Asparagus Saponins: Chemical Characterization, Bioavailability and Intervention in Human Health
Amel Hamdi1,2*, Ana Jiménez-Araujo1, Rocío Rodríguez-Arcos1, Sara Jaramillo-Carmona1, Mokhtar Lachaal2 Najoua Karray Bouraoui2, Rafael Guillén-Bejarano1
1Phytochemicals and Food Quality Group, Instituto de la Grasa (CSIC), Spain
2Unité de Physiologie et de Biochimie de la réponse des plantes aux contraintes abiotiques, Tunisie
Submission: June 19, 2018;Published: July 10, 2018
*Corresponding author: Rafael Guillén-Bejarano, Phytochemicals and Food Quality Group, Instituto de la Grasa (CSIC), 41013 Seville, Spain,
Tel: 954611550; Fax: 954616790; Email: firstname.lastname@example.org
How to cite this article: Hamdi A, Jiménez-Araujo A, Rodríguez-Arcos R, Jaramillo-Carmona S, Lachaal M, et al. Asparagus Saponins: Chemical
002 Characterization, Bioavailability and Intervention in Human Health. Nutri Food Sci Int J. 2018; 7(1): 555704. DOI:10.19080/NFSIJ.2018.07.555704.
In the last years, there has been increasing interest in the research on saponins from food sources. Many epidemiological studies have pointed out their versatile health benefits. Since saponins are directly associated with human dietary ingredients and health, there is a need to evaluate their structure and function relationship. Asparagus spears are one of the main dietary sources of steroidal saponins.Most recent researches have focused on the health aspects of asparagus saponins for humans. Many asparagus saponins have cytotoxic and antitumor activities together with cholesterol lowering effect. This review highlights the structural features of saponins in asparagus, their beneficial roles in human health, and as well as their bioavailability and role on diet.
Asparagus is a perennial and monocotyledonous member of the Liliaceae family. It is grown for its edible stems (spears) which are consumed as a seasonal vegetable and are highly appreciated for their delicious taste, low energy content, and nutritional quality.
Now-a-days, there is an increasing scientific interest in studying the health benefits of asparagus not only for their nutritional properties, but also for their richness in bioactive compounds such as phenols, flavonoids, saponins, bioactive fiber, and sterols . Saponins play an important role on the organoleptic and functional properties of asparagus. Some studies have shown their hypocholesterolemic effect in both experimental animals and humans and are considered as potential nutritional supplements in the control of dyslipidemias and obesity [2,3]. Steroidal saponins from different varieties of asparagus showed cytotoxic and anti-tumor activities in different human cell lines [4,5]. However, the saponins present in edible plants of the genus Asparagus are not only responsible for the biological activity but can also contribute to the asparagus flavor; recently, saponins have been identified as the molecules responsible for the bitter taste of white asparagus[6,7].
Saponins are glycosylated compounds composed of two main parts: a water-soluble glycidic chain and a liposoluble structure (Figure 1). The non-sugar and sugar components are called aglycone and glycone, respectively. The aglycone portion is composed by a triterpenoid or steroidal backbone. L-arabinose, D- xylose, D-glucose, D-glucuronic acid, D-galactose, L-rhamnose and D-fructose are among the sugars constituents of saponins. The sugar moiety is linked to the aglycone through a covalent linkage at one or two glycosylation sites; in the first case the saponins are called monodesmosidic
and in the later bidesmosidic. In the monodesmosidic saponins
the oligosaccharide chain is generally attached at the C3
position, while bidesmosidic saponins have an additional sugar
moiety at the C26 or C28 position. The aglycone may contain
one or more unsaturated C-C bonds, and depending on their
nature saponins are classified in two main groups (Figure 2):
1.- Steroidal saponins, whose aglycone is steroidal, most
of which are present in monocolyledonous angiosperms.
The aglycone can be of the spirostanoid (Figure 2A) or
furostanoid types (Figure 2B).
2.- Triterpene saponins, whose aglycone is terpene
(Figure 2C), most of which are present in dicotyledonous
Saponins from the genus Asparagus belong to the group
of steroidal glycosides . In A. officinalis L., and most of the
green and white commercial hybrids, basically derived from
this specie, the main and almost only saponin is protodioscin
(C51H84O22), which is a glycoside derivative of diosgenin of
the furostanoid type [9,11]. Beside commercial hybrids, in
some markets, it is found the so-called “triguero” asparagus
which grows either wild or cultivated from species other
than A. officinalis. We found that “triguero” asparagus from
Huétor-Tájar, a place from Granada in Spain, has a distinct
saponin profile compared to commercial hybrids [10,12]. The
results revealed that, although commercial hybrids contain
protodioscin as the major saponin, “triguero” from Huétor-
Tájar presents a more complex profile. This consists on a
combination of protodioscin and at least 12 different new
saponins derived from a furostanol-type steroidal genin with
a single bond between C5 and C6 of the B ring. The same kind
of saponins have been found in different wild species while
only protodioscin was found in wild A.officinallis[10,12-13].
The chemical structure of all of these saponins was classified
by their retention time, molecular weight and fragmentation
pathway, and as well as the co-injection with authentic
reference saponins previously purified and identified from
Huétor- Tájar “triguero” [10,12]. The fragmentation pathway
has been studied through the mass spectra obtained in
negative (100V-) and positive (50V+) modes (Table 1).
Changes in the structure of saponins can cause
functional alterations. Mimaki and co-workers [14,15] have
systematically examined the cytotoxic activities of the
steroidal saponins mainly isolated from the Liliaceae plants,
against HL-60 human promyelocytic leukemia cells and found
several structures-activity relationships. Some steroidal
saponins evaluated in the assay system showed considerable
cytotoxic activities, which were almost as potent as that of
etoposide used as a positive control. The activities were found
to be sensitive to the monosaccharides constituting the sugar
moieties and their sequences, as well as to the structures of the
aglycones. In that study, they revealed that in the diosgenylα-
l-rhamnopyranosyl-(1 → 2)-β-d- glucopyranoside derivative,
which is cytotoxic, the diglycoside exists in a vertically oriented
conformation against the steroid plane.However,in the
derivative, which presents a conformation with the diglycoside
and the steroid in the same plane, the activity was not relevant.
According to our previous studies [10,12,13], the different
saponins identified from wild and cultivated asparagus spears
(Table 1), have different substituents in the sapogenin as well
as differences in the composition, linkage and number of sugar
chains. This significant structural variation suggests that they
might also have different bioactivities.
Saponins are present in more than 100 plant families
and in some marine sources . As previously, mentioned,
steroidal saponins are distributed in monocotyledonous plants
(Agavaceae, Dioscoreaceae, Liliaceae, Asparagaceae) and
triterpenes are mainly found in dicotyledons (Leguminosae,
Araliaceae, Caryophyllaceae). Most of the saponins present in
the diet are of the triterpene type; in fact, the main sources
are the legumes (soya, chickpeas, beans, beans, lentils, etc). In
addition to legumes, pumpkin, licorice, beetroot, spinach and
tea are also sources of triterpenic saponins. On the other hand,
steroidal saponins are found in some foods such as asparagus,
tomato, yucca, garlic or leek. In the case of cultivated white and
green asparagus (A. officinalis), it has been reported that the
main saponin they contain is protodioscin at concentrations
of 1.4 to 5mg/100g fresh weight  and 0.024 -2.5mg/100g
fresh weight , depending on the variety and the part of the
Although A. officinalis L. is the only cultivated asparagus
nowadays, other wild species are also edible and traditionally
consumed such as A. Pseudoscaber Grecescu, A. matitimus (L.)
Mill., A. brachiphyllus Turcz., A. prostratus Dumort and A. officinalis
L. . In addition, both in Spain and in other countries
of the Mediterranean area, three climbing plants of wild origin
have been traditionally consumed under the name of "asparagus"
(Bryonia dioica Jacq., Tamus communis L. and Humulus
lupulus L.), due to their great resemblance to asparagus in
terms of its phenotypic and organoleptic characteristics .
In the case of T. communis, its saponins are of the steroidal type
derived from diosgenin, as in the case of most asparagus. In
contrast, B. dioica and H. lupulus contain triterpene saponins.
As they occur in the other wild asparagus, the concentrations
of saponins in these three edible climbing plants are high 
and vary depending on the part of the plant that is ingested
It is important to mention that saponins can also be
administered as food additives in order to improve the stability
of the food itself or to give concrete effect at the functional level.
These additives come from other foods that contain saponins
naturally. Examples are Mohave yucca (Yucca schidigera Roezl
Fla) and quillaja (Quillajasaponaria Mol Fla), which have been
classified as food additives in the United States under section
172.50 (Natural Flavoring Substances and Natural Substances
Used in Conjuction with Flavors) .
Scientific studies on the absorption, metabolism and
pharmacokinetics of saponins have shown that saponins
are not practically absorbed after oral administration,
because they are mainly eliminated by faeces. It is known
that saponins have a low intestinal absorption mainly due
to unfavorable physicochemical characteristics. In the
understanding of absorption of saponins, it is important
to remark that sapogenins have shown improved chemical
properties compared to their precursor saponin, that enhance
their permeability, such as a lower molecular weight, higher
lipophilicity or lower molecular flexibility [21,22].
However, the aqueous solubility in the intestinal media
is worst for sapogenins due to the lack of a hydrophilic sugar
chain, which limits their bioaccessibility and therefore their
bioavailability [22,23]. Liu et al.  effectively showed
that the solubility of saponins significantly decreased for
compounds with fewer or no sugar moieties attached. As
example, glycyrrhetic acid, the sapogenin from glycyrrhizin of
licorice was found in plasma after oral digestion of this saponin,
whereas glycyrrhizin was barely detectable . Kamo et al.
 also described a higher bioavailability of soyasapogenols,
the sapogenin of soyasaponins from soya in rats, compared to
the bioavailability of soyasaponins. Additionally, these authors
also found that the bioavailability was different depending
on the type of saponin and sapogenin. Furthermore, due to
the great variability on the chemical structure of saponins
and sapogenins, the reported values of bioavailability are
diverse. Studies on the bioavailability of steroidal saponins,
such as those found in asparagus, have shown that saponins,
such as dioscin and protodioscin, have a very low absorption,
reaching values of bioavailability of 0.2%. However, they
were found to have a very high average life time (120hours)
[27,28]. Similarly, He et al.  observed that the absorption
of methylprotodioscin was greater than dioscin. These effects
are similar to those described for triterpene saponins .
Additionally, considering the reviews performed by Gao et al.
 about the bioavailability of popular saponins in different
animals, some of the observed values were as low as 0.1% for
saponins from ginseng (ginsenosides) in rats, or 3% in dogs,
and as high as 90% for the sapogenin from licorice (glycyrrhetic
acid), also in rats. Moreover, due to the poor small intestinal
absorption, saponins reach the colonic tract, suggesting that
the microbiota is the main responsible for their hydrolysis and
production of sapogenins.
It is important to remark that the events that take place
during digestion are highly related to the bioactivities of
saponins. This is because most studies have suggested that
saponins are poorly absorbed, therefore their residence time
within the gastrointestinal lumen causes important bioactive
events. Additionally, some studies have shown interesting
inhibitory activities of saponins of digestive enzymes such
as lipase, amylase or glucosidase enzymes, which are effects
related to their final bioactivities .
One of the main functions that have been attributed to
asparagus saponins for years is its hypolipidaemic effect
because diets rich in saponins have been shown to lower
cholesterol levels, improving the lipid profile [3,5]. Moreover,
it has been shown that the presence of steroidal saponins in
the asparagus is able to improve the lipid profile by decreasing
the levels of total cholesterol, LDL and triglycerides [2,33-34].
These authors justify the hypolipidaemic effect by decreasing
the absorption and synthesis of cholesterol.
Numerous studies have shown the cytotoxic and antitumor
properties of steroidal saponins present in asparagus edible
part [4,35-36]. We have shown  that steroidal saponins
from edible spears of “triguero” asparagus from Huétor-Tájar,
when in contact with human colon cancer HCT-116 cells block
ERK, AKT, and p70S6 (mTOR) signaling pathways, arrest the
cell cycle at G0/G1 phase by interfering the expression of
cyclins D, E, and A, and induce cell death through the apoptotic pathway via caspase-3, leading to PARP-1 cleavage and DNA
In addition, the cytotoxic capacity of saponins depends on
their structural characteristics. Indeed, some authors [16,37]
have shown that the structure of sugars in steroidal saponins
plays a very important role in the cytotoxicity against certain
tumors. Other studies have shown that the type of aglycone
also influences the cytotoxic effect [38-40].
Asparagus steroidal saponins have also antifungal
activity; however, it seems that only spirostanol derivatives
are active while furostanol derivatives are inactive .
The crude saponin fraction obtained from the bottom cut
of A. officinalis L . h as s pecific a ctivity t o c ertain f ungi s uch
as Candida, Cryptococcus, Trichophyton, Microsporum and
Epidermophyton. The mechanism of antifungal action of
saponins is not well understood but it is believed that they
complex with sterols in the cell membrane, leading to pore
formation and consequent loss of membrane integrity.
Asparagus saponins are characterized by their structure
containing a steroidal aglycone and one or more sugar units.
Consumer’s demand for natural products, coupled with their
physicochemical (surfactant) properties and biological activity
(anticancer and anticholesterol activities), has led to the
emergence of asparagus saponins as commercially significant
compounds with expanding applications in food, cosmetics,
and pharmaceutical sectors. The full realization of their
commercial potential requires development of commercially
feasible processes that can address processing challenges
posed by their complex nature, including their stability.
Information on the composition (qualitative and quantitative)
and properties of the saponins present in asparagus, and the
effects of processing on their composition and properties are
key elements for successful process design. The abundance of
saponins in asparagus spears and their presence in significant
quantities in their processing and cultivation by-products
result in a wide range of natural materials that can be exploited
for saponin commercial production.