Purslane: A Review of its Potential for Health and Agricultural Aspects

Abstract

Purslane (Portulaca oleracea L.) is a common weed that grows all over the world and is one of the most widespread weed species in summer crops. However, it has great potential to become a new crop since its identification as one of the best plant sources ofω-3 fatty acid, α-linolenic acid, as well as some antioxidants (α-tocopherol, β-carotene, ascorbic acid, and glutathione). Several other features distinguish this species: high content of crude protein, water-soluble polysaccharides useful as gums, and good tolerance to salinity. This review summarizes purslane’s origin, botanical, and physiological features while its nutritional and medical properties are reported in reference to several studies carried out on its chemical properties. Finally, its cultivation potential is discussed and future uses are proposed for this species, mainly as a component in ready-to-use vegetables (especially in mixed packaging) but also for other cultivation purposes.

Full text

Received: 11 February, 2009. Accepted: 2 March, 2010. Invited Mini-Review
The European Journal of Plant Science and Biotechnology ©2010 Global Science Books
Purslane: A Review of its Potential
for Health and Agricultural Aspects
Maria Gonnella1* • Monia Charfeddine2 • Giulia Conversa3 • Pietro Santamaria4
1 Istituto di Scienze delle Produzioni Alimentari, CNR, Via Amendola 122, 70126 Bari, Italy
2 C.R.A. - Istituto Sperimentale Agronomico, Via Celso Ulpiani 5, 70125 Bari, Italy
3 Dipartimento di Scienze Agro-Ambientali, Chimica e Difesa Vegetale, Università di Foggia, Via Napoli 25, 71100 Foggia, Italy
4 Dipartimento di Scienze delle Produzioni Vegetali, Università di Bari, Via Amendola 165/a, 70126 Bari, Italy
Corresponding author: * maria.g onnella@ispa.cnr.it
ABSTRACT
Purslane (Portulaca oleracea L.) is a common weed that grows all over the world and is one of the most widespread weed species in
summer crops. However, it has great potential to become a new crop since its identification as one of the best plant sources of -3 fatty
acid, -linolenic acid, as well as some antioxidants (-tocopherol, -carotene, ascorbic acid, and glutathione). Several other features
distinguish this species: high content of crude protein, water-soluble polysaccharides useful as gums, and good tolerance to salinity. This
review summarizes purslane’s origin, botanical, and physiological features while its nutritional and medical properties are reported in
reference to several studies carried out on its chemical properties. Finally, its cultivation potential is discussed and future uses are
proposed for this species, mainly as a component in ready-to-use vegetables (especially in mixed packaging) but also for other cultivation
purposes.
_____________________________________________________________________________________________________________
Keywords: -3 fatty acids, nitrate, oxalate
Abbreviations: ALA, -linolenic acid; DHA, docosahexanoic acid; EPA, eicosapentaenoic acid; FA , fatty acids; LA, linoleic acid; NO3
-,
nitrate; OA, oxalic acid
CONTENTS
INTRODUCTION...................................................................................................................................................................................... 131
HISTORICAL, AGRICULTURAL AND PHYSIOLOGICAL ASPECTS OF PURSLANE..................................................................... 131
NUTRITIONAL AND MEDICINAL CHARACTERISTICS AND USES................................................................................................ 132
OTHER USES............................................................................................................................................................................................ 134
CULTIVATION .......................................................................................................................................................................................... 134
REFERENCES........................................................................................................................................................................................... 135
_____________________________________________________________________________________________________________
INTRODUCTION
Purslane is a weed commonly found on all continents. It has
an enormous potential for infestation mainly due to the
large number of seeds produced per plant: up to 500 seeds
kg-1 of soil were found, but severe infestations depend
largely on the amount and frequency of rainfall in summer
(Unger et al. 1999). In addition, it has a particular ability to
re-root after cultivation or hoeing, because the fleshy stems
remain moist and viable for several days and have a great
potential to form roots (Cudney and Elmore 1999). It forms
a dense mat covering the soil and preventing the emergence
of other seedlings. Its aggressive and prostrate growth has
suggested that purslane can be used as a living mulch inter-
cropped with a row crop, for example broccoli, whose yield
was not reduced when compared to conventional methods
of weed control, such as black plastic mulch, mechanical or
chemical control (Ellis et al. 2000).
Purslane has received renewed interest since the identi-
fication of some of its nutritional and medicinal properties,
so much so that it has been described as a “power food of
the future” (Levey 1993) and been proposed as a “new
crop” (Kumamoto et al. 1990).
HISTORICAL, AGRICULTURAL AND
PHYSIOLOGICAL ASPECTS OF PURSLANE
The botanical name is Portulaca oleracea L., belonging to
the Portulacaceae family. Seven subspecies belong to this
species, but the subspecies oleracea and sativa are the most
common. P. grandiflora is also widespread as a flower spe-
cies. The Latin name seems to have two meanings: a) ‘little
door’, deriving from the latin ‘portula’, because of the way
its capsule opens, and b) ‘porto’ (which means carry) plus
‘lac’ (which means milk), referring to the succulent consis-
tence of stems and leaves (Simopoulos 1987). In the Middle
Ages the Arabs called it ‘baqla hamqa’, which means ‘mad’
or ‘crazy vegetable’, because its branches spread over the
ground without control. Purslane seems to have an Asian
origin (Iran, India, Russian southern regions) (Nuez and
Hernández Bermejo 1994). De Candolle (1884) supposed
that it was cultivated more than 4,000 years ago. In Ancient
Egypt it was already used as a medicinal plant. There is evi-
dence of its cultivation in Arabia and in the Mediterranean
Basin since the Middle Ages.
The species has a cosmopolitan distribution, but it is
more present in the Mediterranean area, mainly in the arid
and semi-arid lands of northern Africa and southern Europe.
In particular, in Saudi Arabia, the United Arab Emirates,
®

The European Journal of Plant Science and Biotechnology 4 (Special Issue 1), 131-136 ©2010 Global Science Books
and Yemen, P. oleracea subsp. sativa is largely cultivated
and available in many vegetable shops and used as salad. In
the USA purslane is considered a minor crop because of its
use in ethnic cooking (Cudney and Elmore 1999). Wild
purslane was sold by street-vendors in southern Italy during
the 1950s and 60s.
‘Purslane is a summer herbaceous plant, with branched,
decumbent or fairly ascending stems’ (Nuez and Hernández
Bermejo 1994). Cultivated forms are more upright and
vigorous than wild forms. Plants are succulent, glabrous,
with reddish cylindrical stems, up to 50 cm long, with dico-
tomic growth. Leaves are opposite, oval and glabrous, fleshy,
spoon-shaped, up to 3 cm long. Root is a taproot. Flowers
are yellow, small, with 5 petals, frequently solitary at the
end of the branches, where secondary stems grow. Flower-
ing occurs from July to September. Fruits are capsules con-
taining a lot of black seeds. The germinating capacity lasts
eight to ten years if the seeds are stored dry at a low tempe-
rature (Nuez and Hernández Bermejo 1994; Stephens 1994;
Mitich 1997). The weight of 1,000 seeds is about 0.13 g.
Purslane is well adapted to poor soils, requiring a mini-
mum of water during germination and emergence. Purslane
has been rated as moderately salt tolerant, with a threshold
value of 6.3 dS m-1; yield is halved when the electrical
conductivity of saturated-soil extract reaches 11.5 dS m-1
(Kumomoto et al. 1990). In another study the threshold of
salinity was similar (6.8 dS m-1) but there was a lesser
decrease in yield (in plants exposed to irrigation solutions
with EC value of 24.2 dS m-1, the yield reduction was
around 30% only) (Teixeira and Carvalho 2009). Due to its
salt tolerance, purslane has been proposed as a prospective
halophytic species for desalinating saline soils and for
drainage water reuse systems (Grieve and Suarez 1997).
The halophytic nature of purslane, when used as a compa-
nion plant, could be useful to increase the yield of the main
crop. This is due to purslane’s ability to take up large
amounts of Na+ and Cl- from the cultivation medium under
saline conditions. It was observed that Na+ concentration in
tomato leaves was reduced by 36% when grown with purs-
lane, while fruit yield increased by 33%. This is explained
by the fact that tomato plants are able to use more energy to
elaborate substances for fruit development, instead of buil-
ding up mechanisms of salt tolerance (Graifenberg et al.
2003). Purslane removed 210 kg/ha of Cl and 65 kg/ha of
Na when cultivated at 6.5 dS m-1 as an intercrop in fruit or-
chards during one growing season (Kiliç et al. 2008). Sear-
ching for the physiological and biochemical mechanisms at
the base of their salt tolerance, a recent study found that
purslane plants responded to NaCl stress through increased
antioxidant activities (catalase, ascorbate peroxidise, gluta-
thione reductase) and the accumulation of osmoprotectant
proline (Yazici et al. 2007).
Purslane is a C4 succulent plant that under drought
stress changes its metabolism to a Crassulacean acid like
metabolism (CAM), as evidenced by changes in its CO2
exchange pattern, malic acid content, titratable acidity, spe-
cific changes of leaf structure and activity of phosphoenol-
pyruvate carboxylase, responsible for the diurnal fixation of
CO2 in C4 plants and nocturnal in CAM plants (Lara et al.
2004).
NUTRITIONAL AND MEDICINAL
CHARACTERISTICS AND USES
Leaves and stems of purslane can be eaten cooked in soups
and several dishes. But the most frequent use of purslane is
raw in mixed salads, particularly appreciated for its suc-
culence and slightly sourish taste, which is similar to water-
cress or spinach.
In the Middle East, the plant is used as a febrifuge, anti-
scorbutic (for high content of vitamin C), antiseptic, anti-
spasmodic, diuretic, vermifuge, refrigerant, and as a thera-
peutic herb against skin inflammations and mouth ulcers
(Chan et al. 2000). Plant extracts are used as bactericidal in
bacillary dysentery; the whole plant is considered an aphro-
disiac. Analgesic and anti-inflammatory properties have
been demonstrated (Chan et al. 2000; Sanja et al. 2009),
while the examination of the anti-fungal activity of purslane
extracts has revealed specific and marked activity against
dermatophytic fungi of the genera Trichophyton (Oh et al.
2000). Purslane extracts have shown none or slight cyto-
toxic or mutagenic effects, and even a weak inhibition of
tested mutagenic agents (Yen et al. 2001). Purslane extracts
have been demonstrated to have a skeletal muscle relaxant
effect that was associated with their high potassium concen-
tration (Parry et al. 1993). Purslane leaves and stems have
shown a high content of potassium (46,000 and 68,600 mg
kg-1 dry weight, dw, respectively for leaves and stems) toge-
ther with magnesium (46,400 mg kg-1 dw, on average for
two plant portions) and calcium (60,000 and 25,400 mg kg-1
dw, respectively for leaves and stems), even if potassium
and calcium levels were reduced by high salinity exposure
(Teixeira and Carvalho 2009). The consideration of purs-
lane as antidiabetic in the Chinese folk medicine can be
supported by the fact that crude polysaccharide extracted
from purslane has been assessed to control blood glucose
and the metabolism of glucose and blood lipids in diabetes
mellitus mice. The dose of 400 mg kg-1 body weight was
the optimal level (Gong et al. 2009). Purslane polysaccha-
rides have also showed free radicals scavenging activities
and protective effects against oxidative damage of rats with
ovarian cancer (Chen et al. 2009).
Some studies indicate that consumption of purslane may
help to reduce the occurrence of cancer and heart disease
(Simopoulos 1991). This may explain the definition as a
‘vegetable for long life’ that purslane has in Chinese folk-
lore. These properties may be related to its high content of
catecholamines (noradrenaline and dopamine, 0.15 and
0.25%, respectively) (Zhang et al. 2002). In particular, nor-
adrenaline has been shown to be a modulator of the immune
system and have anti-cancer properties. The highest content
of catecholamines has been found in leaves (0.074 and
0.69% for noradrenaline and dopamine, respectively) com-
pared to stems (0.029 and 0.18%) and seeds (0.054 and
0.59%) (Chen et al. 2003). It has been reported that green
leaves of wild and cultivated plants of P. oleracea have a
very high content of phenols, such as epigallocatechin (111
and 76 g g-1 dw) and luteolin (43 and 10 g g-1 dw, respec-
tively for leaves of wild and cultivated plants), though
higher amounts of these compounds have been found in the
root extracts. Roots of wild and cultivated plants have shown
a higher Total Phenolic Content (486 and 311 mg GAE/100
g dw, respectively) than leaves (214 and 171 mg GAE/100
g dw, respectively), higher in wild plants than in cultivated
ones (Spina et al. 2008). In a DPPH assay estimating the
free radical scavenging activity, purslane has revealed an
IC50 of 54.33 g mL-1, much higher than that found for
other antioxidant agents used as control (Erclisi et al. 2008).
The same authors reported a very high value of equivalent
of phenolic compounds (17.88 g GAE mg-1 dw) in purs-
lane leaf extracts and high ascorbic acid content (77.25
mg/100 g fw) in fresh leaves. Another bioactive compound
found in purslane at levels remarkably higher than other
vegetables is melatonin, noted to have multiple functions as
free radical scavenging and antioxidant activity, synergic
activity with other compounds, like -3 fatty acids (Simo-
poulos et al. 2005). The main nutrient properties of purslane
are summerized in Tabl e 1 . It appears as an excellent source
of several bioactive constituents, including antioxidants (-
tocopherol, -carotene, ascorbic acid, and glutathione) and
-3 fatty acids (FA), among which -linolenic acid (ALA)
is particularly abundant. In 1986 it was first stated that
‘purslane is the richest source of omega-3 fatty acids of any
vegetables yet examined’ (Simopoulos and Salem, 1986).
Hence the Authors suggested that ‘purslane could be culti-
vated as a source of omega-3 fatty acids for human con-
sumption, fish feed or animal feed’. FAs are important lipid
components (Trautwein 2001). The -3 and -6 FAs are
defined as essential because mammals are not able to intro-
duce a double bond beyond position 6. Hence, they must be
132

Purslane, weed or crop? Gonnella et al.
provided by the diet. Linoleic acid (LA) and ALA are the
most important FAs in the -6 and -3 series, respectively.
The relationship between -3 and human health was de-
fined for the first time in the early 1970s when epidemiolo-
gical findings revealed that Greenland Eskimos had a lower
incidence of coronary heart diseases, despite a traditional
diet rich in fat and cholesterol, but rich also in long-chain
FAs coming from fish products (Bang et al. 1971). Since
then the ability of -3 to reduce the incidence of cardio-
vascular diseases, together with the anticancer and anti-
inflammatory functions, has been well documented through
many epidemiological studies (Simopoulos 1999; Ruxton et
al. 2004). Nevertheless, these functions are especially asso-
ciated to the long-chain -3 FAs, eicosapentaenoic acid
(EPA, C20:5) and docosahexanoic acid (DHA, C22:6), but
unfortunately, there is no known terrestrial plant source of
these compounds except for mosses. Fatty fish (tuna, sar-
dine, salmon, mackerel) provide a great amount of EPA and
DHA (Trautwein 2001). In addition to oil-rich fish, meat
and eggs can also make a contribution to the dietary intake
with long-chain -3 FAs (Givens and Gibbs 2005). The
long-chain -3 FAs EPA and DHA are also synthesized in
the human body from ALA provided by plants in the diet
(Burdge and Calder 2005). ALA is found in the chloroplasts
of green leafy vegetables (such as spinach, kale, cress, con-
taining 89, 350, 290 mg 100 g-1 fw, respectively) but it is
more abundant in seeds such as linseed, rapeseed and soy-
bean, as well as in their oils (54.2 and 7.7 g 100 g-1 in lin-
seed and soybean oil, respectively), and nuts (6.8 g 100 g-1
fw in walnuts) (Simopoulos 1991; Trautwein 2001). The
problem is that in most plants LA is present in greater
amounts and competes with ALA for their conversion to
longer chain FAs, by sharing the same metabolic pathway
and hence competing for the same enzymes (Trautwein
2001). In purslane, not only is ALA present in high amounts,
but it also prevails over LA (Simopoulos et al. 1992; Fon-
tana et al. 2006; Ercisli et al. 2008; Oliveira et al. 2009)
(Tab l e 2).
Purslane is widely consumed in Mediterranean coun-
tries such as Greece, where the incidence of cardiovascular
diseases and cancer is very low (Simopoulos 2001). The
ALA content in purslane leaves is several times higher than
in spinach, mustard, and lettuce (Simopoulos et al. 1992;
Simopoulos 2001). One hundred grams of fresh purslane
leaves can provide 300-400 mg of ALA, 12.2 mg of -toco-
pherol, 26.6 mg of ascorbic acid, 14.8 mg of glutathione
and 1.9 mg of -carotene (Simopoulos et al. 1992). In wild
and cultivated Australian varieties, a level of FAs was found
in leaves ranging from 1.5 to 2.5 g kg-1 fresh mass (fm)
where ALA accounted for 60% (Liu et al. 2000). In stems
the total FA content was lower (Omara-Alwala et al. 1991);
but it was higher in seeds, from 80 to 170 g kg-1 fm, with
30-40% accounted for by ALA (Liu et al. 2000). The dif-
ference in ALA concentrations reported by various authors
in leaves (Tab l e 1) may be due to differences in cultivars,
sample material, sampling procedure, time of growth and
analytical methods. When considering a mean ALA concen-
tration in leaves of 1,000 mg kg-1 fm, it may be estimated
that a 100 g portion of purslane might supply around 10%
of average intake of approximately 1 g/day of ALA. This
fraction appears limited if compared with the amount of
EPA and DHA directly provided by other foods, especially
oil-rich fish, but some considerations are useful. A low
percentage of the population eat fish, for example only 27%
of the UK population (Givens and Gibbs 2005). In general
the -3 FA intake is limited by patterns of food choice and
by the low availability of fish stocks to sustain the supply of
both oil-rich fish and fish oil for human diet (Burdge and
Calder 2005). Moreover, the continued and increasing use
of fish oils in animals’ diet to enrich meat, eggs, and milk in
-3 FAs is not sustainable, taking into account that the
efficiency of incorporation of -3 FAs into edible tissues or
products is low (Givens and Gibbs 2005). In this respect,
any alternative and sustainable source of fatty acids should
be considered. In a specific study purslane was able to in-
crease the polyunsaturated FAs and to reduce the saturated
FAs content in egg yolk, when dried purslane was sup-
plemented to hens diet by 20% (Dalle Zotte et al. 2005).
Studying the influence of planting date on different
purslane accessions from Greece, Egypt, and the USA,
purslane was confirmed as the most abundant terrestrial
vegetable source of essential -3 FAs, regardless of its
genetic diversity, while the total lipid content was higher in
the first planting date (Ezekwe et al. 1999). Plants not dif-
fering in total FA content were obtained at the 14-true-leaf
stage compared with the 6-true-leaf stage, but with a higher
-3/-6 ratio and lower levels of saturated FAs at the 14-
true-leaf stage (Palaniswamy et al. 2001). On the other hand,
fatty acid concentration in chamber-grown purslane plants,
harvested at different stages of growth, showed the highest
ALA content in leaves at 30 days after planting, compared
with 49 and 59 days (Omara-Alwala et al. 1991).
Since ALA is a critical constituent in chloroplasts (rep-
resenting two thirds of the total FAs in photosynthetic
tissues), it is assumed that nitrogen nutrition can affect its
Tab l e 1 Nutritional characteristics of purslane (values per kg of fresh
mass).
Compound Content References
Water (g) 940a USDA 2007
Protein (g) 13a USDA 2007
Total lipid (g) 1a USDA 2007
Ash (g) 12.5a USDA 2007
Carbohydrate (g) 34.3a USDA 2007
Calcium (mg) 650a USDA 2007
Iron (mg) 19.9a USDA 2007
Magnesium (mg) 680a USDA 2007
Phosphorus (mg) 440a USDA 2007
Potassium (mg) 4,940a USDA 2007
Sodium (mg) 450a USDA 2007
Vitamin C (mg) 210a USDA 2007
266b Simopoulos et al. 1992
840b Guil et al. 1997
Vitamin A (μg) 660a USDA 2007
Folate, total (μg) 120a USDA 2007
-tocopherol (mg) 122b Simopoulos et al. 1992
-carotene (mg) 21-30b Liu et al. 2000
19b Simopoulos et al. 1992
3.6-6.5c Liu et al. 2000
Glutathione (mg) 148b Simopoulos et al. 1992
Total fatty acids (mg) 856a Cros et al. 2007
1,620-2,560b Liu et al. 2000
590-870c Liu et al. 2000
81,800-177,000d Li u et al. 2000
-linolenic acid (mg) 481a Cros et al. 2007
970-1,600b Liu et al. 2000
3,000-4,000b Simopoulos et al. 1992
100-290b Omara-Alwara et al. 1991
700-1,330b Palaniswami et al. 2001
70-210c Liu et al. 2000
35,300-68,800d Liu et al. 2000
a: Whole plant; b: Leaves; c: Stems ; d: Seeds
Tab l e 2 Lipidic content and main fatty acid percentage contents in edible
portions of purslane (only values higher than 1% are reported) (adapted
from Guil et al. 1996).
Fatty acids Composition (%)
Lipids (g kg-1 fm) 3.9
-linolenic acid - 18:33 32.60
Palmitoleic acid - 16:17 20.96
Palmitic acid - 16:0 17.40
Linoleic acid - 18:26 16.82
Oleic acid - 18:19 5.89
Stearic acid - 18:0 3.46
Behenic acid - 22:0 3.33
Saturated acids/3 0.80
3/6 2.00
133

The European Journal of Plant Science and Biotechnology 4 (Special Issue 1), 131-136 ©2010 Global Science Books
content. In fact, the synthesis of ALA increases when chlo-
rophyll increases (Tremolieres et al. 1979), and chlorophyll
synthesis can in turn be influenced by nitrogen level and
form (Blanke et al. 1996; Osorio et al. 2003). In some spe-
cies total FA synthesis is increased by supplying more nitro-
gen, while ammoniacal nitrogen causes an increase in chlo-
rophyll (Raab and Terry 1994; Flores et al. 2001). In purs-
lane, nitrogen form has a pronounced effect on the concen-
tration of FAs but does not affect FA composition and
modestly increases chlorophyll and thylakoid protein con-
tent. Probably the effect on chlorophyll content results from
an increased chloroplast volume, while total FA accumula-
tion is associated with FA storage in osmophilic lipid
globules in purslane chloroplasts (Palaniswamy et al. 2000).
A moderate salinity exposure (6.8-12.8 dS m-1) induced
a singular increase in total lipid content (up to 20% on a dw
basis), but a detailed fatty acid profile of lipid fraction was
not reported in this paper (Teixeira and Carvalho 2009). In
another paper, the applied saline treatments (from 0 to 120
mM NaCl) did not significantly changed the total amount of
fatty acids (which slightly increased until 40 mM NaCl),
while the ratio 6 to 3 remained unchanged, approxi-
mately at 0.3 (Carvalho et al. 2009).
Despite the nutritive value of purslane, its introduction
and acceptance into the human diet is limited by large con-
tents of oxalic acid [OA, (COO-)2], which is formed in
plants as a metabolism end product. After intake, it can
cause the formation of kidney stones and disorders mainly
due to reduced bio-availability of cations (Ca2+, Mg2+, Fe2+,
K+). Noonan and Savage (1999) placed purslane in the
Group 1 of species containing the highest levels of oxalate,
ranging from 9.1 to 16.8 g kg-1 fm, often higher than spi-
nach (3.2-12.6 g kg-1 fm). Recently, oxalate levels for raw
purslane leaves have been found much higher than the pre-
viously reported range (23.4 g kg-1 fm of total oxalate)
(Poeydomenge and Savage 2007). OA concentration can be
reduced in plants grown in soilless systems. In hydroponics,
the highest OA content (6.2 g kg-1 fm) was found in leaves
at the 8 true-leaf stage (Palaniswamy et al. 2004), whereas
in floating systems the highest value was 5.0 g kg-1 fm
(Charfeddine 2004). OA accumulation in vegetables can be
limited by ammoniacal N nutrition (Elia et al. 1998). In-
creasing NH4
+ in the nutrient solution from 0% to 75% of
total N, the OA content in leaves decreased (from 6.2 to 3.8
g kg-1 fm) (Palaniswamy et al. 2004). Similar result was
found by Fontana et al. (2006). Explanation is that am-
monium assimilation avoids the synthesis of organic acids,
such as OA, that, on the contrary, are synthesized during
nitrate assimilation to neutralize OH- ions. It has also been
proposed that nitrate ions inhibit the OA oxidase activity,
resulting in the accumulation of OA in leaves and stems
(Libert and Franceschi 1987). A combination of NH4
+ 65%
in the nutrient solution with harvest at the 16-true leaf stage
would optimise the nutritional value of leaves (lower OA
and higher -3 FA concentrations) (Palaniswamy et al.
2004). A sharp decrease in total oxalic acid content was
found at increasing salt concentration in the hydroponic
nutrient solution after 30 days of saline stress (Carvalho et
al. 2009). Leaves harvested from plants grown in shaded
light contained more total and insoluble oxalates than those
grown in full light, while the soluble oxalate contents were
similar (Moreau and Savage 2009). The addition of yoghurt
to raw purslane leaves (as it is often consumed in some
countries, like Turkey) reduced the total oxalate content, but
in particular the soluble oxalate from 53.0 to 10.7% of the
total oxalate content. Maybe the soluble oxalate is conver-
ted in insoluble oxalate by calcium coming from milk
products (Moreau and Savage 2009). Brief cooking (5 min)
in boiling water did not changed the content of soluble or
insoluble oxalate (Moreau and Savage 2009), in contrast to
the earlier study by Poeydomenge and Savage (2007) who
found a reduction up to 33.5% of soluble oxalate in the
leaves and 18% in the stems by boiling purslane for the
same time. A greater loss (66.7%) of soluble oxalate was
caused by pickling in vinegar (Poeydomenge and Savage
2007).
Purslane is classified as a species rich in nitrate (NO3
-
>2,500 mg kg-1 fresh matter, fm) (Corré and Breimer 1979).
However, NO3-N fed purslane shoots harvested in July
showed a NO3
- content around 1,000 mg kg-1 fm, that was
greatly reduced by supplying ammoniacal nitrogen alone or
with nitrate (Charfeddine 2004). Much higher values (3,200
mg kg-1 fm) were found in purslane leaves picked from wild
plants in Spain (Guil et al. 1997). Wild plants picked in sou-
thern Italy showed an average nitrate content of 520 mg kg-1
fm (Bianco et al. 1998), ranging from 360 to 2,100 mg kg-1
fm in a further survey (Bianco 2002).
OTHER USES
A protein level of up to 22-25%, comparable to other forage
or vegetable food crops traditionally used as protein sources,
also suggests an alternative use of purslane for both animal
and human consumption (Ezekwe et al. 1999). However,
symptoms such as weakness, diarrhoea, colic and hepato-
nephropathy (probably due to the high content of free oxa-
late or the presence of anthraquinone and coumarin) may be
associated with daily and abundant doses of purslane as
fodder (Obied et al. 2003). These symptoms have not been
reported for the Sudanese people who consume purslane as
a common vegetable dish (Obied et al. 2003).
Purslane has been proposed as an effective ‘biomoni-
toring tool’ of fresh water environments and as an alumi-
nium toxicity testing plant. Aluminium toxicity symptoms
are concentration dependent and expressed through the
inhibition of root growth and increased decay of leaves and
stems. The aluminium toxicity in purslane can be fixed next
to Cu (Cd > Cu > Al > Zn > Hg > Se > Pb) (Anandi et al.
2002). At sites contaminated with multiple metals of indus-
trial origin where purslane naturally grows, it produces high
biomass thanks to its high regeneration power, fast growth
and short life cycle, showing also a good potentiality to
hyperaccumulate Cd, Cr and As, especially in roots. Hence
purslane may be successful employed for phytoremediation
aims (Tiwari et al. 2008).
Purslane leaves are a good new source of gum useful as
a food emulsifier (Garti et al. 1999).
CULTIVATION
Cultivation does not present technical difficulties. In experi-
ments carried out on the south-eastern coast of Spain, uni-
form production of 6-8 cm seedlings was obtainable after a
month during winter and spring in an unheated polyethy-
lene greenhouse (Nuez and Hernández Bermejo 1994). In
southern Italy it was grown in floating system in unheated
greenhouse giving a total yield of tender shoots from 9 to
15 kg m-2 in several mowings during three months (Tab l e
3). In soil it yielded about 16 kg m-2 after four months
(Tab l e 3).
The species seems very suitable for floating system cul-
tivation. It provides a completely edible product, charac-
terized by high juiciness and optimal nutritional properties.
The cultivation cycle can be protracted ad libitum, through
successive mowings, allowed by purslane’s high capacity
for budding again and by the late growth of seedlings after
mowing (Charfeddine 2004). In two greenhouse experiments,
purslane produced up to 15.1 and 9.2 kg m-2 of shoots, 6-8
cm long, with a dry matter content of 60 g kg-1 fm (Ta b l e 3 ).
The cultivation cycle lasted almost 3 months, from sowing
to the last harvest. Both trials were closed in the first decade
of July, but plants could still produce shoots, in spite of high
air temperature and high salinity in the nutrient solution.
Water consumption was quite high (220 and 275 l m-2, res-
pectively in the two cycles), due to high evaporation from
substrate when polystyrene boards were left bare after shoot
mowing (Charfeddine 2004). In three experiments carried
out in floating system comparing different substrates, Cros
et al. (2007) obtained higher yields of young shoots with
five leaf pairs when grown on peat alone (1.8 kg m-2 and 2.2
134

Purslane, weed or crop? Gonnella et al.
kg m-2, respectively, in the first two experiments and in the
third) or with perlite (3 peat: 1 perlite mixture) (1.8 kg m-2)
and on vermiculite only in two of the three experiments (1.9
kg m-2). These yields were obtained in a brief time, between
13 and 18 days after sowing (Cros et al. 2007). The same
authors rejected purslane soil growing due to the rapid for-
mation of mucilage in leaves and stems and the difficulty of
harvesting (Cros et al. 2007). In other experiments purslane,
grown in floating system on peat, yielded at maximum 1.8
kg m-2 of leaves plus 1.2 kg m-2 of stems with N supplied
with a 40/60 NO3
-/NH4
+ ratio (Fontana et al. 2005).
This technique allows the grower to obtain shoots free
of cultural residues (soil or substrate particles) that, appro-
priately packaged (e.g. in trays closed by plastic film),
might be introduced in ready-to-use vegetable production.
Under these conditions, it keeps well at low temperatures
for up to two weeks. Tender shoots have a milder flavour
and texture which make them more appetizing compared to
the whole plant (Nuez and Hernández Bermejo 1994). Fur-
ther investigations are needed to verify both the agronomic
profitability and the maintenance of the nutritional proper-
ties in relation to the cultivation system and storage of this
potentially valuable healthy food source.
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