanol concentration, which resulted in 1.31 0.04mg/g
carotenoids. However, the high power of ultrasound and the longer time of extraction
may cause degradation of the compound [121]. To eliminate harmful environmental
effects, a green solvent can be an alternative to extract carotenoids. Damergi et al.
[122] extracted carotenoids from C. vulgaris using 2-methyltetrahydrofuran
(MTHF) combined with ethanol. At 110°C and 30min extraction, the carotenoids
obtained were 277 3.8μg/g DW from wet microalgae (50% moisture). Other
research conducted by Singh et al. [119] reported that ultrasonication followed by
maceration gave the highest extracted carotenoid amount, which was 16.39mg/g com-
prising 69% zeaxanthin and 31% β-carotene.
The main obstacle in using organic solvents is the environmental concern. Most
organic solvents are toxic and harmful to the environment. Supercritical fluid extrac-
tion (SFE) can be an alternative extraction process. The common fluid used is carbon
dioxide due to it being cheap, easily available, inert, and nonflammable [120]. Other
solvents used in SFE to extract lipid soluble natural compounds are ethane, propane,
n-butane, and dimethyl ether (DME) [123]. Extraction of lipids and carotenoids under
supercritical carbon dioxide was reported by Liau et al. [124] by adding cosolvent
(ethanol 16.7% wt.) at 350bar and 323K; 7.61mg carotenoids/g and 239.7mg
triglyceride/g were extracted. Marcias-sanchez et al. [125] extracted carotenoids
under SFE condition (60°C, 300bar) and yielded 14.92 0.89μg carotenoids/mg
dry microalgae. Goto et al. [126] used subcritical dimethyl ether (DME) to extract
carotenoids from U. pinnatifida and obtained 390μg fucoxanthin/g biomass. Feller
et al. [123] applied subcritical n-butane to extract lipids and other components such
as polyunsaturated fatty acids and carotenoids from P. cruentum, and yielded
5.2 0.7mg carotenoids/g extract weight. SFE is more selective in extracting target
compounds but is not suitable for extracting polar compounds because of low polarity
of the solvent; cosolvent addition can be applied because carotenoids are more polar
than triglycerides (TG) [117, 123].
Purification of extracted carotenoids usually uses a saponification-solvent extrac-
tion based on the Willstatter method. Alkalines such as KOH or NaOH are usually