Conventional extraction techniques: Solvent extraction

Abstract

Macroalgae represent a relatively untapped source of high-value compounds with unlimited possibilities and promising applications in the cosmetic, pharmaceutical, food, and animal feed industries. Conventional or solvent extraction protocols are still widely used by industry and researchers aiming to achieve high yields of compounds by operating relatively simple and affordable equipment. However, these extraction techniques are time-, energy-, and solvent-consuming procedures, raising both environmental and health and safety concerns. This chapter covers the principles, current equipment, and main process parameters aiming to obtain high-value compounds from macroalgae using steam distillation, maceration, and Soxhlet. The recent developments and novel technological designs aiming to overcome the limitations of these conventional methods are also discussed in detail together with the prospects and future technological trends in the field of conventional extraction.

Full text

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Conventional extraction
techniques: Solvent extraction
M Garcia-Vaqueroa, G Rajauriab, B Tiwaria
aDepartment of Food Biosciences, TEAGASC, Food Research Centre, Ashtown, Dublin 15, Ireland
bSchool of Agriculture and Food Science, University College Dublin, Lyons Research Farm, Celbridge, Co.
Kildare, Ireland
1INTRODUCTION
Macroalgae represent a relatively untapped source of high-value
compounds with unlimited possibilities and promising applications in
the cosmetic, pharmaceutical, food, and animal feed industries
(Garcia-Vaquero et al., 2019; Miranda et al., 2017). Macroalgae or
seaweed are able to adapt to the changes in the aquatic environment by
producing polysaccharides, proteins-peptides, phenols, and carotenoids
different in composition and biological properties to those found in
terrestrial plants (Garcia-Vaquero et al., 2019, 2017a; Ventura et al.,
2018). These high-value compounds could be incorporated into food
products to develop functional foods and nutraceuticals, providing health
benefits to consumers beyond basic nutrition (Garcia-Vaquero and Hayes,
2016). The market of functional foods and nutraceuticals has experienced
a fast growth during this last decade and it is estimated to be valued
in 94.21 billion USD by 2023 (Markets and Markets, n.d.). Moreover,
it is expected that the interest in extracting high-value compounds and
nutraceuticals will continue to grow as the consumer’s well-being and
health awareness are currently the main drivers of the agrifood market
(Hosni et al., 2017).
The main objective of any extraction technique is to maximize the
recovery of the target compounds from a sample matrix, while preserving
the integrity of the molecules of interest and decreasing the coextraction
of other impurities or undesirable compounds (Garcia-Vaquero et al.,
2018; Tiwari, 2015). Conventional or solvent extraction protocols are
still widely used by industry and researchers (Chemat and Boutekedjiret,
2016; Escorsim et al., 2018; Hernandez-Carmona et al., 2013). These
conventional protocols involve the extraction of compounds from a solid
matrix using solvents, namely, solid-
ISBN 978-0-12-817943-7, DOI: 10.1016/B978-0-12-817943-7.00006-8
Sustainable Seaweed Technologies © 2020.
1
CHAPTER 6

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2Sustainable seaweed technologies
liquid extraction techniques such as certain types of steam distillation,
maceration, and Soxhlet extraction (Tiwari, 2015; Wang and Weller,
2006). It has to be noted that these methods are generally very time
consuming and require large volumes of toxic organic solvents, raising
safety concerns for the workers exposed to these chemicals and the
consumers of the final food products or supplements (Tiwari, 2015).
These safety concerns, together with novel consumers’ driven preferences
toward more sustainable and natural food products, have benefited the
development of multiple novel technologies and processes with promising
industrial applications (Herrero and Ibañez, 2018; Tiwari, 2015;
Garcia-Vaquero et al., 2017b). However, conventional technologies are
still being used and improved aiming to adapt the traditional equipment to
the current needs of the market.
This chapter covers the principles, current equipment, and main
process parameters aiming to obtain high-value compounds from
macroalgae using steam distillation, maceration, and Soxhlet. The recent
developments and novel technological designs aiming to overcome the
main shortcomings of these conventional methods are also discussed in
detail together with the prospects and future technological trends in the
field of conventional extraction.
2DISTILLATION
2.1 Principles of distillation
Distillation techniques are mainly employed to separate binary and
multicomponent liquid mixtures by using the selective boiling points of
each component of the mixture followed by condensation steps (Górak
and Sorensen, 2014). This extraction and separation technique has been
used for over 5000 years (Kockmann, 2014) and the first books compiling
multiple distillation techniques and protocols to generate “distilled
waters” from plants and animals were published during the years 1481
and 1525 (Kockmann, 2014). Currently, this technique is still widely used
to purify or separate compounds in the chemical and petroleum refining
industries, representing up to 50% of the total energy consumption of
these industries per year (Górak and Sorensen, 2014).
When extracting natural products, distillation is the most traditional
method to isolate volatile molecules from other mixtures of compounds
or from multiple biological matrices, including macroalgae.

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Conventional extraction techniques: Solvent extraction 3
These extraction procedures can be divided into three main groups,
namely, water, water-steam, and steam distillation, being this later
technique the most widely applied to extract essential oils from plants
(Chemat and Boutekedjiret, 2016). Steam distillation is based on the
direct application of steam into a tank containing the samples, releasing
the essential oils from the matrix. The steam and essential oil vapors are
subsequently cooled and condensed to generate a mixture of oil and water
that can be easily separated (Chemat and Boutekedjiret, 2016).
Steam distillation is currently the most widely used technique in the
food industry when extracting volatile compounds. However, these
extraction methods are high-energy-consuming processes as the steam
distillation of volatiles requires long periods of time. Moreover, the
exposure of the volatile compounds to high temperatures during
prolonged periods of extraction could induce chemical modifications and
alter the properties of the extracted molecules (Chemat and Boutekedjiret,
2016).
Several modifications of the steam distillation equipment have been
designed aiming to improve the major drawbacks of this technology
and to adapt its use for multiple industrial purposes. The combination
of steam distillation with solvent extraction techniques resulted in the
development of steam distillation extraction or SDE apparatus, allowing
the simultaneous condensation of a steam distillate and an immiscible
extracting solvent (Likens and Nickerson, 1964). Further innovations
incorporated the use of microwave in multiple technological designs such
as microwave hydrodistillation, microwave accelerated steam distillation,
and microwave steam distillation among others (Chemat and
Boutekedjiret, 2016). Schemes of SDE and microwave steam distillation
technologies are represented in Fig. 1.
Novel steam distillation extractors have been explored for multiple
applications and are currently considered green extraction procedures.
The novel steam distillation procedures are highly efficient to recover
valuable compounds, while reducing the time, cycles of extraction, and
energy consumption when compared to the traditional steam distillation
apparatus (Bahramia et al., 2013; Kusuma and Mahfud, 2017; Sun et al.,
2017).

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4Sustainable seaweed technologies
Fig. 1 Schematic representation of (A) steam distillation extractor or SDE equipment
(modified from Likens, S., Nickerson, G., 1964. Detection of certain hop oil constituents
in brewing products. In: Proceedings. Annual Meeting—American Society of Brewing
Chemists. Taylor & Francis, pp. 5–13; Bahramia, G., Soltanib, R., Sajjadic, S.-E.,
Kananid, M.-R., Naderie, R., Ghiasvandf, N., Shokoohiniag, Y., 2013. Essential oil
composition of Ferula assa-foetida L. fruits from Western Iran. J. Rep. Pharm.Sci. 2,
90–97) and (B) a microwave steam distillation unit (modified from Chemat, F.,
Boutekedjiret, C., 2016. Extraction-steam distillation. Reference Module in Chemistry
Molecular Sciences and Chemical Engineering, pp. 1–11).
2.2 Applications of steam distillation
Steam distillation is the technique of choice to extract essential oils from
citrus peel according to the current ISO and AFNOR standards (Chemat
and Boutekedjiret, 2016). This technique has been recently used to extract
volatile compounds from jujube extracts, commonly used in the food
industry as an aromatic and flavoring agent (Sun et al., 2017). In the case
of macroalgae, Kajiwara et al. (1989) used steam distillation to extract and
characterize essential oils from Dictyopteris prolifera and Dictyopteris
undulata. Steam distillation was also employed by Karabay‐Yavasoglu et
al. (2007) to identify over 40 volatile compounds from macroalga Jania
rubens. Moreover, steam distillation techniques are the analytical tool of
choice to test certain quality parameters of biodiesel as recommended
by Chinese National standards (Chen et al., 2012). Thereby, steam
distillation at temperatures ranging from 266 to 368°C was used to test
the attributes of algal biodiesel obtained from microalgae Scenedesmus sp.
(Chen et al., 2012).

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Conventional extraction techniques: Solvent extraction 5
Steam distillation coupled with solvent extraction or SDE has been widely
used to characterize aromatic compounds from different varieties of tea
(Cao et al., 2018; Liang et al., 2005; Xu et al., 2016) and flavor
compounds from multiple food products such as potato snacks (Majcher
and Jeleń, 2009) and fermented soybean or “natto” (Liu et al., 2018).
SDE technique was successfully applied to extract brominated anisoles
and cresols from macroalgae Polysiphonia sphaerocarpa (Flodin and
Whitfield, 2000) and important flavor compounds such as bromophenols
from Padina arborescens,Sargassum siliquastrum, and Lobophora
variegata (Chung et al., 2003). Sun et al. (2012) used various SDE
methods to extract essential oils from Capsosiphon fulvescens. Based
on the analyses of the essential oils, the authors associated the presence
of large number of aldehydes and ketones with the characteristic flavor
of this green macroalgae. Similar distillation protocols were used by
Kajiwara et al. (1990) to conclude that aldehydes were the most prominent
volatile molecules in red macroalga Porphyra tenera. Moreover, SDE has
also been used in algae aiming to extract other nonvolatile high-value
compounds. Tanzi et al. (2013) employed SDE to generate lipid-rich
extracts from wet microalgae Nannochloropsis oculata and Dunaliella
salina. The authors did not appreciate differences in oil composition when
comparing SDE to other conventional extraction procedures; however,
the energy consumption was significantly lower using SDE compared to
Soxhlet (Tanzi et al., 2013).
SDE has also been used in the field of analytical chemistry to
determine the concentration of environmental pollutants (i.e., pesticides,
polychlorinated biphenyls, and polychlorinated dibenzo-p-dioxins and
furans). The recent scientific literature containing protocols and
applications of SDE to analyze multiple contaminants from inorganic
and biological samples have been reviewed in detail by Chemat and
Boutekedjiret (2016).
To the best of our knowledge, there are currently no reports available
on the use of microwave-assisted distillation processes in macroalgae.
However, these technologies have been successfully applied in a wide
variety of plants (Djouahri et al., 2013; Fadel et al., 2011; Kusuma and
Mahfud, 2017; Petrakis et al., 2014). All these previously cited studies
mentioned an increased efficiency of the novel distillation systems when
extracting volatile compounds compared to the traditional equipment.

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6Sustainable seaweed technologies
3MACERATION
3.1 Principles of maceration
Maceration is a widely used solid-extraction technique that achieves the
extraction of high-value compounds by selecting the polarity of the
solvent and applying heat and/or agitation to increase the solubility of
the compounds of interest from the sample (Luque de Castro and
Priego-Capote, 2010). The processes of maceration and filtration to obtain
macroalgal polysaccharides as described by Rioux et al. (2007) are
represented in several images in Fig. 2.
Fig. 2 Images showing (A) a maceration protocol using temperature and agitation to
extract polysaccharides from macroalgae; followed by (B) filtration of the mixture to
separate the extracted compounds from the algal biomass.

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Conventional extraction techniques: Solvent extraction 7
Maceration can be performed by using low-cost and easy-to-operate
equipment compared to other conventional and innovative extraction
techniques. Moreover, the maceration protocols can be adapted to extract
a wide variety of molecules by using multiple solvents, temperature,
and agitation combinations to facilitate a more selective and efficient
mass transfer of high-value compounds from the biomass. The major
drawbacks of maceration are the long times of extraction and large
volumes of solvent employed with these techniques (Sasidharan et al.,
2018; Gallo et al., 2017), together with the need to use several filtration
or centrifugation steps to separate the macroalgal biomass from the final
extracts (Cong et al., 2016, 2014; Rioux et al., 2007).
3.2 Applications of maceration
As previously mentioned, maceration protocols have been extensively
used to obtain natural compounds; however, these protocols are currently
being displaced by other solvent extraction techniques and innovative
technologies mainly due to their low efficiency and the long times of
extraction required (Luque de Castro and Priego-Capote, 2010). Despite
this decline, the use of maceration still endures in recent scientific studies
aiming to obtain natural products from macroalgae and screen the
biological activities of the extracts. Setha et al. (2013) researched the
antioxidant potential of Padina sp. by macerating the macroalgal biomass
in n-hexane, ethyl acetate, and methanol. Moreover, extracts from
macroalgae Gracilaria folifera and Sargassum longifolium generated by
maceration using petroleum ether, dichloromethane, chloroform, ethanol,
and water have also shown promising antioxidant and antibacterial
properties (Thanigaivel et al., 2015).
Several authors have also developed maceration protocols to obtain
high yields of valuable compounds from macroalgae. Thereby, Heffernan
et al. (2016) obtained higher yields of xanthophylls from Fucus serratus
by macerating the sample in a mixture of hexane and acetone at 50°C
for 24 h, compared to other innovative technologies such as supercritical
CO2extraction. Cong et al. (2016) used multiple maceration steps in
water at 100°C combined with filtration or centrifugation of the biomass
to obtain extracts rich in polysaccharides in the process of purification

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8Sustainable seaweed technologies
of fucoidans from brown macroalga Sargassum fusiforme (Cong et al.,
2016).
The use of multiple maceration steps changing the polarity of the
solvent and the temperature of extraction to target the extraction of certain
high-value compounds has also been explored. Thereby, the general
scheme to produce alginates from macroalgae is based on the maceration
of the biomass using an acidic solvent at room temperature followed by
the extraction of the macroalgal pellet with sodium carbonate solutions at
higher temperatures (Hernandez-Carmona et al., 2013). Cong et al. (2014)
macerated macroalgae Sargassum fusiforme in ethanol to obtain lipids
from the biomass before extracting the macroalgae in boiling water using
eight cycles of maceration of 4 h, aiming to increase the extraction yields
of alginates. Similarly, Rioux et al. (2007) used multiple maceration
steps with ethanol at various temperatures (23°C and 70°C) to obtain
pigments and proteins, followed by two cycles of 3 h of maceration in
an acidic solvent (HCl 0.01 M) at 70°C to obtain extracts containing
polysaccharides (alginates, fucoidan, and laminarin) from brown
macroalgae Ascophyllum nodosum,Fucus vesiculosus, and Saccharina
longicruris. Multiple protocols and combinations of solvents aiming to
achieve alginates, agar, and carrageenan from brown macroalgae using
maceration techniques have been reviewed in detail by
Hernandez-Carmona et al. (2013).
Maceration has also been used together with other conventional
techniques aiming to reduce the impurities or pretreat the biomass before
applying further extraction treatments to obtain the compounds of interest.
Véliz et al. (2018) obtained carrageenan from macroalgae
Chondracanthus chamissoi and Gelidium lingulatum by pretreating the
algal biomass using Soxhlet in methanol and acetone (1:1) to eliminate
pigments and lipids, followed by the extraction of carrageenans and agar
by macerating the macroalgae in water at 90–95°C for 3 h and continuous
stirring. Similarly, a Soxhlet pretreatment followed by maceration
extraction was also used by Matsuhiro et al. (2005) when extracting
sulfated galactans from red macroalgae Schizymenia binderi and by
Matsuhiro and Urzúa (1991) when extracting agar from Gelidium
chilense. Extraction protocols combining innovative technologies and
maceration techniques have also been used to increase the recovery yields
of high-value compounds from plants. Thereby, grape seeds treated with
sonication followed by maceration achieved extracts

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Conventional extraction techniques: Solvent extraction 9
with high yields of polyphenols and antioxidant activities (Da Porto et al.,
2013).
Novel developments in maceration techniques involve the use of
enzymes to treat the macroalgal biomass. These maceration
methodologies aim to degrade macroalgal polysaccharides that can act as
antinutritional factors in humans by limiting the activity of the digestive
enzymes (Fleurence, 2016). Polysaccharides from Undaria pinnatifida,
Laminaria japonica, and Hizikia fusiformis inhibited 21%, 55%, and
41% of pepsin activity in vitro, respectively (Horie et al., 1995). Thus,
the obtained macerated macroalgae could be considered as a novel food
product with improved nutritional value (Fleurence, 2016). Several
enzymatic treatments have been proposed to obtain macerated
macroalgae, although the efficiency of the method is extremely variable
depending on the polysaccharide composition of the different macroalgae
species (Fleurence, 2016; Fleurence et al., 2018). The use of enzymes
such as cellulases, xylanases, and β-glucanases improved the digestibility
of protein from Palmaria palmata and multiple maceration protocols have
been recently reviewed by Fleurence et al. (2018).
4SOXHLET EXTRACTION
4.1 Principles of Soxhlet extraction
Soxhlet extraction was developed in 1879 and since then, it is still
considered as the reference method to evaluate the performance of other
new solid-extraction procedures (Luque de Castro and Priego-Capote,
2010; Wang and Weller, 2006). In a traditional Soxhlet extractor, the
samples are placed in a thimble that will be loaded into a thimble-holder
and filled gradually with the fresh solvent of choice from a distillation
flask. Once the solvent reaches the overflow level, a siphon back aspirates
the liquid carrying the extracted compounds to the flask. The distillation
of the solvent contained in the flask ensures a continuous flow of fresh
solvent through the sample, repeating the operation until the full
extraction is achieved (Luque de Castro and Priego-Capote, 2010). A
scheme of a conventional Soxhlet extractor is shown in Fig. 3 (see Fig.
3A).
Soxhlet extraction offers certain advantages over other techniques
such as (1) the constant flow of fresh solvent to the sample, improving
the displacement of the transfer equilibrium that favors the extraction

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10 Sustainable seaweed technologies
Fig. 3 Soxhlet extraction devices: (A) Schematic representation of a traditional Soxhlet
extractor; and (B) picture of an automated Soxhlet extraction apparatus (E-812/E-816 HE,
Buchi AG, Switzerland).
of compounds; (2) a maintained heat effect on the sample; (3) the final
extract does not require filtration; and (4) several samples can be treated in
parallel using relatively low cost and easy operational processes compared
to other extraction techniques (Wang and Weller, 2006). However, this
technique has some disadvantages as the extraction requires long periods
of time using large amounts of solvents at boiling point that could degrade
the extracted high-value compounds. Moreover, this time-consuming
technique cannot be accelerated by using agitation and the organic
solvents used in the extraction will need to be removed from the final
product by evaporation, posing both economic and environmental risks
(Wang and Weller, 2006).
The traditional Soxhlet technique has been constantly improving since
its discovery, aiming to shorten the extraction times and automating the
process (Luque de Castro and Priego-Capote, 2010). Recent
developments include high-pressure Soxhlet extraction, supercritical
fluid-Soxhlet extractors, and automated Soxhlet extraction systems as the
one shown in the picture in Fig. 3 (see Fig. 3B).
The use of innovative technologies such as sonication has recently
expanded beyond their initial intended applications. Currently, significant
research efforts have been made aiming to increase the efficiency of
multiple traditional food processes or

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Conventional extraction techniques: Solvent extraction 11
conventional technologies by incorporating sonication. Thereby, the use
of ultrasounds has shown promising results improving food fermentation
processes (Ojha et al., 2015, 2017), salting-desalting steps (Inguglia et
al., 2017; Ojha et al., 2016), microbial inactivation or decontamination
of food (Condón-Abanto et al., 2018; Pedrós-Garrido et al., 2017),
development of drying technologies (Charoux et al., 2017), and food
enzymatic treatments (O’Donnell et al., 2010). Moreover, sonication
technologies have shown promising results when extracting high-value
compounds (i.e., polysaccharides and proteins) from multiple macroalgae
species (Garcia-Vaquero et al., 2017a, 2019, 2018) and microalgae
(Hayes et al., 2019, 2018; Ventura et al., 2018). Novel technological
designs have been developed aiming to improve the efficiency of
conventional Soxhlet extraction by using ultrasounds such as the
Ultrasound-assisted Soxhlet extractor proposed by Luque-Garcıa and De
Castro (2004) or the Sono-Soxhlet apparatus developed by Djenni et al.
(2013) represented schematically in Fig. 4.
Ultrasound-assisted Soxhlet uses an ultrasonic probe in the cartridge
compartment containing the sample (Luque-Garcıa and De Castro, 2004),
while in the Sono-Soxhlet apparatus the ultrasounds are
Fig. 4 Schemes on the application of ultrasounds aiding Soxhlet extraction: (A) image
of an ultrasound Soxhlet extractor proposed by Luque-Garcıa and De Castro (2004)
reproduced with permission from Elsevier; and (B) a schematic representation of a
Sono-Soxhlet apparatus developed by Djenni et al. (2013) and reproduced with permission
from Springer Nature.

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12 Sustainable seaweed technologies
applied directly in the thimble containing the sample (Djenni et al., 2013).
The application of ultrasounds in both technological designs resulted in
similar recovery yields and composition of the extracted compounds when
compared to the traditional Soxhlet, while improving the efficiency of the
process by decreasing significantly the time of extraction (Djenni et al.,
2013; Luque-Garcıa and De Castro, 2004).
Other technological improvements on the traditional Soxhlet apparatus
include the application of microwave technologies, developing multiple
technological designs such as the industrial equipment Soxwave-100
apparatus (Garcia-Ayuso et al., 1998; Luque de Castro and Priego-Capote,
2010).
4.2 Applications of Soxhlet extraction
The successful application of this technique will depend on the
characteristics of the matrix, i.e., the particle size of the sample could
limit the internal diffusion of the solvent during the extraction; and on
the selection of solvent to perform the Soxhlet extraction (Wang and
Weller, 2006). Hexane is considered the solvent of choice to extract
edible oils as it has excellent oil solubility and recovery of lipids (Wang
and Weller, 2006). Boni et al. (2018) recovered 24% of lipids from
microalgae Botryococcus braunii using 45 cycles of Soxhlet extraction
with n-hexane; while Satputaley et al. (2018) obtained 28% of algal oil
from dried Chlorella vulgaris using 8–10 Soxhlet cycles with n-hexane.
Other solvents such as isopropanol, ethanol, hydrocarbons, and mixtures
of multiple solvents have been also used in Soxhlet extractors to modify
the polarity of the liquid phase and increase the recovery of certain
molecules (Wang and Weller, 2006). Escorsim et al. (2018) obtained
higher yields of lipids from microalgae Acutodesmus obliquus using
ethanol: hexane mixtures compared to the use of both solvents separately
using a Soxhlet extraction apparatus for 12 h. These results could be
attributed to the effect of the intermediate polarities of the solvent
mixtures in improving the recovery of both polar and nonpolar lipids
simultaneously (Escorsim et al., 2018). In the case of macroalgae, a
Soxhlet apparatus was employed to extract oil from Cladophora
glomerata, obtaining the maximum recoveries from the biomass when
using a solvent mixture of methanol-chloroform at 65°C during 3.5 h
(Yuvarani et al., 2017). A similar solvent mixture (methanol: chloroform,
1:2) was used by Cheung et al. (1998) when extracting

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Conventional extraction techniques: Solvent extraction 13
lipophilic compounds from Sargassum hemiphyllum using a Soxhlet
apparatus aiming to analyze the fatty acid profile of this macroalgae.
The extraction and characterization of lipophilic compounds from
Himanthalia elongata,Laminaria ochroleuca,Cystoseira tamariscifolia,
and Sargassum muticum was performed by extracting the dried biomass
in a Soxhlet using dichloromethane for 9 h (Santos et al., 2016).
There is scarce literature on the use of Soxhlet extraction to obtain
high-value compounds other than lipids. Farzanah et al. (2019) used a
mixture of water and ethanol as a solvent during 10 h to determine the
total weight of extractives and the potential to produce biogas using
macroalgae Padina boergesenii,Colpomenia sinuosa, and Ulva sp. Other
protocols aiming to obtain polysaccharides also mentioned the use of
Soxhlet extractor as a pretreatment of the biomass to eliminate lipophilic
compounds before extracting the carbohydrates. For example, Soxhlet
extraction was used to eliminate lipids from Macrocystis pyrifera for
bioethanol production (Camus et al., 2016) and mixtures of methanol and
acetone were employed in a Soxhlet apparatus to pretreat red macroalgae
Chondracanthus chamissoi and Gelidium lingulatum aiming to eliminate
pigments and lipids in the process of extraction of agar (Véliz et al., 2018).
Soxhlet techniques have also been used in the field of analytical
chemistry to develop methods determine contaminants from a wide
variety of samples (Luque de Castro and Priego-Capote, 2010). For
instance, Soxhlet has been used as a reference method to compare the
efficiency of other novel protocols when extracting and analyzing
polychlorinated biphenyls contaminants (Crespo and Yusty, 2005) and
alkanes (Crespo and Yusty, 2006) from macroalga Undaria pinnatifida.
The technological improvements of this technique such as automated
Soxhlet were used in analytical methods approved by the Association
Official Analytical Chemists (AOAC) for the analyses of fat in several
food products, including meat (AOAC 991.36), forage, feed, and cereal
grains (AOAC 2003.05 and 2003.06) (Luque de Castro and
Priego-Capote, 2010). Moreover, automated extractors have been recently
used to obtain lipids from multiple matrices. Santos-Ballardo et al. (2015)
extracted lipidic compounds from algae Tetraselmis suecica using an
automated Soxhlet apparatus with n-hexane as extraction solvent.
The scientific literature on the application of ultrasounds coupled
to Soxhlet extraction is scarce. Ultrasound-assisted Soxhlet obtained
promising results when determining the total fat content in

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14 Sustainable seaweed technologies
oleaginous seeds (Luque-Garcıa and De Castro, 2004). The application
of ultrasounds decreased significantly the number of Soxhlet extraction
cycles needed for the quantitative determination of fat, reducing by half
the extraction times required when using the conventional Soxhlet
apparatus (Luque-Garcıa and De Castro, 2004). Similarly, the efficiency
of the Sono-Soxhlet apparatus was higher when extracting oil from dried
olives while maintaining the quality of the extracted products (Djenni et
al., 2013).
5PROSPECTS AND FUTURE TRENDS OF
CONVENTIONAL TECHNOLOGIES
Currently, the development of extraction procedures poses several
challenges as these techniques should be faster and more efficient than
previously available protocols, while reducing the use of organic solvents
(Herrero and Ibañez, 2018; Herrero and Ibáñez, 2015; Tiwari, 2015).
However, conventional technologies are still being used to date and in
some cases are considered as the techniques of choice for several
applications. Steam distillation is recognized as the standard method to
extract essential oils from citrus peel according to the current ISO and
AFNOR standards (Chemat and Boutekedjiret, 2016); and automated
Soxhlet has been used by the AOAC for the development of official
methods of fat analyses in meat (AOAC 991.36), forage, feed, and cereal
grains (AOAC 2003.05 and 2003.06) (Luque de Castro and
Priego-Capote, 2010).
Conventional extraction protocols are generally very time consuming
and require large volumes of toxic organic solvents, raising safety
concerns for the workers and consumers exposed to these chemicals
(Tiwari, 2015). These safety concerns together with the new trends in
analytical chemistry toward more sustainable and green extraction
protocols are the main drivers of innovation to develop conventional
extractors. The combination of innovative and conventional technologies
has shown promising results when developing novel technological
designs. The use of microwaves or ultrasounds combined with steam
distillation or Soxhlet extractors achieved excellent results by reducing
the time and energy consumption of the original extraction protocols.
The incorporation of novel technologies resulted in the successful
development of commercially available equipment, including novel
distillation units such as microwave hydrodistillation, solvent-

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Conventional extraction techniques: Solvent extraction 15
free microwave extraction, microwave accelerated steam distillation,
microwave steam distillation, microwave hydrodiffusion, and gravity and
microwave steam diffusion (Chemat and Boutekedjiret, 2016); and novel
Soxhlet apparatus, including the ultrasound-assisted Soxhlet,
Sono-Soxhlet, and Soxwave-100 (Djenni et al., 2013; Luque-Garcıa and
De Castro, 2004).
Conventional technologies such as Soxhlet are currently considered as
a reference method to compare the performance of new solid-extraction
procedures; and as mentioned previously, these techniques are still the
method of choice for certain analyses (Luque de Castro and
Priego-Capote, 2010; Wang and Weller, 2006). The shortcomings of each
technology are currently being addressed by automating the extraction
or incorporating external energy sources such as innovative technologies.
These modifications of the conventional apparatus aiming to develop
greener extraction protocols by reducing the time, energy, and solvents,
will guarantee the continued use of these technologies by adapting the
equipment to the new technological trends and current needs of the
industry.
ACKNOWLEDGMENTS
This research was supported by BEACON SFI Bioeconomy Research Centre, which is
funded by Ireland's European Structural and Investment Programmes, Science Foundation
Ireland (16/RC/3889) and the European Regional Development Fund. Marco
Garcia-Vaquero works in TEAGASC within the project EnhanceMicroAlgae funded by
the INTERREG Atlantic Area, European Regional Development Fund [project number:
EAPA_338/2016].
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FURTHER READING
García‐Vaquero, M., 2019. Seaweed proteins and applications in animal feed. In: Novel
Proteins for Food, Pharmaceuticals and Agriculture: Sources, Applications and
Advances. pp. 139–161.