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Scientific African 19 (2023) e01585 
Contents lists available at ScienceDirect 
Scientific African 
journal homepage: www.elsevier.com/locate/sciaf 
A review of modern and conventional extraction techniques 
and their applications for extracting phytochemicals from 
plants 
Chibuye Bitwell a , b , c , ∗, Singh Sen Indra 
b , Chimuka Luke 
c , 
Maseka Kenneth Kakoma 
b 
a Department of Chemistry, School of Mathematics and Natural Sciences, Mukuba University, PO Box 20382, Itimpi Campus, Kitwe, 
Zambia 
b Department of Chemistry, School of Mathematics and Natural Sciences, The Copperbelt University, PO box 21692, Kitwe, Zambia 
c Molecular Sciences Institute, School of Chemistry, University of Witwatersrand, Johannesburg, South Africa 
a r t i c l e i n f o 
Article history: 
Received 18 August 2022 
Revised 2 February 2023 
Accepted 8 February 2023 
Editor: DR B Gyampoh 
Keywords: 
Phytochemicals 
Solvent extraction 
Modern extraction techniques 
a b s t r a c t 
For centuries, phytochemicals have been of immense value to communities worldwide. 
These metabolites have been used in healthcare systems as medicines to treat various 
diseases. Further, phytochemicals are used as lead compounds in the synthesis of drugs. 
The extraction of compounds from plant materials is the cornerstone of natural product 
research. There has been a relentless endeavor to discover better extractive methods. In 
the same vein, several promising modern green extraction methods such as supercritical 
fluid, ultrasound, accelerated solvent, microwave, enzyme-assisted extraction methods are 
gaining significance. This review describes and discusses the various extraction techniques 
used to obtain the phytochemicals from different plant parts. These extraction techniques 
include the conventional solvent-based and the more robust modern and green extraction 
techniques. The review critically analyses the extraction conditions, optimized situations, 
advantages, and disadvantages of these extraction techniques. The review includes the re- 
cent applications of these extraction techniques. The review will propel advanced research 
and applications in the extraction process, a significant and integral component of natural 
products research. 
© 2023 The Author(s). Published by Elsevier B.V. on behalf of African Institute of 
Mathematical Sciences / Next Einstein Initiative. 
This is an open access article under the CC BY-NC-ND license 
( http://creativecommons.org/licenses/by-nc-nd/4.0/ ) 
 
 
Introduction 
Many communities worldwide have been using medicinal plants in their healthcare systems from time immemorial. As 
far as Africa is concerned, medicinal plants are still a principal component of the traditional healthcare system and may be
the earliest and the most robust of all curative entities [1] . In most of rural Africa, traditional practitioners’ prescriptions
of plant remedies are the most readily available and affordable medicinal drugs accessible to the community and, every so 
∗ Corresponding author at: Department of Chemistry, School of Mathematics and Natural Sciences, Mukuba University, PO Box 20382, Itimpi Campus, 
Kitwe, Zambia. 
E-mail address: bchibuye@mukuba.edu.zm (C. Bitwell) . 
https://doi.org/10.1016/j.sciaf.2023.e01585 
2468-2276/© 2023 The Author(s). Published by Elsevier B.V. on behalf of African Institute of Mathematical Sciences / Next Einstein Initiative. This is an 
open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ) 
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C. Bitwell, S.S. Indra, C. Luke et al. Scientific African 19 (2023) e01585 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
often, the only treatments available. Studies have been performed worldwide to establish the efficacy of plant remedies, and 
some of the promising potential results have consequently led to the synthesis of plant-based medicines [2] . It is estimated
that globally, the market value for all medicinal plant commodities transcends USD 100 billion per year [3] . In present times,
despite the phenomenal growth in the development of synthetic drugs in pharmaceutical chemistry, almost 75 to 80% of the 
global population use herbal drugs as medicines, mostly in third world countries, for primary health care because of their 
better tolerability with the human body and minor side effects, and also easier availability [3] . It has been documented
those natural products are used to develop an estimated 44% of all novel drugs, primarily as lead compounds, to develop
and prepare partially synthetic medicines [4] . Moreover, there has been a paradigm shift to using plants to discover novel
lead molecules and drugs. 
Research on finding novel drugs in medicinal plants involves screening the plant extracts for new compounds and then 
conducting biological activity tests. Suspected new molecules or bioactive compounds are then isolated and purified for 
molecular structure elucidation and further pharmacological or toxicological tests [5] . The research typically involves the 
following steps: Firstly, plant materials are harvested from their natural environments. Secondly, using well-preserved leaves, 
flowers, or fruits, the plant species is identified by a botanist at a herbarium. Thirdly, plant parts of interest such as roots,
stems, backs, leaves, or fruits are treated with an appropriate solvent to extract the phytochemicals. The extract is then 
concentrated by processes that aim to remove the solvent. Then, the extract is subjected to chromatographic techniques 
to isolate and purify the bioactive compounds. Further, the isolated compounds may be subjected to various spectroscopic 
analyses such as UV/Vis, IR, carbon and proton NMR, and mass spectrometry for structure determination. After that, chemical 
methods may be used for pharmacological and toxicological testing. Finally, the elucidated bioactive compounds may be 
synthesized or semi synthesized. 
Extraction is an essential feature in natural product research. There is relentless stride going on to improve and discover 
better extractive techniques having better efficiency and cost-effectiveness. This review comprehensively discusses a wide 
range of conventional and modern extraction techniques, their optimization conditions, and their comparative advantages 
and disadvantages. A vast array of recent applications of these techniques have also been critically analyzed. This literature 
analysis will be beneficial for advancing the current and discovering novel extraction techniques. 
Bioactive compounds 
A plant’s life produces two categories of vast phytochemicals [6] . In the first category are the primary metabolites. These
are required for a plant’s normal growth and development. They include nucleic acids, carbohydrates, fatty acids, proteins, 
and the molecules present in all plants for their growth and development, such as growth regulators and cell wall com-
ponents. The second category is the secondary metabolites required for the plant to enhance its ability to survive in its
environment and overcome threats in its niche. In other words, secondary metabolites are compounds produced in a plant 
that enables a plant to adapt to its local environment. It is worth mentioning that secondary metabolites have various func-
tions in plant physiology and biochemistry. Any plant species propagating in an unfavorable niche, such as tepid and aquatic 
tropical forests, will strive to preserve itself by producing biomolecules that may have insecticide, fungicide, antibacterial, or 
antiviral properties [7] . However,However, degradation of phenolics ensued at high temperatures (above 160 °C), leading to reduced 
antioxidant capacity [127] . Furthermore, during the extraction of polyphenols from lotus seedpods, PHWE demonstrated that 
the antioxidant and antiproliferative activity of polyphenols were positively correlated with the polyphenols concentration 
[128] . Finally, selective extraction of phytochemicals with particular biological capacity can also be attained by using PHWE. 
For example, in comparison with conventional ethanol extraction, PHWE proved to be a much more effective technique for 
selectively obtaining phenolic compounds with high antioxidant capacity from k ̄anuka leaves [129] . 
Extraction time and temperature have a bearing on both the preservation and yield of the phytochemicals. For example, 
even if the recovery yield of flavanols and alkaloids from cocoal shells was enhanced by elevating the temperature and 
extraction time, prolonged extraction times and higher temperatures deteriorated the phytochemicals extracted [130] . In the 
same vein, it was observed that the yield of xylan from quinoa stalks plummeted at elevated temperatures due to molecular
degradation [131] . On the contrary, it was observed that the extraction yield of flavonoids from Bidens pilosa increased in
proportion to the increase in temperature [132] . 
A study conducted at a moderate temperature of 80 °C observed excellent recovery of polyphenols and tannins, but a 
substantial decrease of polyphenols yield at elevated extraction temperature of 150 °C. Besides, a significant reduction in 
the antioxidant activity of the polyphenols recovered at a high temperature of 150 °C was observed [133] . This observation
could be attributed to the degradation of the phytocompounds and the formation of other reaction products. The following 
Table 3.6 contains some of the recent applications of PHWE. 
The efficiency of PHWE can be significantly enhanced when used in combination with other extraction techniques. For 
example, the efficacy of recovering hesperidin and narirutin from Citrus unshiu peel by-products was increased by using 
14 
C. Bitwell, S.S. Indra, C. Luke et al. Scientific African 19 (2023) e01585 
Table 3.6 
Some recent applications of PHWE. 
Plant specie (Botanical or common name) Plant part 
Plant major compounds 
extracted Optimum conditions Refs. 
Moringa oleifera (MO) Leaves Vitamin C and phenolic 
compounds (kaempferol, 
quercetin) 
Temperature of 91 °C, extraction time of 
60 min, and flow rate of 0.3 mL/min 
[119] 
Moringa oleifera Leaves essential compounds 
(flavonols) 
Temperature of 100 °C, a flow rate of 
1.0 mL/min 
[120] 
Cannabis sativa Seeds Cannabinoids Temperature of 100 °C, extraction time of 30 
min 
[121] 
Cannabis sativa Seeds Cannabinoids Decarboxylation temperature of 149.9 °C, 
decarboxylation time of 40 min 
[121] 
Stevia rebaudiana Bertoni Leaves diterpenic glycosides Temperature of 160 °C, 10 mins duration and 
pressure of 10.34 MPa 
[122] 
Thymus vulgaris Leaves Polyphenolic compounds Temperature of 100 °C and extraction time of 
5 min 
[123] 
pistachio (Pistacia vera L.) Hulls Phenolic compounds Temperature range of 110–190 °C, pressure of 
6.9 MPa and 4 ml/min flow rate 
[124] 
Grape Pomace Phenolic compounds Temperature of 100 °C and natural deep 
eutectic solvents 
[125] 
defatted orange Peel Flavanones Temperature of 150 °C, and flowrate of 
10 mL/min. 
[126] 
T. montanum aerial parts Phenolics Temperature of 160 °C and pressure of 10 bar [127] 
Lotus Seedpods Polyphenols Temperature of 140 °C, extraction time of 
20 minutes, and liquid-solid ratio of 70 mL/g 
[128] 
K ̄anuka Leaves Phenolic compounds Temperature of 170 °C, extraction time of 
20 min and 15 g/L sample. 
[129] 
Cocoa Shell flavanols and alkaloids Pressure of 10.35 MPa and temperature range 
of 60 - 90 °C at static times range of 5 to 
50 min 
[130] 
Chenopodium quinoa Willd Stalks saponins, xylan and 
cellulose 
Temperature of 80 °C [131] 
Bidens pilosa Leaves and 
stems 
flavonoids Temperature of 150 °C, flow rate of 
5.0 ml/min, and extraction time of 10 min 
[132] 
Chestnuts Shells polyphenols and tannins Temperature of 80 °C and extraction time of 
10 min 
[133] 
Citrus unshiu Peels Flavonoids Temperature range of 110–190 °C and 
extraction time range of 3–15 min 
[134] 
 
 
pulsed electric field combined with subcritical water extraction [134] . Generally, this technique affords better products, is 
less time-consuming, utilizes less energy than steam distillation. The lone features of water as a preferred extractant in 
PHWE arises from it being eco-friendly, a universal solvent, appropriate for recovering thermal-labile phytocompounds, and 
readily available. 
Conclusion 
There is considerable attention toward natural product research globally. The extraction of bioactive compounds is a crit- 
ical step in natural product research. It has been the bottleneck in accelerating the screening of more and more products.
Currently, extraction involves separating medicinally active molecular components of plant tissues from the inert compo- 
nents by using traditional solvent extraction techniques or the standard modern and green extraction procedures. The ex- 
traction technique’s choice is crucial as it determines the reliability and quality of subsequent analytical activities. The main 
focus of extraction is to achieve economic viability, environmentally friendliness, shorter extraction time, and better yields 
of bioactive compounds without compromising the biological activities. Reports suggest that modern techniques have mani- 
fold advantages over conventional techniques. The conventional extraction techniques are characterized by longer extraction 
time, more solvent requirement, risking bioactivity, and less yield. The modern techniques offer many advantages like re- 
duced required time, less solvent demand, better preservation of biological activities, better yields, and less energy demand. 
Although it is complex to conclude due to a huge number of studies, the choice of extraction technique hinges on the plant
matrix, targeted phytochemicals, economic viability, and environmental impacts. 
Outlook 
There is a need for deliberate research focused on optimizing and standardizing the extraction conditions of modern 
extraction techniques for specific classes of phytochemicals. Exploring the most appropriate extraction techniques specific to 
various plant species would be interesting. It is required that the current extraction techniques be improved and new high- 
resolution and more effective techniques be introduced. These developments, it is hoped will lead to enhanced recovery of 
15 
C. Bitwell, S.S. Indra, C. Luke et al. Scientific African 19 (2023) e01585 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
novel phytocompounds from natural sources, especially plants. Further studies are vital to enhance our understanding of 
extraction techniques and mechanisms. 
Notes 
This work is part of the of the doctoral dissertation by Chibuye Bitwell and supervised by Professor Indra Sen Singh,
Professor Maseka Kenneth Kakoma and Professor Chimuka Luke. The study focussed on phytochemical studies and metal 
analysis of some medicinal herbs used in the traditional healthcare system in Zambia and elsewhere. 
Declaration of Competing Interest 
All authors declare that they have no conflict of interest. 
Acknowledgments 
Authors wholeheartedly acknowledges the support rendered by the Ministry of Education of the Republic of Zambia, Cop- 
perbelt University – Africa Centre of Excellence in Sustainable Mining (CBU – ACESM) and the Mukuba University, without 
which this study would not have been achievable. 
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	A review of modern and conventional extraction techniques and their applications for extracting phytochemicals from plants
	Introduction
	Bioactive compounds
	Conventional extraction techniques
	Maceration
	Digestion
	Infusion and percolation
	Decoction
	Soxhlet extraction
	Disadvantages associated with conventional extraction techniques
	Modern extraction techniques
	Accelerated solvent extraction (ASE)
	Microwave-assisted extraction
	Ultrasound-assisted extraction, UAE (sonication extraction)
	Supercritical fluid extraction (SFE)
	Enzyme-assisted extraction (EAE)
	Pressurized hot water extraction (PHWE)
	Conclusion
	Outlook
	Notes
	Declaration of Competing Interest
	Acknowledgments
	Referencesassuming the leaves of a plant display no signal of invasion, they may possess defensive
bioactive molecules in opposition to insects and microorganisms. The roots may often produce antifungal phytochemicals 
due to the rich nature of pathogenic fungi in the soil. These secondary metabolites may also exhibit antifungal reactions 
in opposition to human pathogenic fungi [8] . Therefore, due to the diverse functions that plant phytochemicals possess in
plant cells, these molecules are of unique interest to pharmacologists and biochemists. Suffice to say that specific secondary 
metabolites are bioactive compounds evoking pharmacological or toxicological effects on animals and humans. Bioactive 
phytochemicals can be broadly classified as terpenes and terpenoids, alkaloids, and phenolic compounds [6–8] . Their spe- 
cific structural characteristics hinge on the reaction pathway in which they were bio-synthesized. The extraction of bioactive 
compounds from plant sources is achieved through various steps are presented in Fig. 1.1 . 
Conventional extraction techniques 
Maceration 
Maceration is a simple extraction method that involves soaking the plant prepared raw material in a coarse or powder 
form in a solvent of interest at room conditions for at least three days with intermittent agitation [9] . After the extraction
is completed, the mixture is strained either through sieves or a net with tiny holes. Subsequently, the marc is pressed, and
the liquid extract is cleaned using either filtration or decantation after standing. Maceration is preferably carried out in a 
stoppered container to minimize solvent loss through evaporation. It is undesirable to obtain an already concentrated ex- 
tract through evaporation of the solvent during the extraction process. The product is concentrated frequently by the use of 
vacuum evaporation. It is crucial to select an appropriate solvent in the maceration as the solvent will delineate the phyto-
chemicals classes salvaged from the samples. The solvent could also enable the extraction of thermolabile phytochemicals. 
The procedure has the underlying disadvantage of low efficiency and long duration of extraction [9] . However, optimized 
conditions may attribute significant efficiency to this technique as high phenolic compounds, and anthocyanins yield were 
obtained from chokeberry [10] . On the other hand, a study on C. cajan leaves to extract flavonoids using microwave-assisted,
2
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Fig. 1.1. Scheme of steps involved in extraction of phytochemicals from plant sources. 
3
C. Bitwell, S.S. Indra, C. Luke et al. Scientific African 19 (2023) e01585 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
reflux, ultrasound-assisted, and maceration extractive methods observed that the maceration techniques afforded the lowest 
yield [11] . Flavonoids have also been extracted using maceration from rhizomes of turmeric using nonionic surfactant Triton 
X-100 at a temperature of 35 °Cat neutral pH, from fruits of Arbutus unedo L. at a raised temperature of 79.6 °C in 3.7% di-
luted ethanol, and from leaves of Ficus carica and Euphorbia neriifolia using 75% concentrated ethanol at room temperature 
[12–14] . In these studies, the type of solvent used was based on the polarity of the phytochemicals extracted. For instance,
Triton X-100, which is nonionic but has a hydrophilic side chain, was used to extract less polar flavonoids, whereas the
more polar ethanol, or a mixture of ethanol and water was used to extract more polar flavonoids Further, Polyphenols, such
as anthocyanins have been extracted from dried fruits of chokeberry using 50% ethanol as solvent [15] . 
Digestion 
Digestion is an extractive method similar to maceration and uses slight warming in the extraction process [9] . Care is,
however, exercised to avoid the temperature altering the bioactive phytochemicals of given plant material. Therefore, there 
is increased efficiency in using the extraction solvent due to warming. Mostly temperatures are kept in the range of 35 to
40 °C but may be increased to a maximum of 50 °C for tougher plant materials such as barks and materials containing
dismally soluble phytochemicals. During extraction, desired plant parts are introduced in a container with the appropriate 
solvent pre-heated to the indicated temperatures. The optimum temperature is maintained for a period that may range from 
half an hour to 24 h with shaking the container at regular intervals [9] . 
Infusion and percolation 
Infusion is described as a dilute solution of easily soluble constituents of the plant material. It is an extraction technique
in which the plant material is immersed in boiling solvent, particularly water, and left to stand in a stoppered container for
about 15 min, after which time the extract (tea) is poured off and separated from the marc using a filter [9] . Tea may be
considered as the best example of an infusion. For example, Caffeine has been extracted from dried crushed leaves of tea
brands alokozay, lipton, tapal, and tetley at brewing times ranging from 2 to 30 min within the temperature range of 30
to 90 °C [16] . Further, phenolic compounds were extracted from fruits of Tilia cordata at an optimal temperature of 95 °C
[17] . It has to be noted that some infusions are prescribed to treat health issues such as diarrhea, bronchitis, and asthma.
For instance, antioxidants; phenols, and flavonoids have been extracted from rhizomes of various gingers in boiling water 
for 10 min [17] . Another method of interest similar to infusion but more efficient than maceration is percolation. 
Percolation is the most popular procedure for preparing fluid extracts such as tinctures. Percolation means "to pass a 
liquid through a solid material drop by drop." During percolation, the solvent, commonly ethyl alcohol, is slowly passed 
through the plant material, gradually packing itself with phytochemicals, and is gradually propelled down by another fresh 
solvent added from the top [9] . Before introducing plant material into the percolator, it must be carefully shredded, not
making the particles too small. If particles are too fine, it will complicate separating the fine particles from the extraction
solvent. Consequently, the extract would be cloudy with residue settling at the bottom of the percolator. Nonetheless, it is 
appropriate to moisten the plant matrix with the extraction solvent, enabling the plant cells to elongate for smooth diffusion 
of phytochemicals into the extraction solvent [ 9 , 17 ]. 
After the plant material is inserted into the percolator, the extraction solvent is poured in from the top and percolates
through the plant material at a speed determined by the nature of the plant material subjected to extraction. The solvent
flow rate should not be excessive to allow time for solvent penetration into plant cells and extract the constituent phy-
tochemicals. Nevertheless, the solvent percolation rate should not be too slow, leading to more solvent consumption for 
complete extraction. In general, for 1 kg of plant material, the solvent flow rate should be about 5 mL per minute. 
The choice of extraction solvent depends on the chemical attributes of the secondary metabolites being extracted. A 
water-alcohol solvent mixture is commonly utilized, resulting in extra efficient extraction because water hydrates plant walls 
as the alcohol is chemically similar to most active components extracts from the plant material. For example, Phenolics, 
particularly epicatechin, were extracted using 70% ethanol, and petroleum ether has been used to extract the antioxidants 
such as phenols and flavonoids [ 18 , 19 ]. Interestingly, apart from alcohol, inorganic aqueous solution of hydrochloric acid was
used to extract alkaloids from wild fruits by percolation [20] . However,the alcohol has the added advantage of preserving
the extract as it is a preservative. The extract is termed leachate. After the process has ended, the plant material is pressed
to recover the solvent absorbed residually, and the residual solution is added to the leachate (extract). Extraction ends upon 
elution of a colorless liquid, devoid of phytochemicals, from the percolator [9] . 
Decoction 
This extraction technique is useful for phytochemicals that do not decompose or modify with increasing temperature. 
During decoction, plant material is boiled in water for 15 to 60 min [9] . The duration of boiling will depend on the nature
of plant tissues and the phytochemicals being extracted. Ordinarily, delicate plant parts such as leaves, roots, flowers, and 
tender stems are boiled for 15 min. For instance, phenols and flavonoids have been extracted using decoction and infusion 
from fruits, rhizomes and leaves at 100 °C [ 19 , 21 ]. Instead, hard plant parts such as branches and tree barks can be subjected
4 
C. Bitwell, S.S. Indra, C. Luke et al. Scientific African 19 (2023) e01585 
 
 
 
 
 
 
 
 
 
 
 
to boiling for an hour. After boiling, the mixture is cooled and then strained, adding cold water to obtain the required
amount of solution. After the decoction process is completed, the mixture is filtered to obtain the liquid extract. 
The extract produced using the decoction technique is likely to have many undesirable products. It may also be noted 
that it is not the ideal method for thermolabile compounds. It has been reported that the bark extract of S. Cumini using
decoction as an extractive technique demonstrated significant antiglycation and antioxidant potential [22] . 
Soxhlet extraction 
Soxhlet extraction is a continuous extraction of phytochemicals using a hot solvent. The ground plant material is placed in 
a thimble (porous bag) made from either a firm filter paper or cellulose [9] . The thimble packed with ground plant material
is placed in the compartment of the Soxhlet paraphernalia. Extraction solvent such as ethanol or methanol is placed in the
bottom flask. The solvent is then heated and vaporized in the sample thimble, is next condensed in the condenser on top of
the apparatus, and then drips back, resulting in the extraction of phytochemicals. The enhanced yield is obtained compared 
to maceration-based extraction techniques. Fatty acids have been extracted using this technique from hemp seeds at 70 °C 
for eight hours, and phenolic compounds from leaves using 60% ethanol for two hours extraction time [ 23 , 24 ]. 
This extraction technique is quite efficient. Soxhlet extraction method afforded 38.21 mg g −1 of ursolic acid from tra- 
ditional Chinese medicine cynomorium. However, because of the higher temperature, this method risks the degradation of 
thermolabile compounds. Interestingly, a study comparing Soxhlet and maceration extraction methods discovered that the 
amounts of both polyphenols and alkaloid extracts decreased for the Soxhlet method [25] . 
Disadvantages associated with conventional extraction techniques 
Disadvantages associated with conventional solvent extraction techniques include prolonged extraction time, substan- 
tial amounts of solvents, and at times many extraction steps. Further, significant amounts of thermolabile phytochemicals 
turn out to be either decomposed or degraded during heating. However, these extraction techniques are still used to ex- 
tract fragrance-and-aroma oils from plants due to their simplicity [26] . Some recent applications of conventional Extraction 
Techniques are depicted in Table 2.1 . 
Modern extraction techniques 
Accelerated solvent extraction (ASE) 
This technique has gained considerable importance because of its benefits like low solvent demand, high output, and rel- 
atively less time consumed. The higher solvent temperature and pressure mark the ASE operations’ favorable condition. This 
technique is a more robust solvent extraction technique than either maceration or Soxhlet extraction. There are examples 
supporting significant ASE performance. For instance, it was found that ASE performed better at recovering lipophilic and 
hydrophilic phytochemicals from raspberry pomace compared with Supercritical Fluid Extraction (SFE). In ASE, the effects 
of temperature and extraction time on extraction yield were significantly less but recovered 25% lipophilic and hydrophilic 
compounds compared to the 15% yield in SFE [27] . In this technique, the extraction cell made of stainless steel is packed
with the sample, then filled with solvent, and placed between inert silica layers separated with cellulosic filter papers. The 
system is heated at an increased temperature and pressure for a preset time, the conditions favor extraction due to increased
diffusion coefficient and lowered viscosity. The extract is collected in vials and cell cleaned by pumping fresh solvent and 
nitrogen. The inert packing material prevents the plant matrix from forming aggregates that might block the system [28] .
Some recent applications of ASE are presented in Table 3.1 
To attain enhanced phytochemical recovery yields, critical ASE extraction conditions include but not limited to temper- 
ature, pressure, and extraction time. For example, the robustness of ASE was assessed during the extraction of cocaine and 
benzoylecgonine from coca leaves. The extraction technique was verified to be uniquely robust around an optimum temper- 
ature of 80 °C, the pressure of 20 MPa, and extraction time of 10 min [29] . Interestingly, temperature variation significantly
impacts the extraction efficiency of different bioactive compound classes differently. For exam ple, it was discovered that 
the highest phenolic acids content yield was achieved with high temperature, whereas lower temperatures afforded more 
efficiency in extracting high yields of flavonoids [ 30 , 31 ]. 
It appears that the critical extraction conditions may influence extraction efficiency individually or in combination. In 
some instances, a single parameter may affect extraction. As was the case during the recovery of carbohydrates and phenolic 
compounds from barley hull, pressure and extraction time were insignificant; the only temperature was found to influence 
the extraction yield of phytochemicals [32] . In other circumstances, some conditions may exhibit the combined influence 
of the extraction of phytochemicals. For example, during the ASE of steviol glycosides from stevia leaves, it was found that
temperature, extraction time, and the number of cycles substantially affected phytochemicals yield in a composite manner. 
At the optimum temperature of 100 °C, 4 min of extraction duration, and 1 cycle, an average of 91.8 ± 3.4% glycosides were
recovered. However, upon additional optimization of reducing the particle size of plant samples to less than 0.5 mm the 
experimental extraction yield surged to 100.8 ± 3.3% [33] . In addition, during the extraction of carotenoids from food ma- 
trices, time and temperature were found to have a significant effect on carotenoids’ recovery yield. The optimum conditions 
5 
C. Bitwell, S.S. Indra, C. Luke et al. Scientific African 19 (2023) e01585 
Table 2.1 
Some recent applications of conventional extraction techniques. 
Plant specie (Botanical or 
common name) Plant part 
Plant major compounds 
extracted Extraction technique Optimum conditions Refs. 
Curcuma longa L. 
(turmeric) 
Rhizomes Silybins 
(flavonolignans) 
Maceration-Mediated 
Liquid–Liquid 
Extraction 
2.8% (w/w) Triton X-100, at 35 °C 
and a pH of 7.0 for 2.0 h 
extraction time on an orbital 
shaker set at 150 rpm 
[12] 
Arbutus unedo L Fruits Flavonoid (catechin) Maceration Temperature of 79.6 ± 5.2 °C, 
Extraction time of 93.2 ± 3.7 min 
and 23.1 ± 3.7% of ethanol 
[13] 
Ficus carica Leaves Flavonoids Maceration Temperature of 25 °C, ethanol 
with concentration of 70%,and 
extraction time of 3 days 
[14] 
Euphorbia neriifolia Leaves Flavonoids Maceration 70% (v/v) ethanol [16] 
Aronia melanocarpa 
(chokeberry) 
dried fruits Polyphenols, 
anthocyanins 
Maceration 50% ethanol, Solid–solvent ratio of 
1:20 
[15] 
Hamelia patens dried leaves Phenolics (epicatechin) Percolation 1 L of 70% ethyl alcohol solvent [19] 
Syzygium cumini L. Leaves Antioxidants (phenols, 
flavonoids) 
Sequential Cold 
Percolation Extraction 
Method 
Extraction solvent 100 mL of 
petroleum ether, plugged with 
cotton wool, and placed on a 
rotary shaker at a rotation of 
120 rpm for the extraction time of 
24 h 
[20] 
Macleaya cordata (Willd) R Fruit Alkaloids Percolation 500 ml of 0.1 mol/L hydrochloric 
acid aqueous solution percolates 
through the column at 2 mL/min 
at 25 °C. 
[20] 
Tilia cordata Fruit Phenolics hot water infusion 50 mL of ultrapure water to 0.5 g 
of sample powder and brewing at 
95 °C for 1 h. The extracts then 
filtered through a 0.45 μm syringe 
filter 
[23] 
tea brands, namely 
Alokozay, Lipton, Tapal, 
Tetley and PG TIPS 
dried crushed 
leaves 
Caffeine Infusion Brewing time (2, 5, 10, 15, 20, 25 
and 30 min) and temperature of 
(90 °C and 30 °C) 
[24] 
Zingiber officinale var 
roscoe (elephant ginger), 
Zingiber officinale var 
amarum (emprit ginger), 
and (Zingiber officinale var 
rubrum) red ginger 
Rhizomes Antioxidants (phenols, 
flavonoids) 
infusion extraction 
method 
4 g of ginger powder was diluted 
in 100 mL of hot water ±100 °C 
water and waited for about 
10 min 
[22] 
Syzygium cumini L. Leaves Antioxidants (phenols, 
flavonoids) 
Decoction Extraction 
Method 
Temperature of 100 °C, extraction 
time of 30 min 
[25] 
Zingiber officinale var 
roscoe (elephant ginger), 
Zingiber officinale var 
amarum (emprit ginger), 
and (Zingiber officinale var 
rubrum) red ginger 
Rhizomes phenolic compounds decoction extraction 
method 
ginger powder was diluted and 
boiled in 100 mL of water at 
100 °C for ± 6 min 
[22] 
Cannabis sativa L. Hempseeds fatty acids Soxhlet extraction Extraction time of 8 h at a 
maximum temperature of 70 °C 
[23] 
Vernonia cinerea Leaves phenolic compounds Soxhlet extraction Extraction time of 2 h, 
feed-to-solvent of 1:20 g/mL and 
concentration of ethyl alcohol of 
60% v/v 
[24] 
 
 
 
were temperature of 60 °C, extraction duration of 15 min in three cycles. However, it was demonstrated that increasing the
amount of solvent through a number of cycles above three does not enhance further recovery of more carotenoids [34] . It
may suffice to add that in comparison to some other conventional and modern extraction techniques, ASE is very fast, very
efficient, replicable, green, more convenient, and does not require a lot of energy [33] . 
The phytochemical extraction yield is also specific to the nature of phytochemicals. Some studies suggest that the ex- 
traction conditions can have opposite effects on the extraction yield of two different types of phytochemicals. For instance, 
during the extraction of Beta-glucans and phenolic compounds from waxy barley using ASE, it was discovered that higher 
temperature favored lower extraction yield of the β-glucan, but higher recovery yield of phenolics. The lower extraction 
yield of β-glucan could be attributed to the fragmentation of the molecules at high temperatures [35] . 
The efficiency of the ASE technique also critically depends on the solubility of the phytochemicals in the solvent. Ordi- 
narily, high solubilities enhance the extent of extraction and, thus, the recovery yield of the phytochemicals. In this vein, 
higher yields of relatively nonpolar compounds such as butylidene dihydrophthalide, 4–hydroxy-4-methyl-2-pentanone, and 
6
C. Bitwell, S.S. Indra, C. Luke et al. Scientific African 19 (2023) e01585 
Table 3.1 
Recent applications of ASE. 
Plant specie (Botanical or common name) Plant part 
Plant major compounds 
extracted Optimum conditions Refs. 
Raspberry (Rubus idaeus L.) Pomace Phenolics Temperature of 70 °C, and pressure of 103 bar [27] 
coca Leaves Alkaloids (cocaine) temperature of 80 °C, pressure of 20 MPa, and 
extraction time of 10 min 
[29] 
Citrus sinensis), passion fruit (Passiflora 
edulis), watermelon (Citrullus lanatus), 
lettuce 
Isotonic 
beverage 
byproducts 
Phenolic acids and 
flavonoids 
Higher temperature (200 °C) favoured 
Phenolics and lower temperatures (63 °C) 
favoured flavonoids 
[30] 
Avocado Peel Phenolics Temperature of 200 °C [31] 
Barley Hull Phenolics and 
carbohydrates 
Temperature of 160 °C, pressure of 150 bar, 
flow rate of 0.005 L/ minute and extraction 
time of 2 min 
[32] 
Stevia rebaudiana Bertoni Leaves steviol glycosi des Temperature of 100 °C, extraction time of 
4 min and 1 cycle 
[33] 
Carrots Fresh orange 
carrots 
Carotenoids Temperature of 60 °C, extraction time of 
15 min in three cycles 
[34] 
Waxy barley Dehulled fiber β-glucans and 
phenolics 
Temperature of 151 °C, extraction time of 
21 min and 16% ethanol 
[35] 
Angelica (sinensis, acutiloba, gigas) Roots butylidene 
dihydrophthalide, 
4–hydroxy-4-methyl-2- 
pentanone,; and 
9,12-octadecanoic acid 
n-hexane solvent, extraction temperature 
(80 °C) pressure of 1500 atm, static cycle of 
2 min, static time of 10 min 
[36] 
Passiflora species Leaves Phenolic compounds 
(mainly flavonoids) 
Temperature of 80 °C, 64% (w/w) ethanol, five 
extraction cycles, 10 min per cycle, 3 g plant 
material 
[39] 
Alfalfa Leaves Pesticides Heating time of 5 min, static time of 10 min, 
solvent flush of 50%, 3 static cycles, time of 
120 s purge, temperature of 80 °C and 
pressure of 1500 psi. 
[40] 
Fructus schisandrae Fruit Four Lignans 
(schizandrin, 
schisandrol B, 
deoxyschizandrin, 
schisandrin B) 
87% ethyl alcohol, temperature of 160 °C, 
extraction time of 10 min, Pressure of 
1500 psi, flush volume of 60%, and one 
extraction cycle 
[41] 
Fennel (Foeniculum vulgare Miller) Dried seeds essential oils Temperature of 125 °C, 7 min extraction time, 
in 3 cycles 
[42] 
Microalgae Algal biomas Lipids Temperature of 125 °C, with 3 min extraction 
time at three cycles 
[43] 
Sorghum Bran phenolic compounds Temperature of 150 °C using 50 and 70% 
ethanol/water (v/v) 
[44] 
 
 
 
 
 
 
 
 
 
 
9,12-octadecanoic acid have been recovered from angelica roots using n-hexane at a temperature of 80 °C, the pressure of 
1500 atm, static time of 10 min, and static cycle of 2 min [36] . However, characteristics of identical solute and solvent polar-
ities such as a polar solute and solvent combination and nonpolar solute and solvent combinations are necessary for better 
yields [37] . It has also been reported that, mixture of solvents demonstrated better yields. Remarkably, there has been better
recovery of phenols when extracted using mixture of moderately polar solvents [38] , owing to the moderately polar nature
of phenols. In fact, phenols have an acidic nature more than alcohols due to the O − H bond’s polarity. The polarity in phe-
nols is enhanced by the presence of benzene ring, leading to the weakness of O − H bond, which facilitates the separation
of hydrogen ion. Therefore, when polar solvents are used, phenols are readily obtained. 
This technique optimizes both temperature and pressure for rapid extractions completing in as quickly as less than an 
hour time. For example, Phenolic compounds, mainly flavonoids, were extracted using ASE technique at an optimum tem- 
perature of 80 °C using 60% ethanol in less than an hour [39] . Similarly, a pesticide from alfalfa leaves was obtained, and
the extract was clear, colorless with low residual lipid content [40] . Furthermore, four lignans have been separated from 
the fruits of fructus schisandrae plant at an elevated optimal temperature of 160 °C in 87% concentrated ethanol [41] . The
versatile nature of the technique is supported asthis technique is also reported to extract compounds from marine sponges. 
[41] . 
We, however, must mention that the ASE technique is not always advantageous when compared with Soxhlet extraction 
in all aspects. For instance, during the extraction of estragole, an essential oil from the fennel plant, the Soxhlet technique
provided enhanced extraction robustness and greater amounts of phytochemicals were recovered compared to ASE. How- 
ever, the similar concentration of estragole were recovered in both techniques. The justification for using ASE for obtaining 
essential oils from fennel was its shorter extraction time and the utilization of a lower amount of solvent compared to the
Soxhlet technique. The suitable conditions for ASE during the extraction of essential oils from fennel were the temperature 
of 125 °C, extraction time of 7 min, and in 3 cycles [42] . Furthermore, ASE has been found appropriate for the extraction of
7 
C. Bitwell, S.S. Indra, C. Luke et al. Scientific African 19 (2023) e01585 
 
 
 
 
 
 
 
 
 
 
 
 
lipids as Soxhlet tends to oxidize lipids [43] . Lipid oxidation stems from continuous heating with a hot Soxhlet extraction
technique. ASE has been found suitable to obtain phenolic compounds from cereals. This technique is appropriate because 
most phenolic compounds in cereals tend to be highly bound to cell wall components and, therefore, are difficult to obtain.
The polyphenols were recovered from sorghum bran using ASE at an elevated temperature of 150 °C using a 50 and 70%
ethanol and water mixture, respectively [44] . 
In a nutshell, from the preceding applications of ASE, this extraction technique hinges mainly on the parameters such as 
solvents, raised extraction temperatures, and pressures and is easily optimizable for rapid extraction. In addition, the sol- 
vents used in ASE are those commonly utilized for conventional liquid extraction techniques such as Soxhlet. Further, ASE 
is largely quantitative for the extraction from reference materials of polychlorinated biphenyls, polycyclic aromatic hydro- 
carbons, and total hydrocarbons. Besides, there has been neither evidence nor claim for thermal deterioration of thermally 
labile compounds during the application of ASE. 
Microwave-assisted extraction 
Microwave-assisted extraction (MAE), also known as microwave extraction, is a recent way of extracting natural products 
that incorporate microwaves and solvents during the extraction process. The Microwave frequency ranges from 300 MHz to 
300 GHz. During the extraction process, microwaves heat the solvent and plant tissue, enhancing the kinetics of extraction. 
The microwaves heat the sample by directly impacting the polar molecules. The energy conversion from microwave to 
heat involves dipolar rotations. Heating is directly proportional to the dielectric constant of the solvents [45] . The viscosity
of the solvent affects the extraction process significantly as lower viscosity facilitates the dispersion of ions and hence 
solvation [46] . The extraction process involves the diffusion of solvents into the sample, subsequent separation of solute 
from the functional site, and finally releasing solutes to solvents. The technique is good at preserving the biological activities 
of the extracts. For example, the optimization of MAE in green tea extraction confirmed the improvement of the antioxidant 
activity of the phytocompounds and improved the total phenolic content and the targeted color quality of the extracts [47] .
Using the MAE technique, a variety of phytochemicals such as saponins have been obtained from seeds, Polyphenolic 
antioxidants from leaves, sterols from dried mushrooms, and flavonoids from leaves [48–50] . Notably, the phytochemicals 
such as flavonoids, polyphenols, and saponins extracted by MAE are polar compounds, and microwaves directly impact 
these compounds, rendering the extraction quite efficient. Several progressive and robust MAE instruments and methods are 
available, such as solvent-free microwave-assisted extraction (SFMAE) and pressurized microwave-assisted extraction (PMAE) 
[51] . 
The heating of dried plant material targets the minute infinitesimally small traces of moisture in plant cells. When mi- 
crowaves heat the moisture inside the plant cell, evaporation ensues. When evaporation occurs in dried plant cells, con- 
siderable pressure is developed on the cell walls, thereby pushing the cell walls from inside. The cell wall thus elongates
and eventually raptures, thereby exuding the bioactive components. This process increases the yield of phytochemicals [51] . 
Soaking the plant material in a suitable solvent before MAE further yields. The solvent further facilitates the hydrolysis of 
glycosidic (ether) bonds of cellulose into soluble fractions. The increased temperature also increases the phytochemical yield, 
enhancing solvent penetration into cellular walls. 
There is complete cell wall rupture in MAE as opposed to the heat–reflux extraction (HRE), as revealed by scanning
electron micrographs (SEM) of plant samples subjected to these extraction techniques. In HRE, a series of solvent cellular 
penetration and phytochemical solubilization bring out the cells’ bioactive compounds. On the other hand, phytochemicals 
are exposed to the solvent through cell rapture in MAE. There is desorption of active components from plant material in
MAE. The infinitesimally small traces of vapor occurring in plant glands and vascular tissues are heated, causing cell wall ex- 
pansion leading to phytochemicals flowing out of the cells. Therefore, the solvent and plant material dielectric susceptibility 
affect the microwave energy used in MAE. 
Microwave power and extraction time are the other parameters that impact extraction efficiency in MAE in addition 
to temperature. During the extraction of carotenoids from carrot waste, it was observed that both microwave power and 
extraction time were significantly useful in obtaining carotenoids from carrot waste [52] 
It has also been observed that polar solvents such as ethanol or water can promote solvent and sample mixture heating
due to the high dielectric constant [53] . Thus, it is advisable to use lower dielectric constant solvents to extract thermo-
labile requiring relatively lower temperatures. The plant material is submerged in microwave transparent solvent, such as 
n-hexane, to preserve thermolabile phytochemicals [53] . For instance, Curcuma oil which can degrade when extracted by 
conventional Soxhlet extraction has been extracted by MAE using the optimum conditions of 29.99 min extraction time, 
160 Wattage, and Curcuma powder and ethanol ratio of 1:20 w/v ratio obtaining 10.32% optimal yield [54] . MAE is a user-
friendly and versatile technique that even volatile compounds have been extracted at shortened time durations [55–57] . 
This is essential since most extraction techniques widely used in food extraction have the disadvantage of longer extraction 
times and are generally complex in operation. Table 3.2 presents recent applications of MAE in extracting phytochemicals. 
The MAE has many advantages compared to traditional solvent extraction techniques. MAE is rapid, uses a lesser solvent, 
is economical, and has a higher extraction rate. However, this extractive technique is more suitable for relatively smaller 
phenolic molecules, quacertines, isoflavines with their stability features at microwave temperature ranges [58] . The yield of 
triterpene from Centella Asiatica doubled as compared to the soxhlet method [59] . Optimum conditions of time and wattage
are critical, as evidenced in a study relating to Dioscorea hispida. [60] . 
8 
C. Bitwell, S.S. Indra, C. Luke et al. Scientific African 19 (2023) e01585 
Table 3.2 
Recent applications of MAE. 
Plant specie (Botanical or common name) Plant part 
Plant major compounds 
extracted Optimum conditions Refs. 
Sapindus mukorossiSeeds Saponins microwave power 460 W, solvent to material ratio 
8 mL/g, temperature 72 °C and extraction time 42 
min 
[46] 
Green tea Green tea bags Phenolics, flavonoids 
tannins 
Power of 350.65 W and extraction time of 5 min [47] 
Berberis asiatica Leaves Polyphenolic 
anti-oxidants 
microwave power of 500 W, sample to solvent 
ratio of 1:45 (g/ml) and 60% methyl alcohol 
[48] 
Agaricus bisporus L. (mushroom) fine dried 
powder 
Sterols (ergosterol) Extraction time of 19.4 ± 2.9 min, temperature of 
132.8 ± 12.4 °C and solid-liquid ratio of 
1.6 ± 0.5 g/L 
[49] 
Cajanus cajan Leaves Flavonoids 50 mesh particle size, 80% ethyl alcohol, ratio of 
1: 20 material/solvent, temperature of 60 °C, 4 
times cycle, 10 min extraction time, 500 W 
extraction power 
[50] 
Carrots Juice waste Carotenoids Microwave power of 165 W, extraction time of 
9.39 min and oil to waste ratio of 8.06:1 g/g 
[52] 
Curcuma longa L. (turmeric) Root curcuma oil Extraction time of 29.99 mi, extraction power of 
160 W and 1:20 w/v 
[54] 
Soy sauce. Sauce Volatile oils Extraction temperature of 70 °C for 30 min 
extraction time 
[55] 
Solanum melongena L. Eggplant peel phenolics, flavonoid 
and anthocyanin 
Power of 269.82 W, extraction time 7.98 min, 
liquid–solid ratio of 5.01 ml/g, ethanol 
concentration of 73.49%, and pH of solvent was 
3.06%, 
[56] 
Centella asiatica L. (Tiger grass) Leaves Phenolic Power of 450 W and extraction time of 60 min [57] 
Propolis propolis phenolics, quacertines, 
isoflavines 
70% ethanol, 800 W and 10 s power on, and then 
10 s power off irradiation cycle 
[58] 
Centella asiatica Leaf Triterpene Temperature of 75 °C, irradiation power of 600 W, 
4 extraction times and 4 irradiation cycles 
[59] 
Dioscorea hispida Tuber Alkaloid (Dioscorin) 85% ethanol, Power of 100 W and extraction time 
of 20 min 
[60] 
 
 
 
 
 
 
It has to be noted that MAE is most appropriate for obtaining phytocompounds that are lost en masse when conventional
methods are used. For example, in food processing, flavonoids are lost in remarkable amounts [61] . Thus, MAE is useful for
extracting flavonoids added as food additives during supplementation. Further, most extracts obtained using conventional 
techniques contain interferences when analysed chromatographically. Therefore, MAE is developed in such a way that inter- 
ferences are removed during extraction. When introduced into either GC or HPLC columns, the final extract mainly contains 
analytes with most interferences eliminated. 
Ultrasound-assisted extraction, UAE (sonication extraction) 
Ultrasounds are electromagnetic waves with higher frequencies than sound waves audible to the human ear. The range 
of ultrasound utilized is from 20 kHz to 20 0 0 kHz. It travels through a medium involving expansions and contractions
following the wave nature. The mechanical effect of acoustic cavitation from the ultrasound increases the surface area of 
contact between solvents and plant samples and the permeability of cell walls. The bubble formation, its growth and col- 
lapse is termed as cavitation. Some studies observed that frequency used can modify and favorably influence the extraction 
of compounds from the sample [62] . Some recent applications are depicted in Table 3.3 . 
Interestingly, a study observed the higher yields of phenolics at a lower frequency of 40 kHz than at 120 kHz [63] . Such
an observation prompts studies to evaluate ultrasonic parameters simultaneously to enhance and optimize extraction effi- 
ciency. A study using UAE reported phenols extraction from rhizomes with 75.3% ethyl alcohol over the extraction time of 
40 min higher yields compared to one with the solvent in context [64] . Ultrasonic-assisted extraction technique extracts 
bioactive compounds by relying on ultrasound’s mechanical action on plant cell walls [65] . The mechanical action of ul-
trasound enhances the surface contact between solvent molecules and the plant sample matrix. Thus, ultrasound modifies 
and disrupts plant materials’ physical and chemical characteristics, expedites the release of phytochemicals, and further 
reinforces the solvent system’s mass movement into plant cells [ 66 , 67 ]. The UAE technique was found to quicken the ex-
traction process, lowered the energy consumption, and increased the recovery of phytochemicals from annatto seeds. Most 
importantly, UAE, in this study of annato, efficiently preserved the extracted phytochemicals and thereby favouring the phy- 
tochemicals’ functional activities [68] . 
The UAE is a crucial extractive technique for extracting bioactive compounds, evident from its wide applications. Some 
phenolic compounds were reportedly extracted from strawberries [69] and oranges [70] , affording good results. Phenolic 
derivative and anthocyanine extractions using grape-peel using this technique have also been reported [71] . The efficiency 
9 
C. Bitwell, S.S. Indra, C. Luke et al. Scientific African 19 (2023) e01585 
Table 3.3 
Recent applications of UAE. 
Plant specie (Botanical or common name) Plant part 
Plant major compounds 
extracted Optimum conditions Refs. 
Pomegranate (Punica granatum L.) Peel, carpelar 
membranes 
surrounding 
edible part. 
Polyphenols Temperatures range of 50–60 °C and 37 kHz 
frequency, 
[62] 
grape pomace (Vitis vinifera L.) skins and 
seeds 
phenolics, flavonols Frequency of 40 kHz,150 W/L of US power 
density and extraction time of 25 min 
[63] 
Sparganii stoloniferum rhizomes Phenols 75.3% ethyl alcohol, extraction time of 40 min, 
solvent-to-material ratio of 19.21 mL/g 
[64] 
Malva sylvestris leaves Phenolics Temperature of 48 °C, Power of 110.00 W, and 
extraction time of 48.77 min 
[65] 
Annatto (Bixa orellana L.) seeds Polyphenols Frequency of 37 KHz and Ultrasonic power of 
320 W 
[66] 
peaches Phenolic compounds extraction temperature of 41.53 °C, ultrasonic 
power of 43.99% and extraction time of 
27.86 min 
[67] 
Strawberries Red 
strawberries 
Phenolics Temperature range of 85 – 90, over three 
cycles of 30 s time duration 
[68] 
Citrus sinensis Peel Polyphenols Amplitude of 70.89% solvent to solid ratio of 
40 ml/g and extraction time of 35 min 
[69] 
Grape (Vitis vinifera) Seeds Phenolics and 
Anthocyanins 
Temperature of 56.03 °C, 53.15% ethanol, and 
extraction time of 29.03 min 
[70] 
Boldo (Peumus boldus Mol.) Leaves alkaloids and 
flavonoids 
Temperature of 36 °C, sonication power 
23 W/cm 
2 and extraction time of 40 min 
[71] 
Lotus (Nelumbo nuficera Gaertn) leaves Flavonoids 70% ethanol, solvent to raw material ratio of 
35, and ultrasound time of 25 min. 
[72] 
Tilia cordata Inflorescence Flavonoids and 
phenolic acids 
Temperature of 60 °C, in three cycles, 
extraction time of 20 min and 80% methanol 
[73] 
Chenopodium quinoa (red quinoa), 
Glycine max (soybean), Lens culinaris 
(peeled red lenti) and Lupinus albus lupin 
seeds triterpenoid saponins Solvent either ethanol, water or ethanol: 
water (1,1, v/v) at a ratio of sample to solvent 
of 1:10 (w/v), Extraction time of 15 min, 
sonication output amplitude of 60%, 
Temperature during extraction process kept 
under 75 °C and extractions performed at 
least in duplicate 
[74] 
Libbys Select (pumpkins) Slices Phenolic compounds Temperature of 41.45 °C, extraction time of 
25.67 min and ultrasonic power of 44.60% 
[75] 
Brassica oleracea L. Var. Capitata f. Rubra 
(Red cabbage) 
leaves Anthocyanins ultrasonic output power of 100 W, pulse 
mode of 30 s ON: 30 s OFF, at temperature 
of15 °C for 90 min duration 
[76] 
Allium sativum L. (garlic), Zingiber 
officinalle L.(Ginger) and Curcuma longa L. 
(turmeric) 
Roots, 
rhizomes 
Curcumin, gingerol Extraction temperature of 70 °C [77] 
Cymbopogon martinii leaves Geraniol Ultrasound amplitude of 65%, ultrasound 
power of 60 W, and sonication time of 16 min 
[78] 
Orange Peel Carotenoids Ionic liquid, 1–butyl–3-methylimidazoliumchloride ([BMIM][Cl]) 
[79] 
common buckwheat sprouts Flavonoids Temperature of 56 °C and extraction time of 
40 minutes 
[80] 
Red grapes Wine lees Anthocyanins extraction time of 30.6 min and ultrasound 
power of 341.5W 
[81] 
 
 
 
 
 
of UAE is supported by a study reporting considerably less time of 30 min and far better yields than the maceration method,
which took 120 min and afforded lower yields [72] . Furthermore, The UAE method predominantly enhances the extraction 
speed and requires a relatively lower quantity of the solvent [ 73 , 74 ]. Thus, UAE is an extractive method of marked preference.
Using UAE, triterpenoid saponins were obtained from edible seeds at optimal sonication output amplitude of 60% [75] , 
Phenolic compounds from slices of pumpkins at reduced ultrasonic power of 44.60% [76] , and anthocyanins from leaves of
red cabbage using an ultrasonic output power of 100 W [77] . 
A highly significant attribute of UAE which merits emphasis is that it preserves the nature of compounds that degrade at
elevated temperatures. For example, carotenoids, phenolics, and vitamin C have been extracted from spices such as ginger, 
garlic, and turmeric without tempering with their chemical structure [78] . 
Additionally, UAE has been used in conjunction with other extraction techniques to shorten extraction time. For exam- 
ple, Ultrasound-assisted hydrotropic extraction was found to be a far more superior sustainable alternative than hydrotropic 
extraction owing to shortened extraction time and reduced hydrotrope concentration [9] . Further, the nature of the solvent 
used also impacts UAE. Using ionic liquids instead of conventional organic solvents assisted by ultrasound extraction im- 
proves the process. As an example, there was a fourfold surge in extraction yield of carotenoids from orange peels from
10 
C. Bitwell, S.S. Indra, C. Luke et al. Scientific African 19 (2023) e01585 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
7.88 ± 0.59 μg/g using acetone solvent to 32.08 ± 2.05 μg/g when ionic liquid, 1-n–butyl–3-methylimidazolium tetrafluo- 
roborate was used [79] . As is the case with ionic liquids, using eutectic solvents in UAE has enhanced the extraction yield
of phytocompounds. For example, deep eutectic solvents coupled with UAE efficiently recovered a yield of more than 97% 
flavonoids from common buckwheat sprouts [80] . Similarly, during the extraction of anthocyanins from wine lees, eutectic 
solvents proved to be more effective and efficient than acidified ethyl alcohol [81] . 
The reported extractions have revealed that ultrasound-assisted extraction is an environmentally friendly, green, and 
cheap technique compared to conventional techniques for extracting phytochemicals. The UAE has shortened extraction time, 
low energy requirement, and it also uses less amounts of solvents. UAE has a unique feature of recovering green extracts in
concentrated form without residual solvents, impurities, or defects. The extraction potential is drastically boosted through 
the utilization of ionic liquids as solvents. The minimized process times and temperatures are crucial for extracting thermo- 
labile phytochemicals such as phenolics, yet another attractive feature of this technique. 
Supercritical fluid extraction (SFE) 
The SFE technology has a broader application in extracting valuable compounds from various sources at a commercial 
scale. This technique has great potential to extract valued compounds from food products [82] . The SFE may be defined
by the changes in the temperature and pressure required to convert gas into a liquid, where two phases are not distin-
guishable. A Supercritical fluid substance shares both gas and liquid phases’ physical properties at its critical point [82] . The
critical region of a supercritical fluid is determined by temperature and pressure. At the critical point, which is achieved
above critical temperature-Tc and Critical pressure-Pc, gas and liquid phases become indistinctive. The technique involves 
the solubilization of extractable chemicals and their separation. The solvent dissolves chemicals in the sample while flowing 
through the packed bed. The solvent then leaves the extractor, and due to an increase in temperature and drop in pressure,
the extract becomes solvent free. 
Though it leans more towards the gaseous character, a supercritical fluid has the solvating properties of a liquid. Carbon 
dioxide, for instance, becomes supercritical at a temperature above 31.1 °C and 7380 kPa pressure. Several recent studies may 
be cited where supercritical carbon dioxide has been used. For example, Oil lipids (consisting mainly of glycerol-lipids, sterol 
esters, phospholipids) have been extracted from seeds at optimal Pressure of 80 MPa and temperature of 57 °C [83] , alkaloids
from seeds at a pressure of 27 MPa [84] , polyphenols, vitamins, anthocyanins, dietary phenolic compounds and carotenoids 
from leaves of sweet cherry at a pressure of 30 MPa [85] , essential oils from a herb at a Pressure of 30.4 MPa [86] , and
phenolics from potato peels at a pressure of 350 bar [87] . It is pertinent to emphasize the low extraction temperature in
SFE, which makes the technique uniquely suitable for extracting thermolabile phytochemicals. 
The use of Supercritical CO 2 (scCO 2 ) enhances extraction due to its strong solvation power for nonpolar phytochemicals. 
However, polarized phytochemicals tend to have low solubility in supercritical CO 2 . The solubility of polar phytochemicals 
in supercritical-CO 2 can be enhanced by adding a minute amount of ethyl alcohol or methanol, water, acetone, ethyl acetate, 
acetonitrile, and the like. This adjustment increases the phytochemical yield of the extract. For example, the application of 
ethanol as a co-solvent to scCO 2 enhanced the extraction yield of the main cannabinoids from industrial hemp residues 
by 30% [88] . Further, ethanol co-solvent enabled recovery of enhanced yields of phenolic compounds and flavonoids with 
an enhanced antioxidant capacity [89] . It has also been reported that ethanol-modified ScCO 2 led to the recovery yield of
extract, which correlated positively with antioxidant activity [90] . In addition, ethanol-water co-solvent was used to enhance 
scCO 2 extraction from Phyllanthus niruri [91] . Further, CO 2 has several advantages, including low toxicity, readily available, 
and being cheap. 
The supercritical CO 2 extraction method is applied to commercial extractions from natural resources. However, adjusting 
the temperature and pressure parameters is critical to enhancing the yield and uncompromised biological activities [ 92 , 93 ].
The higher temperature promotes the solubility of solutes in supercritical CO 2 , but it is suggested that due consideration
should be given for compromised temperature in the case of thermolabile molecules [94] . In the case of thermolabile phy-
tochemicals, keeping the temperature at unaltered low values while increasing the pressure helps the phytochemicals not 
degrade. For example, a significant yield of thermolabile phytochemicals was extracted from tomato skin at elevated pres- 
sure while keeping temperature, carbon dioxide flow rate, and extraction time constant [95] . To achieve maximum yield 
and maintain the product quality, a proper sample preparation with no trace of moisture is very significant as moisture may
adversely affect the yields in this extractive process [96] . Table 3.4 . shows recent applications of SFE. 
In comparison with conventional extraction techniques, SFE possesses several advantages. Firstly, SFE produces high 
yields and preserves the biological activities of extracts compared with conventional techniques such as Soxhlet. For ex- 
ample, apart from SFE recovering more oils from apple seeds than Soxhlet extraction, SFE extracts had higher oxidative 
stability than those extracted by Soxhlet [97] . In addition, more cannabinoidswith high antitumor activity for human cervi- 
cal cells were recovered from cannabis flowers than the low amount recovered using conventional extraction, which also had 
low antitumor activity [98] . Further, SFE has no residual organic solvents, is simplistic and rapid, efficiently operates, and 
produces high yields. Secondly, it is easy to enhance supercritical fluid’s dissolution characteristics by altering the pressure 
at a specific temperature. Thirdly, SFE is neither flammable nor explosive, a green extraction technique that does not cause 
environmental pollution. Fourthly, the solubility of polar phytochemicals can be enhanced by adding small amounts of en- 
trainers, which alters the extraction medium’s polarity, and it is economical to recycle the extraction medium in SFE. Finally, 
SFE can be used in combination with chromatographic spectroscopic or spectrometric techniques, among GC, IR, GC–MS, and 
11
C. Bitwell, S.S. Indra, C. Luke et al. Scientific African 19 (2023) e01585 
Table 3.4 
Recent applications of SFE. 
Plant specie (Botanical or common name) Plant part 
Plant major compounds 
extracted Optimum conditions Refs. 
Moringa oleifera (MO) 
Moringa peregrine (MP) 
Seeds Oil lipids (consisting 
mainly of glycerollipids, 
sterol esters, 
phospholipids) 
Pressure of 80 MPa and temperature of 57 °C [83] 
Lupinus mutabilis Sweet seeds Alkaloids Temperature of 323 K, a pressure of 27 MPa, 
using as a solvent supercritical carbon dioxide 
(scCO 2 ) and dilute ethanol solution 
[84] 
Prunus avium L. (sweet cherry) Leaves polyphenols, vitamins, 
anthocyanins, dietary 
phenolic compounds and 
carotenoids 
Temperature of 43 °C, pressure of 30 MPa, 
and extraction time 120 min, 
[85] 
Carum copticum Herb Essential oils Pressure of 30.4 MPa, temperature of 35 °C 
for a duration of 20 min, extraction time of 
30 min, 
[86] 
Solanum tuberosum (potato) Potato peels Phenolics Temperature of 80 °C, Pressure of 350 bar, 
20% methyl alcohol, flow rate of 18.0 g/min 
[87] 
Cannabis sativa L. (Hemp) stalks and 
leaves 
Phytocannabinoids 10% ethanol cosolvent, at 30 MPa extraction 
pressure and 45 °C extraction temperature 
[88] 
Radishes (Raphanus sativus L.) Leaves Phenolic compounds and 
flavonoids 
best results were the following combinations 
of temperature and pressure: 35 °C/400 bar 
and 40 °C/400 bar 
[89] 
L. rivularis stalks Phenolics Pressure of 40 MPa and 1% ethanol. [90] 
Phyllanthus niruri Plant gallic acid, corilagin and 
ellagic acid 
Ethanol–water co-solvent at two operating 
conditions (L1: 200 bar, 60 °C and L2: 
262 bar, 80 °C) 
[91] 
Tomato tomato skins Lycopene Temperature of 62 °C, and pressure of 45 MPa [92] 
Tomato Tomato sikns Lycopene Temperature of 100 °C, pressure of 40 MPa 
and flowrate of 1.5 mL/min. 
[93] 
Tomato Skin of ripen 
tomato fruits 
Lycopene and β-carotene Temperature of 60 °C, carbon dioxide flow 
rate of 2 mL/min and elevated pressure from 
350, 450 to 550 bar. 
[94] 
Longan fruit pericarp Phenolics Pressure of 500 MPa (UHPE-500) [95] 
Apples Seeds Oils Temperature of 40 °C, pressure of 24 MPa, 
flowrate of 1 L/h of CO2, and extraction time 
of 140 min 
[96] 
Acrocomia aculeate fruits Oil Temperature of 313 K and pressure of 22 MPa [97] 
Cannabis flowers Cannabinoids Temperature of 70 °C and pressure of 40 MPa [98] 
 
 
 
 
 
 
HPLC, to extract, isolate, and elucidate natural products rapidly and efficiently. Nevertheless, SFE has some underlying disad- 
vantages. These include the solubility of fat-soluble constituents, low solubility of water-soluble phytochemicals, it is difficult 
to clean the equipment, and the equipment is expensive, thereby rendering production uneconomical. 
Enzyme-assisted extraction (EAE) 
In certain plants, it is challenging to separate phytochemicals from the polysaccharide lignin network stabilized by hydro- 
gen bonding and hydrophobic interactions such as van der wall forces. Phytochemicals in their matrices remain dispersed in 
the cell cytoplasm and are inaccessible with the solvent extraction process. The bound phytochemicals in such samples are 
effectively released at high yields by pre-treating the plant material with specific enzymes [99] . These enzymes are added
during extraction to enhance phytochemical yield by breaking down cellular walls. Further, these enzymes hydrolyze carbo- 
hydrates such as cellulose and lipid bodies. The specific enzymes used include cellulase, pectinase, and amylase. Two main 
approaches that utilize enzymes during extraction are enzyme-assisted aqueous extraction (EAAE) and enzyme-assisted cold 
pressing (EACP). While the former technique has been used mainly to extract oils from diverse seeds, the latter has been
used to hydrolyze the plant’s seed cellular wall [99] . Using EAE, non-extractable polyphenols have been obtained from fruits 
of sweet cherry at the optimal temperature of 55 °C, carotenoids from sunflower petals at 40 °C, phenolics from citrus peels
at temperatures varying from 20 to 60 °C, lycopene from tomato peels at 30 °C, flavonoids from grapefruit peels at 50 °C,
and anthocyanins from Cacahuacintle Maize [100–104] . Some recent applications of EAE are presented in Table 3.5 . 
The EAE is utilized in conjunction with other extraction techniques as the enzymes make non-extractable phytochemicals 
accessible to the solvent and hence vulnerable for extraction. For example, the utilization of enzymes during microwave 
processing led to increased extractability of phenolic compounds from olive pomace at higher extraction temperature and 
faster heating strategy compared to low phytochemical recovery yield achieved by conventional solvent extraction using 
water [105] . Further, the sequential treatment of sisal waste with enzymes followed by ultrasound led to higher yields of
pectin compared to low yields of pectin obtained by other extraction techniques without the involvement of enzymes [106] .
12 
C. Bitwell, S.S. Indra, C. Luke et al. Scientific African 19 (2023) e01585 
Table 3.5 
Recent applications of EAE. 
Plant specie (Botanical or common name) Plant part 
Plant major compounds 
extracted Optimum conditions Refs. 
Prunus avium L (sweet cherry) Fruits 
(pomace) 
non-extractable 
polyphenols 
Temperature of 55 °C),enzyme concentration 
of 120 μL/g of sample residue, Sample to 
solvent ratio of 0.38 g sample/mL buffer, pH 
of 7.0, and extraction time of 5 h. 
[100] 
citrus plants (Yen Ben lemon, Meyer 
lemon, grapefruit, mandarin and orange) 
Citrus peels Phenolics Centrifugation temperatures varying from 20 
to 60 °C 
[101] 
Tomato Peel Lycopene Temperature of 30 °C, extraction time of 
3.18 h, enzyme load of 0.16 kg/kg, extraction 
solvents: acetone (99.7%), ethanol (99.5%) and 
hexane (99%) 
[102] 
grapes Fruit peels Flavonoids Temperature of 50 °C and pectinase enzyme [103] 
Cacahuacintle Maize Corn husks and 
cobs 
Anthocyanins pH of 5, and xylanases [104] 
olive Pomace Phenolic compounds Temperature of 50 °C and 2.0% of enzyme 
(tannase, pectinase and cellulase) 
[105] 
Sisal Sisal waste Pectin Temperature of 50 °C Celluclast loading of 
88 U/g and pH of 4.0 
[106] 
Seaweeds (Brown algae) Sargassum 
boveanum 
Phenolics pH of 4.5, and temperature of 50 °C [107] 
Licorice Roots glycyrrhizic acid Acetate buffer consisting of varied amounts of 
enzymes at the pH of 5.0 and temperature of 
45 °C for 60 min with agitation 
[108] 
Pomelo Peel Flavonoids 4.5% pectinase [109] 
Rosmarinus officinalis L. (Rosemary 
Leaves): 
Leaves Phenolics (antioxidants) Pretreating the plant material with 
pectinolytic enzymes for 1 h 
[110] 
Wine Lees Lees Phenolic compounds Temperature of 25 °C for 2 h at a pH of 4.0 [111] 
Ilex paraguariensis A (green yerba mate) Leaves Polyphenols Temperature of 50.0 °C, enzyme concentration 
of 168 FGB/100 g, reaction time of 120 min 
and pH of 4.50 
[112] 
Cotton cottonseeds Oil Pressure of550 bar, temperature range of 
70–80 °C and extracting time of 2–3 h 
[113] 
Astragalus membranaceus Herb polysaccharides enzyme amount of 3.0%, enzyme treatment 
time of 3.44days at a temperature of 56.9 °C 
and pH of 7.8 
[114] 
 
 
 
 
The enzyme concentration and pH vary depending on the enzymes’ nature and action. For instance, for carbohydrases, 
Viscozyme L, a multi-enzyme complex containing arabinase, cellulase, β-glucanase, hemicellulase, and xylanase, was used 
at optimum acidic pH of 4.5 and temperature of 50 °C in a 0.1 M acetate buffer to obtain the maximum extract yield
[107] . It has also been observed that enzyme concentration directly affects the yield of the extract. For example, increased
amounts of cellulase was found to enhance the licorice extraction yield [108] . Pretreatment of plant material of interest 
is followed by an extraction method after the enzymes detach the phytochemicals from plant material where they were 
extensively bound. For example, flavonoids were obtained from Pomelo peels by first treating the peels with 4.5% pectinase 
at various incubation times and afterward extracting the phytochemicals using ultrasound-assisted extraction method at a 
reduced optimal temperature of 30 °C [109] . In the same vein, pretreating of the plant material such as rosemary leaves with
pectinolytic enzymes for 1 h before a 24 h solid-liquid conventional extraction with 50% hydroethanolic solvent was found 
to be the optimum conditions for the extraction of rosemary leaves, providing an extract with higher radical scavenging 
activity of antioxidants than the corresponding extract without the enzyme pretreatment [110] . Another study demonstrated 
that enzymatic protein hydrolysis is an effective way of maximizing the extraction of phenolic compounds from Wine Lees 
and retrieving extracts with enhanced functionalities [111] . 
Several parameters have to be considered when using enzyme assisted extraction technique. For instance, using enzyme- 
assisted extraction from green yerba mate, using response surface methodology, polyphenols were extracted to determine 
the most optimal extraction conditions. Temperature, enzyme concentration, reaction time, and pH were independent vari- 
ables. The utilization of carbohydrases elevated the extraction of polyphenols from nearly 38.67% to 52.08%. The results 
revealed that all the independent variables were significant at the linear level, whereas pH and temperature were not sig- 
nificant at the quadratic level. Further, the combinations of enzyme and reaction time, pH and temperature, and enzyme 
and pH were found to be significant [112] . Table 5.5 presents some of the recent applications of EAE. 
Further research reports support EACP to be a preferred option for the extraction of bioactive molecules from oilseeds 
because of its nontoxicity [113] . Interestingly, the oil extract using EAE contained more fatty acids than those from conven-
tional techniques. A study on polysaccharide extraction involving glucose oxidase as an enzyme afforded more than double 
yield than enzyme free method [114] . Similarly, the yield of lycopene and carotenoid from tomatoes increased when ex- 
tracted using pectinase and cellulose [115] . The EAAE has the advantage of using water over other eco-harmful chemicals 
[116] . 
13 
C. Bitwell, S.S. Indra, C. Luke et al. Scientific African 19 (2023) e01585 
 
 
 
 
 
 
 
 
 
 
Understanding certain aspects of the plant material and the selected enzyme is critical to utilize the enzyme efficiently 
in the extraction. For the plant material, it is vital to understand its biochemical composition and morphology. These two 
aspects of the plant material should synergize with the selected enzymes’ catalytic properties, mode of action, and opti- 
mum operational conditions. Further, the combination of enzymes with modern extraction techniques such as ultrasonic, 
microwave, and supercritical fluid extractions can be developed to exploit the merits of both techniques in obtaining phyto- 
chemicals from plant materials. The utilization of the combined extraction techniques would lessen the extraction time and 
further improve the phytochemical yields. 
Pressurized hot water extraction (PHWE) 
This technique uses hot water extractant at enhanced pressure. It has drawn considerable attention as a likely alternative 
to conventional extractive techniques mainly because it is an environmentally favorable technique affording considerable 
yields [117] . The technique is based on the principle that the liquid state of water is maintained under pressure. A pressure
of 5 MPa ascertains a liquid water state between 100 and 250 °C. 
The PHWE has some advantages compared to conventional techniques. It takes a shorter extraction time, affords better 
quality extracts, and is a cheaper solvent. Several classes of compounds such as avoparcine, antioxidants, phenolics, and 
saponins, have been extracted using this technique [ 117 , 118 ]. Further, vitamin C, phenolic compounds [119] , and flavonols
[120] have been recovered from Moringa oleifera leaves at 91 °C and 100 °C, respectively. As for cannabinoids, they have 
been extracted from the seeds of Cannabis sativa at optimum temperatures of 100 °C for PHWE, and 145 °C for in situ
decarboxylation - Pressurised hot water [121] . 
The criteria for using PHWE are that water transforms above its atmospheric boiling point of 100 °C /273k, 0.1 MPa but
below its critical threshold of 374 °C/647k, 22.1 MPa into its nonpolar form, in which it dissolves nonpolar phytochemicals. 
Therefore, in PHWE, water acts as a universal solvent for both polar and nonpolar phytochemicals. Because of its ability 
to dissolve both polar and nonpolar phytochemicals, PHWE was used to recover both polar and nonpolar antioxidants, and 
steviol glycosides from Bertoni leaves at elevated temperature of 160 °C affording higher yields compared to lower yields at 
100 °C [122] . However, during the extraction of polyphenols from Thymus vulgaris, it was found that a lower temperature
of 100 °C was appropriate compared to higher temperatures such as 200 °C, which led to the degradation of phytochemicals
and impacted negatively on their antioxidant activity [123] . 
Compared to other solvents, water in PHWE has been found superior at recovering phytochemicals. For example, utiliz- 
ing water as a “green solvent” during the recovery of phytochemicals from pistachio, PHWE enabled the recovery of extracts 
with gallotannin and flavonol yields being remarkably higher than those extracted using aqueous methanol-based extraction. 
Further, it was discovered that the makeup of phenolic compounds obtained by PHWE was largely modulated by tempera- 
ture variation (110–190 °C) during extraction. Elevated temperatures increased the recovery yield of phytochemicals such as 
gallic acid from the pistachio hull matrix [124] . However, temperatures above 170 °C degraded the recovered phytochemicals. 
Natural deep eutectic solvents are good co-solvents that enhance the efficiency of subcritical fluid extraction. Using natural 
deep eutectic solvents, the utilization of subcritical water extraction enhanced the extraction yield of phenolic compounds 
from grape pomace at the optimum temperature of 100 °C [125] . Therefore, it is clear that using deep eutectic solvents
from natural sources for the utilization of subcritical water extraction seems to be a highly efficient and green extraction 
technique to obtain phenolic compounds from winemaking by-products. 
Additionally, PHWE is very green at preserving the bioactivity of extracts. For example, it was demonstrated that com- 
pared to conventional extraction techniques, PHWE is a highly efficient technique for the extraction of phytochemicals with 
high antioxidant activity [126] . Antioxidant activities were preserved for phenolics obtained from T. montanum aerial parts 
at medium temperature.