ArticlePDF Available

Fatty acid composition and rheological behaviour of prickly pear seed oils

  • olive tree institute

Abstract and Figures

Prickly pear fruits constituted valuable foodstuff for humans and animals in arid and semi-arid regions. Two species of prickly pear from Tunisia, Opuntia ficus indica and Opuntia stricta, were investigated for fatty acid composition and physicochemical parameters of the seed oil. No significant difference in either physical or chemical parameters was found between the species. The main fatty acids of prickly pear seed oil were C16:0, C18:0, C18:1, C18:2. With an exceptional level of linoleic acid, up to 70%, the content of unsaturated fatty acids was high, at 88.5% and 88.0% for O. ficus indica and O. stricta, respectively.Rheological properties were analysed with changes of temperature and shear stress. Variations of viscosity were measured and the viscoelastic parameters were determined during heating and cooling cycles between 20 and 70 °C. Curves of flow were established with up and down cycles of shear stress at different temperatures. These measures highlighted the presence of large aggregates of crystal fatty acids in both Opuntia crude oils. Shearing and temperature destroyed this structural state and gave birth to an homogeneous stable suspension.The structural state of crude oil was confirmed using a contrast phase microscope, and the particle size distribution was obtained by laser granulometry.
Content may be subject to copyright.
Fatty acid composition and rheological behaviour
of prickly pear seed oils
Monia Ennouri
, Bourret Evelyne
, Mondolot Laurence
, Attia Hamadi
´dÕAnalyses Alimentaires, Ecole Nationale dÕInge
´nieurs, BPW 3038 Sfax, Tunisie
Laboratoire de Physique Mole
´culaire et Structurale, Faculte
´de Pharmacie de Montpellier, BP 14491, 34093 Montpellier Cedex 5, France
Laboratoire de Botanique, Phytochimie et Mycologie, UMR 5175, Faculte
´de Pharmacie de Montpellier, BP 14491, 34093 Montpellier
Cedex 5, France
Received 22 December 2003; received in revised form 13 October 2004; accepted 13 October 2004
Prickly pear fruits constituted valuable foodstuff for humans and animals in arid and semi-arid regions. Two species of prickly
pear from Tunisia, Opuntia ficus indica and Opuntia stricta, were investigated for fatty acid composition and physicochemical
parameters of the seed oil. No significant difference in either physical or chemical parameters was found between the species.
The main fatty acids of prickly pear seed oil were C16:0, C18:0, C18:1, C18:2. With an exceptional level of linoleic acid, up to
70%, the content of unsaturated fatty acids was high, at 88.5% and 88.0% for O. ficus indica and O. stricta, respectively.
Rheological properties were analysed with changes of temperature and shear stress. Variations of viscosity were measured and
the viscoelastic parameters were determined during heating and cooling cycles between 20 and 70 C. Curves of flow were established
with up and down cycles of shear stress at different temperatures. These measures highlighted the presence of large aggregates of
crystal fatty acids in both Opuntia crude oils. Shearing and temperature destroyed this structural state and gave birth to an homo-
geneous stable suspension.
The structural state of crude oil was confirmed using a contrast phase microscope, and the particle size distribution was obtained
by laser granulometry.
2004 Elsevier Ltd. All rights reserved.
Keywords: Prickly pear; Fatty acid; Seed oil; Rheology; Microscopy; Opuntia
1. Introduction
About 1500 species of cactus belong to the genus
Opuntia and are distributed mainly in Africa, Mediterra-
nean countries, southwestern United States, northern
Mexico and other areas (Hegwood, 1990). The main
studies on the Opuntia fruits were the chemical analysis
of pulp, skin and seeds (El Kossori, Villaume, El Bou-
stani, Sauvaire, & Mejean, 1998), analysis of volatile
constituents of pulp (Di Cesare & Nani, 1992; Flath &
Takahashi, 1978), use of pulp in juice production
(Espinosa, Borrocal, Jara, Zorilla, & Medina, 1973),
production of alcoholic beverage (Bustos, 1981), jam
production (Sawaya, Khatchadorian, Safi, & Al-
Mohammad, 1983) and the production of cocoa butter
equivalents from prickly pear juice fermentation by an
unsaturated fatty acid auxotroph (Hassan, Blanc,
Pareilleux, & Goma, 1995). An overview of processing
technologies concerning the fruits and cladodes of cac-
tus pear has recently been published by Saenz (2000).
Other authors have studied the nutritional significance
of Opuntia sp. (Stintzing, Schieber, & Carle, 2001).
0308-8146/$ - see front matter 2004 Elsevier Ltd. All rights reserved.
Corresponding author. Tel.: +216 98 278 684; fax: +216 74 221
E-mail address: (M. Ennouri).
Food Chemistry 93 (2005) 431–437
Crude young ÔnopalÕhave been studied as a source of
fibres (Majdoub et al., 2001), proteins and amino acids
(Teles, Whiting, Price, & Borges, 1997), and processed
in Taifi prickly pear sheets (Ewaidah & Hassan, 1992).
The extraction and the characterization of the prickly
pear mucilage from sheets was optimized by several
authors (McGarvie & Parolis, 1979;Medina-Torres,
Brito-De La Fuente, Torrestiana-Sanchez, & Katthain,
2000; Trachtenberg & Mayer, 1981, 1982).
Prickly pear seeds were first characterized by Sa-
waya, Khalil, & Al-Mohammad (1983), who demon-
strated that the seeds of Opuntia ficus indica are rich
in minerals and sulphur amino acids. A reserve protein
from the seeds has been isolated and characterized by
Uchoa, Souza, Zarate, Gomez-Filho, & Campos
(1998). The prickly pear seed oil composition and its
chemical characteristics were investigated by Sawaya
& Khan (1982), and then by Salvo, Galati, Lo Curto,
& Tripodo (2002).
Coskuner & Tekin (2003) studied the seed composi-
tion of prickly pear fruits during the maturation
period. Ramadan & Morsel (2003) compared the seed
and pulp oil compositions. However, the physical char-
acteristics of prickly pear oil are up to now unknown.
The major objective of the present work was to study
the physicochemical properties of the seed oil of the
O. ficus indica and O. stricta fruits which are the most
abundant species in Tunisia. Rheological behaviour
and microscopic structure have been studied and spe-
cial attention was paid to the effect of temperature,
since every food technological operation requires a
thermal treatment.
2. Materials and methods
2.1. Prickly pear seed
Mature Prickly pear fruits, O. ficus indica and
O. stricta, were collected, respectively, in August and
February from the same area (Sfax, Tunisia). The fruits
were immediately sorted, washed with running water,
air-dried and hand-peeled. A pulper finisher was used
to separate the seeds from the pulp. The seeds were
washed with distilled water several times, air-dried at
ambient temperature and then ground with a Diez
2.2. Oil extraction
The seed powders oils of O. ficus indica and O. stricta
were extracted with hexane in a Soxhlet extractor for
9 h. The organic phase was then removed using a rotary
evaporator under reduced pressure; the oil was flushed
with a stream of nitrogen and stored at 20 C in sealed
tubes prior to analyses.
2.3. Physicochemical analyses
The seed weight was appraized, at random, on one
hundred seeds. Moisture content was determined by
the AOAC method (AOAC, 1984). The oil yield was
determined on a seed powder of 5 g. Nitrogen was
determined by the Kjeldahl procedure and crude pro-
tein was calculated as N·6.25 (Balogun & Fetuga,
1986). The ash content was determined according to
the AOAC method (AOAC, 1990). Refractive index
was determined at 20 C with an Abbe refractometer
with temperature adjustment. The density was mea-
sured with a densimeter PAAR DMA 60. Saponifica-
tion number and iodine value were determined using
the official method (American Oil ChemistsÕSociety,
AOCS, 1993).
2.4. Fatty acid analysis
The fatty acid compositions of both oil samples were
analyzed by GC–MS after transesterification. Fatty acid
methyl esters were prepared in the presence of 2 N
potassium hydroxide in methanol and analyzed on a
Hewlett-Packard model 5890 series II gas chromato-
graph equipped with a flame ionization detector and a
polar capillary column: HP Innowax cross-linked
PEG, Carbowax 20 M (0.32 mm internal diameter,
30 m length and 0.25 lm film thickness). The opera-
tional conditions were: injector temperature 220 C;
detector temperature 275 C; column temperature 50
C for 5 min then a gradient of 10 C/min to 240 C; car-
rier gas was nitrogen at a flow of 1.47 ml/min. Three
injections were done.
2.5. Rheological measurements
2.5.1. Instrument
The rheological properties were measured using a
controlled stress Haake rheometer (Rheostress RS
100). All the rheological studies were conducted using
cone-plate geometry: 35 mm diameter and 2cone.
The volume of the sample was 0.4 ml. That equipment
is able to control temperature on a plate sensor system
to within ±0.1 C.
For the measures at variable temperature, the varia-
tion was at the rate of 5 C/min.
2.5.2. Flow curves
In order to determine the influence of temperature
and the shear rate, measures of viscosity were conducted
at constant shear stress (10 Pa) across increasing temper-
atures from 20 to 70 C and immediately decreasing
temperature to 20 C.
To follow the influence of shear rate on the viscosity,
increasing and immediately decreasing cycles of shear
stress at constant temperature were performed.
432 M. Ennouri et al. / Food Chemistry 93 (2005) 431–437
2.5.3. Dynamic tests
The rheological measurements, in oscillatory mode,
were performed in the linear viscoelasticity range (1
Hz in frequency and 0.3 Pa in shear stress) with temper-
ature increased from 20 to 70 C and followed immedi-
ately by a decrease of temperature to 20 C.
2.6. Microscopy
The oils of O. ficus indica and O. stricta were ob-
served under a contrast phase microscope equipped with
a Nikon F301 camera. A scale graduation, introduced
on photo, indicated the magnification.
2.7. Particle size distribution
The particle size distribution of crude oil was estab-
lished by laser light scattering at room temperature,
using a Malvern Mastersizer hydro 2000S (Malvern
Instruments Ltd, Malvern, UK). All analyses were per-
formed in triplicate.
3. Results and discussion
3.1. General composition (Table 1)
The oil contents for O. ficus indica and O. stricta,
were similar (10.90% and 11.05%, respectively). These
values were higher than the crude oil yield in the work
of Coskuner & Tekin (2003) (6.91%). The difference ob-
served is probably due to the origin of the fruit. Seeds
contain 5.4–3.9% protein and 1.1–1.64% ash, less than
values found by Sawaya et al. (1983) on the saudian
variety of O. ficus indica.
The value of viscosity at 20 CofO. ficus indica
(53 ·10
Pa s) is close to the value reported by Oomah,
Ladet, Godfrey, Liang, & Girard (2000) for grape seed
oil (49.4 ·10
Pa s), whereas the value for O. stricta
(76 ·10
Pa s) is comparable to that of rapeseed oil
(72–82 ·10
Pa s) (Karlesind & Wolff, 1992).
The refractive and iodine indices are comparable with
those of rapeseed oil (Karlesind & Wolff, 1992) (respec-
tively, 1.473 vs. 1.475 and 100 vs. 101.5). The saponifica-
tion value is lower than grape seed oil (188–194) but
compared favourably with native rapeseed oil (170–
175) (Karlesind & Wolff, 1992).
The density of the seed oil at 20 C compared favour-
ably with native rapeseed oil and soybean oil (0.910 and
0.921, respectively) (Noureddini, Teoh, & Davis Cle-
ments, 1992).
The study of the density of the Opuntia seed oil as a
function of temperature revealed a linear relationship
in accordance with results reported for others oils. It is
reported that the densities of fatty acids and triglycer-
ides are linear with temperature, according to the equa-
tion q=b+mT (Fisher, 1995). The linear coefficients b
and mfor the Opuntia seed oil are shown in Table 2. The
square correlation coefficient highlighted a linear corre-
lation between density and temperature.
For triglycerides, the change in density per degree
Celsius was in the range of 0.00067–0.00073 (Formo,
Jungermann, Norris, & Sontag, 1979). The results on
Opuntia oils were in accordance with these previous data
and with the published density data for coconut, corn
and rapeseed oils (Noureddini et al., 1992;Valeri &
Meirelles, 1997).
3.2. Fatty acid composition of prickly pear seed oil
The FAME compositions of seed lipids are listed in
Table 3. Linoleic acid is the major component (74%),
followed by oleic (12.8%) and palmitic acids (7.2%).
Both lauric and myristic acids were detected in O. srticta
oil in low amounts. Prickly pear seed oil was found to be
highly unsaturated: 88.5% and 88.0% for O. ficus indica
and O. srticta,, respectively. Besides the linoleic acid
(>70%), there is oleic acid (>12%). These results are in
agreement with those of Sawaya & Khan (1982) who
previously reported the contents of the four most impor-
tant fatty acids. The lipid pattern of prickly pear is com-
parable with that of sunflower and grapeseed oils (Tan
& Che Man, 2000).
Table 1
Physicochemical characteristics of the two species of Opuntia seed oil
O. ficus indica O. stricta
Weight of 100 seeds (g) 1.38 ± 0.08 1.69 ± 0.04
Dry matter (%) 93.00 ± 0.45 95.00 ± 0.30
Oil (%) 10.90 ± 0.10 11.05 ± 0.09
Protein (%) 5.40 ± 0.40 3.90 ± 0.20
Ash (%) 1.10 ± 0.10 1.64 ± 0.15
(Pa s) 0.0531 ± 0.0005 0.076 ± 0.001
Refractive index
1.475 ± 0.002 1.469 ± 0.001
0.903 ± 0.002 0.919 ± 0.001
Saponification number 169.0 ± 0.1 174.0 ± 0.3
Iodine value 101.5 ± 1.0 91.6 ± 0.5
Means of three determinations.
At 20 C and s> 2 Pa.
At 20 C.
Table 2
Linear correlation
between densities and temperature
for the two
varieties of Opuntia seed oil
Compound Intercept bSlope mR
O. ficus indica oil 0.91703 6.833E04 0.99
O. stricta oil 0.9336 6.9121E04 0.99
Density = b+mT.
Temperature range: 10–70 C.
M. Ennouri et al. / Food Chemistry 93 (2005) 431–437 433
Recently, Coskuner & Tekin (2003) reported a pal-
mitic acid content higher than our results (12% vs.
9.32%) and a content of linoleic acid very much lower
(52% vs. 70.29%). The observed difference is possibly
due to the degree of maturity of the fruit; indeed, these
authors suggested that there was an increase in saturated
fatty acid content towards the end of fruit maturation.
3.3. Rheological behaviour
3.3.1. Viscosity variations with the temperature
These measurement were carried out at constant
shear stress 10 Pa and two consecutive cycles of increas-
ing and decreasing temperature between 20 and 70 C.
As expected, the viscosity decreases strongly when the
temperature increases. The curve of viscosity was higher
on the curve segment corresponding to the decreasing
temperature of 70–20 C(Fig. 1). A weak hysteresis
was observed. When a second cycle of temperature
was applied, the viscosity curve was totally superposed
on the curve obtained in the phase 70–20 C of the first
temperature cycle (data not shown). At that time, the
structural state was stabilized.
The area of hysteresis observed was due not only to
the effect of the temperature but also to the effect of
the shearing. That result might be related to the chemi-
cal composition of the oil that revealed a significant
amount of fatty acids in the solid state at 20 C. Indeed,
palmitic acid and stearic acid have melting points of 62.9
and 69.6 C, respectively. The initial crude oil was a sus-
pension. During the first cooling, both shearing and
temperature destroyed the structural state, especially
the aggregates. Because this phenomenon was not
immediately reversible, hysteresis became visible when
temperature decreased to 20 C. The smaller size of par-
ticles explained the greater strength of resistance to flow
in the resulting suspension than in the initial suspension.
So the curve of viscosity during cooling was above the
curve of viscosity during heating. At that time, the sec-
ond cycle temperature, up 70 C and down to 20 C,
showed that there was no influence of shearing. A
homogeneous suspension took shape during the cooling
phase of the first temperature cycle.
3.3.2. Viscosity curves at different temperatures
This experiment aimed to explore variations of the vis-
cosity at constant temperature with increasing and imme-
diately decreasing shear stress. When the shear stress
increases, the viscosity increases from 11% to 24% for
all temperatures, 0.3 Pa. A weak decrease of viscosity
followed this rise and a stabilization was then observed
from 2 Pa. So the flow of oil became Newtonian when
the shear stress was above 2 Pa (Fig. 2). When the shear
stress immediately decreased, the behaviour remained
Newtonian in the same zone of shearing. This behaviour
was reproduced at every temperature but a weakening
of phenomenon was observed at 50 C and a near disap-
pearance at 60 C. These temperatures were in the same
range as the melting points of palmitic (62.9 C) and stea-
ric (69.6 C) acids. This flow characterized the physical
Table 3
Fatty acid composition of prickly pear seed oil (g/100 g of total fatty
Fatty acid Species
O. ficus indica O. stricta
Lauric C12:0
0.19 ± 0.01
Myristic C14:0
0.32 ± 0.01
Palmitic C16:0 9.32 ± 0.19 7.21 ± 0.09
Palmitoleic C16:1 1.42 ± 0.01 0.38 ± 0.02
Stearic C18:0 3.11 ± 0.04 3.83 ± 0.01
Oleic C18:1 16.8 ± 0.47 12.8 ± 0.09
Linoleic C18:2 70.3 ± 0.60 74.8 ± 0.26
7.11 7.61
Not detected.
Unsaturation ratio = (16:1 + 18:1 + 18:2)/(12:0 + 14:0 + 16:0 + 18:0).
20 30 40 50 60 70
Temperature (˚C)
Apparent viscosity (Pa.s)
Fig. 1. Effect of temperature increasing (n) and decreasing (m) on the
apparent viscosity at shear stress 10 Pa.
0.1 1 10 100
shear stress (Pa)
Apparent viscosity (Pa.s)
Fig. 2. Effect of shear stress increasing (Hollow symbols) and
decreasing (filled symbols) on the apparent viscosity of O. ficus indica
at various temperatures.
434 M. Ennouri et al. / Food Chemistry 93 (2005) 431–437
state of the oil. The crude oil before shearing was a suspen-
sion in which dispersed phase was constituted of aggre-
gated particles of fatty acids with a high melting point,
as described above. These aggregates resisted the flow
and this explained the initial increase of viscosity. They
were destroyed quickly by the shearing. Consequently, a
small decrease of viscosity and a stable suspension consti-
tuted of smallest particles were observed. So the flow be-
came Newtonian when shear stress was above 2 Pa.
These results ratified the hypothesis of the experi-
ments described in the previous paragraph and were in
accordance with previous works. Matveenko, Kirsanov,
& Remizov (1995) identified two different parts of each
flow curve as the high shear rate region and the low
shear rate region, separated by a break point. Moreover,
Geller & Goodrum (2000) showed that dynamic viscos-
ity of vegetable oils was shear-independent at high shear
rates (above 6 s
). Our measures displayed a Newto-
nian flow in that shear rate range. The same effect was
observed for both prickly pear seed oils. The values of
Newtonian viscosity are given in Fig. 3.
3.3.3. Dynamic tests
To eliminate the influence of the shearing and to ana-
lyze only the effect of the temperature, rheological mea-
sures were conducted in oscillatory mode with up and
down cycles of temperature. The reason for oscillatory
rheological tests was that the very low shear stress did
not destroy the structural state of sample. Curves pre-
sented in Fig. 4 showed that the loss modulus G00 was
superior to the storage modulus G0. As expected the val-
ues for G0and G00 characterized rheological behaviour of
a disorganized state at all experimental temperatures.
The effect of the temperature was visible until 55 C.
Rheological dynamic parameters, G0and G00 , remained
steady between 55 and 70 C because both palmitic
and stearic acids melted; consequently, no more change
was observed. At 70 C, there were no more aggregates
in the oil. As a consequence, this medium was totally li-
quid. During cooling, a recrystallization occurred. The
recrystallization led to the formation of fat crystals hav-
ing similar size and caused a homogeneous organization
in the whole volume. The result was that the storage
modulus G0was more raised in cooling than in heating
due to greater organization of medium than in the initial
state. The variations of loss tangent were consecutive to
changes of G0and G00.
In previous studies on fat crystal networks, workers
observed that a logarithmic linear relationship existed
between elastic modulus G0and the solid fat content
(Narine & Marangoni, 1999). This result was not ob-
served but in the studied samples of prickly pear seed
oil, which were very different from a fat crystal network.
The content of solid fats in these samples was significant
but very low. So the values of dynamic parameters were
very weak and did not permit more observation. This re-
sult is confirmed by the measurements from laser light
3.4. Microscopy
The analysis of rheological behaviour was confirmed
by light microscopic observations. The crude oil of O.
stricta showed large aggregates of fat crystal particles
of nearly 60 lm(Fig. 5(a)). The same oil, observed after
shearing (Fig. 5(b)), revealed small particles dispersed
over all the ranges of vision; the aggregates, which were
visible in crude oil, disappeared. The same result oc-
curred with oil treated by heating to 70 C and then
shearing. This structural state of suspension was in
agreement with the Newtonian behaviour observed after
shearing on the flow curves.
The crude oil of O. ficus indica displayed the same
microscopic behaviour but the size of aggregates was
smaller (30 lm, data not shown).
20 30 40 50 60
Temperature (˚C)
Apparent viscosity (Pa.s)
Fig. 3. Viscosity of prickly pear seed oil at different temperatures in
the stable linear zone (s> 2 Pa). j=O. stricta seed oil, h=O. ficus
indica seed oil.
20 30 40 50 60 70
Temperature (˚C)
G' G" (Pa)
Tan (G" /G’)
Fig. 4. Changes in the storage modulus GÕ(nm), in the loss modulus
G00 (hj) and in tangent loss angle (sd) with increasing (nsh) and
decreasing temperatures (md n) for O. ficus indica at 1 Hz in
frequency and 0.3 Pa in shear stress.
M. Ennouri et al. / Food Chemistry 93 (2005) 431–437 435
3.5. Particle size distribution
With the object of analysing the particles in suspen-
sion, the crude oil of O. stricta was tested with a Mal-
vern Mastersizer. The particle size distribution
highlighted a main peak in which the mean diameter
of particles, d
, was 70 lm(Fig. 6). The peak centred
at 7 lm only represented 2.87% of total volume, so is
of minor importance.
4. Conclusions
The purpose of this research was to determine the phys-
icochemical properties, fatty acid composition and rheo-
logical behaviour of seed oils from two species of prickly
pear growing in Tunisia: O. ficus indica and O. stricta.
Seeds represented about 18–20% of peeled fruits. The
oil was extracted from ground seeds with hexane (yield
nearly 11%). The refractive index and densities were sim-
ilar for both species. Iodine values and saponification
numbers indicated little difference in qualitative compo-
sition and quantitative fatty acid content between both
oil samples.
Fatty acid analysis by GC–MS revealed (in both Opun-
tia oils) four major fatty acids: palmitic, stearic, oleic and
linoleic acid, previously reported in vegetable oils. Palmit-
oleic acid was present in low quantities. O. stricta oil con-
tained also traces of lauric and myristic acids. Both oils
were exceptionally rich in linoleic acid, (up to 70%) and
their contents of unsaturated fatty acids were high, (about
88%). The fatty acid composition of prickly pear oil was
close to those of sunflower and grapeseed oils. These char-
acteristics illustrated the interest of prickly pear as a nat-
ural source of edible oil containing essential fatty acids
and as an economic utility for Tunisia.
The rheological properties were analysed. Variations
of viscosity and viscoelasticity parameters were studied
across heating and cooling cycles from 20 to 70 C. For
the investigation on viscosity, a consecutive cycle of tem-
perature was applied. The flow curves were established
with up and down cycles of shear stress at different tem-
peratures. Simultaneously, a crude oil sample, a shearing
oil sample and an oil sample submitted to a treatment by
heat at 70 C were observed with a contrast phase micro-
scope. Lastly, a crude oil was investigated by laser light
scattering to obtain the particle size distribution.
The convergence of rheological measurements and
microscopic observations highlighted the structural state
of prickly pear seed oil: the crude oil contained large
aggregates of unmelted fatty acids. The mean size of
aggregates (by microscopy) was 60 and 30 lm for O.
stricta and O. ficus indica, respectively.
The measurment by laser light scattering showed a
peak formed by particles with mean diameter of 71.8
lm, corresponding to 14% of the total volume of the
O. stricta crude oil.
The crude oil of prickly pear seed contains aggregated
fatty acid crystals. Shearing and temperature destroyed
the aggregates and homogeneous suspension developed:
this suspension, with a stable structural state, had New-
tonian flow at high shear stress.
Fig. 5. Contrast phase microscopy of crude (a) and sheared oil (b) of O. stricta. Magnification is 400·, scale bar = 15 lm.
0.01 0.1 1 10 100 1000
particle size (
Volume (%)
Fig. 6. Particle size distribution of the O. stricta seed oil, obtained by
laser light scattering.
436 M. Ennouri et al. / Food Chemistry 93 (2005) 431–437
The findings shown in this work raise the nutritional
value of these under-exploited plants, especially in semi-
arid regions of Tunisia, where conventional crops are
We thank Mr. Hammami Mohamed responsible for
U.S.C.R. spectrometry for chromatographic analyses.
Association of Official Analytical Chemists (1984). Official methods of
analyses. Washington, DC: Association of Official Analytical
Association of Official Analytical Chemists (1990). Official methods of
analyses. Washington, DC: Association of Official Analytical
American Oil Chemists Society (1993). Official methods and recom-
mended practices of the American Oil ChemistsÕSociety. Cham-
paign, IL: American Oil ChemistsÕSociety.
Balogun, A. M., & Fetuga, B. L. (1986). Chemical composition of
some under-exploited leguminous crop seeds in Nigeria. Journal of
Agriculture and Food Chemistry, 38, 189–192.
Bustos, E. O. (1981). Alcoholic beverage from Chilean Opuntia ficus
indica.American Journal of Enology and Viticulture, 32(3), 228–229.
Coskuner, Y., & Tekin, A. (2003). Monitoring of seed composition of
prickly pear (Opuntia ficus indica L.) fruits during maturation
period. Journal of the Science of Food and Agriculture, 83(8),
Di Cesare, L. F., & Nani, R. (1992). Analysis of volatile constituents of
prickly pear juice (Opuntia ficus indica var. Fructa sanguineo). Fruit
Processing, 2(1), 6–8.
El Kossori, R. L., Villaume, C., El Boustani, E., Sauvaire, Y., &
Mejean, L. (1998). Composition of pulp, skin and seeds of prickly
pears fruit (Opuntia ficus indica sp.). Plant Foods for Human
Nutrition, 52, 263–270.
Espinosa, J., Borrocal, R., Jara, M., Zorilla, C., & Medina, J. (1973).
Quelques proprie
´s et essais pre
´liminaires de conservation des
fruits et du jus de figue de barbarie (Opuntia ficus indica). Fruits, 28,
Ewaidah, E. H., & Hassan, B. H. (1992). Prickly pear sheets: a new
fruit product. International Journal of Food Science and Technol-
ogy, 27, 353–358.
Fisher, C. H. (1995). n-fatty acids: comparison of published densities
and molar volumes. Journal of American Oil Chemistry Society, 72,
Flath, R. A., & Takahashi, J. M. (1978). Volatile constituents of
prickly pear (Opuntia ficus indica Mill.), de Castilla variety. Journal
of Agriculture and Food Chemistry, 26, 835–837.
Formo, M. W., Jungermann, E., Norris, F. A., & Sontag, N. O. (1979)
(4th ed.. In D. Swern (Ed.). BaileyÕs industrial oil and fat products
(Vol. 1, pp. 189). New York: Wiley.
Geller, D. P., & Goodrum, J. W. (2000). Rheology of vegetable oil
analogs and triglycerides. Journal of American Oil Chemistry
Society, 77(2), 111–114.
Hassan, M., Blanc, P. J., Pareilleux, A., & Goma, G. (1995).
Production of cocoa butter equivalents from prickly pear juice
fermentation by an unsaturated fatty acid auxotroph of cryptococ-
cus curvatus grown in batch culture. Process Biochemistry, 30(7),
Hegwood, D. A. (1990). Human health discoveries with Opuntia sp.
(Prickly pear). Journal of Horticultural Science, 25, 1515–1516.
Karlesind, A. & Wolff, J. P. (1992). Manuel des corps gras. AFECG,
Majdoub, H., Roudesli, S., Picton, L., Le Cerf, D., Muller, G., &
Grisel, M. (2001). Prickly pear nopals pectin from Opuntia ficus
indica physico-chemical study in dilute and semi-dilute solutions.
Carbohydrate Polymers, 46, 69–79.
Matveenko, V. N., Kirsanov, E. A., & Remizov, S. V. (1995).
Rheology of highly paraffinaceous crude oil. Colloids and Surfaces
A, 101, 1–7.
McGarvie, D., & Parolis, H. (1979). The mucilage of Opuntia ficus
indica.Carbohydrate Research, 69, 171–179.
Medina-Torres, L., Brito-De La Fuente, E., Torrestiana-Sanchez, B.,
& Katthain, R. (2000). Rheological properties of the mucilage gum
(Opuntia ficus indica). Food Hydrocolloids, 14, 417–424.
Narine, S. S., & Marangoni, A. G. (1999). Microscopic and rheological
studies of fat crystal networks. Journal of Crystal Growth, 198/199,
Noureddini, H., Teoh, B. C., & Davis Clements, L. (1992). Densities of
vegetable oils and fatty acids. Journal of American Oil Chemistry
Society, 69(12), 1184–1188.
Oomah, B. D., Ladet, S., Godfrey, D. V., Liang, J., & Girard, B.
(2000). Characteristics of raspberry seed oil. Food Chemistry, 69,
Ramadan, M. F., & Morsel, J. T. (2003). Oil cactus pear (Opuntia
ficus-indica L). Food Chemistry, 82, 339–345.
Saenz, C. (2000). Processing technologies: an alternative for cactus
pear (Opuntia spp.) fruits and cladodes. Journal of Arid Environ-
ments, 46, 209–225.
Salvo, F., Galati, E. M., Lo Curto, S., & Tripodo, M. M. (2002). Study
on the chemical characterization of lipid composition of Opuntia
ficus-indica L. seed oil. Rivista Italiana delle Sostanze Grasse,
79(11), 395–398.
Sawaya, W. N., & Khan, P. (1982). Chemical characterization of
prickly pear seed oil, Opuntia ficus indica.Journal of Food Science,
47, 2060–2061.
Sawaya, W. N., Khatchadorian, H. A., Safi, W. M., & Al-Mohammad,
H. M. (1983). Chemical characterization of prickly pear pulp,
Opuntia ficus indica, and the manufacturing of prickly pear jam.
Journal of Food Technology, 18, 183–193.
Sawaya, W. N., Khalil, J. K., & Al-Mohammad, M. M. (1983).
Nutritive value of prickly pear seeds, Opuntia ficus indica.Plant
Foods for Human Nutrition, 33, 91–97.
Stintzing, F. C., Schieber, A., & Carle, R. (2001). Phytochemical and
nutritional significance of cactus pear. European Food Research
Technology, 212, 396–407.
Tan, C. P., & Che Man, Y. B. (2000). Differential scanning
calorimetric analysis of edible oils:comparison of thermal proper-
ties and chemical composition. Journal of American Oil Chemistry
Society, 77(2), 143–155.
Teles, F. F. F., Whiting, F. M., Price, R. L., & Borges, V. E. L. (1997).
Protein and amino acids of nopal (Opuntia ficus indica). Revista
Ceres, 44(252), 205–214.
Trachtenberg, S., & Mayer, A. M. (1981). Composition and properties
of Opuntia ficus indica mucilage. Phytochemistry, 20, 2665–2668.
Trachtenberg, S., & Mayer, A. M. (1982). Biophysical properties of
Opuntia ficus indica mucilage. Phytochemistry, 21(12), 2835–
Uchoa, A. F., Souza, P. A. S., Zarate, R. M. I., Gomez-Filho, E., &
Campos, F. A. P. (1998). Isolation and characterization of a reserve
protein from the seeds of Opuntia ficus indica.Brazilian Journal of
Medical and Biological Research, 31, 757–761.
Valeri, D., & Meirelles, A. J. A. (1997). Viscosities of fatty acids,
triglycerides, and their binary mixtures. Journal of American Oil
Chemistry Society, 74(10), 1221–1226.
M. Ennouri et al. / Food Chemistry 93 (2005) 431–437 437
... The viscosity of mayonnaise samples prepared with NS oil was higher than the control sample. A decrease in the amount of linoleic and unsaturated fatty acids in oil may be the cause of the decrease in the viscosity value of mayonnaise samples (Ennouri et al., 2005). Colour is the primary criterion consumers use to accept the product (Fernandesa and Mellado, 2018). ...
Full-text available
The stability of lipid oxidation of fat-rich food products is one the most important factors to preserve the quality of food products. Therefore this study aimed to enhance the oxidative stability of Nigella sativa (NS) oil for 15 days at 50°C, by using different concentrations of extracts from olive leaves (OL), tomato by-product (TP), orange peel (OP) and water melon peel (WP) as naturally bioactive compounds, in addition to assess the quality of mayonnaise containing NS oil as a functional ingredient. The natural phenolic compounds of these agro-industrial wastes were extracted and identified using HPLC. The results showed that OL extract had the highest total phenolic content (121.09 mg GAE/g dw) which represented about 1.76, 3.91 and 13.34 times higher than the phenolics in the TP, OP and WP extracts, respectively. The results of the oxidative stability measurements indicated that the addition of all extracts to NS oil retarded the oxidative rancidity compared to the control as measured by the peroxide value, p-anisidine value, and thiobarbituric acid. Infrared analysis demonstrated the antioxidant power of the OL extract at 400 ppm and the TP at 600 ppm in preventing rancidity conditions, which were similarly effective as the synthetic antioxidant Tertiary-butyl hydroquinone (TBHQ) (200 ppm). This demonstrated the potential for using them as natural antioxidants to prevent rancidity in stored oil. The results of quality and sensory evaluation of NS oil mayonnaise showed an increase in viscosity and a change in colour parameters that were imperceptible to the human eye as the ΔE values were less than 3, and all mayonnaise products were "accepted" by the panelists.
... 74%) reported by ElHachimi et al. (2015).Benattia et al. (2019) found lower oil contents (6.42%) in prickly pear seeds collected in the region of Relizane (Algeria). Other studies reported that the oil content of prickly pear seed ranged from 4.60 to 17.2%(Coşkuner and Tekin, 2003;Gharby et al., 2020;Liu et al., 2009).Ennouri et al. (2005) studied two Opuntia species from the Sfax region (Tunisia); they found an oil content of 10.90% and 11.05% for the seeds of O. ficus-indica and O. strica respectively. Other studies have shown that the yield percentage of extracted oil from Opuntia dillenii is about 6 to 7%(Alsaad et al., 2019;Bouhrim et al., 2021). ...
The Cactus Opuntia spp. plant is important to Morocco's arid and semi-arid regions. The edible and cosmetic oil from prickly pear fruit seeds is very prized. Since Dactylopius Opuntiae first appeared in Morocco in 2014, hundreds of hectares of cactus have been devastated, causing environmental and socio-economic costs. Eight D. Opuntiae resistant varieties were selected, multiplied and transplanted throughout Morocco, as part of the government's nationwide cactus rehabilitation program. This research evaluated the production and fatty acid composition of the seed oil of these varieties. Oil extraction was carried out with the Soxhlet method using hexane and by mechanical screw press. The crude seed oil content obtained by hexane extraction ranged from 9.54% to 16.44% (w/w). Mechanical screw extraction recovered half the seeds' oil. The fatty acid profiles showed that the oils were highly unsaturated; UFA fraction represented 76.31 to 82.63% of total FA and UFA/SFA ratio of 3.48 to 5.36. Linoleic acid was the dominant and represented 61.50% to 68.35% of total FA. These results highlight the importance of cochineal-resistant cactus varieties as oil sources and alternatives to those destroyed and still threatened by the harmful scale pest that appeared in more than 20 countries.
... Dillenii is a prickly pear variety, the fruit is a small haw, and it is formed by a deep red-purple thick peel and a red-purple pulp with abundant small seeds [14] (Fig. S1). In our previous works, we have characterized the fatty acid composition of Opuntia stricta seeds [15] which is rich in polyunsaturated fatty acids, in antioxidants, and in vitamin E. The seeds oil is used as a cutaneous application or incorporated into cosmetic formulations for its rejuvenating and anti-wrinkle properties. Opuntia stricta flowers are also characterized by antimicrobial and interesting biological activities [16,17]. ...
Full-text available
The formulation of a new functional beverage from Opuntia stricta juice enriched with whey cheese was investigated. Five beverages were developed with different percentages of juice. The storage stability was evaluated at 4 °C during 60 days in terms of physicochemical analysis (pH, acidity, total, and reducing sugar). The prepared beverages have a red color and a highly acceptable taste, the overall acceptability varies from 6.12 to 6.80 and from 7.16 to 8 respectively for the two categories of consumers 10–25 and over 25 years old. The relation between acceptability of beverages (for two categories of consumers) and sensory parameters (color, juice percentage, taste, and texture) was modelized using linear regression model with a correlation coefficient (R²) of 72.9% and 70.5% respectively for consumers 10–25 and over 25 years old. In this vein, the beverages were appreciated differently according to the age range of consumers (10–25 years or over 25 years old). A mathematical relationship between the responses (pH, acidity, reducing, and total sugars) and covariates (storage period and juice concentration) was obtained, described by first-order polynomial equations with an R² of 87%, 83%, 89.5%, and 88.7% respectively for pH, acidity, reducing, and total sugar. The study showed that the drinkable beverage based on whey and Opuntia stricta juice with a proportion of juice varying from 35 to 25% is the best regarding sensory properties and physicochemical stability.
... This fact may be related to the chemical composition of pitaya seeds, which have a large protein reserve. While the seeds of Opuntia sp., belonging to the same family as pitayas, contain 50 g of protein kg -1 of seeds (ENNOURI et al., 2005), pitaya seeds have 206 g kg -1 of seeds (VILLALOBOS-GUTIÉRREZ et al., 2012). For this reason, during germination under water stress conditions, there was probably a higher hydrolysis of proteins into amino acids than hydrolysis of starch into sugars. ...
Full-text available
The use of mitigating agents to minimize the deleterious effects of water stress is a promising alternative for plant species, especially during germination and initial seedling development. Thus, the objective was to evaluate the effect of different pre-germination treatments as mitigating agents of water stress during germination and initial development of pitaya seedlings of the species Hylocereus undatus and H. costaricensis. The experiment was carried out in a completely randomized design, in a 2 x 6 factorial scheme, corresponding to two pitaya species and six pre-germination treatments (T1 = 0.0 MPa (control), T2 = -0.2 MPa (water stress); T3 = hydropriming + water stress; T4 = gibberellic acid + water stress; T5 = salicylic acid + water stress and T6 = thiamethoxan + water stress) with four replicates of 50 seeds. The variables analyzed were germination, germination speed index, shoot and primary root lengths, total dry mass, total soluble sugars and total free amino acids. The water potential of -0.2 MPa is limiting for germination and initial growth of H. costaricensis and H. undatus, with H. undatus being more tolerant to water stress in the germination phase. Pre-germination treatments with hydropriming, gibberellic acid, salicylic acid and thiamethoxan improve the physiological performance of H. costaricensis seeds, with gibberellic acid being the best attenuator of water stress. Gibberellic acid improves the physiological performance of H. undatus seeds under water deficit conditions. Keywords: Cactaceae; Mitigation; Gibberellic acid; Hydropriming; Salicylic acid
... The prickly pear rather than cladode may be considered as a superfood, because apart of antioxidants it possesses a significant variety of other active components. Its seed oil contains more ω-6 fatty acids than sunflower oil -70.29% against 60.15% (Ennouri, 2005). The fruit also is rich in vitamins, such E, C and K1, and sterols, mainly β-sitosterol and camesterol (Ramadan, 2003). ...
Full-text available
Hoy en día, muchos productos alimenticios se investigan con el fin de establecer sus propiedades medicinales, componentes activos y las posibles aplicaciones médicas para la prevención o el tratamiento de diferentes enfermedades. En el presente trabajo hemos resumido algunos avances en la investigación del potencial medicinal de 4 alimentos tradicionales mexicanos: nopal, chile, canela y agave. Los resultados han demostrado que los 4 merecen estar presente a diario en la dieta de los mexicanos.
... Linoleic acid is the major fatty acid in the seeds and pulp of the prickly pear oil, followed by palmitic and oleic acids [6]. According to Ennouri et al. [75], the primary fatty acids found in prickly pear seed oil are C16:0, C18:0, C18:1, and C18:2. The unsaturated fatty acids concentration was 88.5% and 88.0% for Opuntia ficus-indica and Opuntia stricta, respectively, with an outstanding level of linoleic acid, up to 70%. ...
Full-text available
Prickly pear plant is widely cultivated in arid and semi-arid climates. Its fruits are rich inpolyphenols, proteins, vitamin C, minerals, fatty acids, and amino acids. The oil extracted from theseeds also has a significant proportion of linoleic acid (ω6) and might be employed as a therapeuticraw material. The potential of enhancing fruit yield, increasing bioactive compounds of the fruitpulp, and improving the unsaturated fatty acid content of prickly pear oilseed by using the foliarapplication of brassinolide as a plant growth regulator was the main goal of this study. Prickly pearplants were foliar sprayed with a brassinolide solution at concentrations of 0, 1, 3, and 5 mg L−1. Theplant performance was significantly improved following brassinolide applications, as compared withuntreated plants. The plants subjected to 5 mg L−1 application exhibited 183 and 188% stimulationin the fruit yield, and 167 and 172% in the seed yield for the first and second seasons, respectively.The highest concentration of phenolic, flavonoid, protein, vitamin C, and maximum antioxidantactivity in the fruit pulp was observed following 5 mg L−1 brassinolide treatment. The oil yieldhas been increased by 366 and 353% following brassinolide at a 5 mg L−1 level over control plants.Linoleic, oleic, and palmitic acids are the major components in prickly pear seed oil. Brassinolidefoliar spraying induced an alternation in the fatty acid profile, as linoleic and oleic acids exhibited 5and 4% higher following 5 mg L−1 application as compared with untreated plants. In conclusion,the treatment of 5 mg L−1 brassinolide improved the growth and quality of prickly pear plants byboosting fruit and seed yields, increasing active component content in the fruit pulp, improvingmineral content, and increasing oil production and linoleic acid proportion.
Full-text available
Opuntia ficus indica L (Cactaceae), is commonly employed in Morocco as an alternative medicinal approach for managing diabetes mellitus (DM). The objective of the study is to explore and examine novel mechanism underlying the antidiabetic activity of Opuntia ficus indica seed oil (OFIO), which has shown promising potential in managing diabetes, but the exact mechanisms responsible for its antidiabetic effects remain unclear. Therefore, the current study explores the antihyperglycemic effectof OFIO, the in vitro antioxidant properties, and the antiglycation activity of OFIOof hemoglobin (Hb) model. The total phenolic levels were determined using Folin– Ciocalteu colorimetric approach and total flavonoid levels were determined using colorimetric assay with aluminum chloride. The effect of antihyperglycemia was evaluated using the inhibitory effect of pancreatic α-amylase activity both in vitro and in vivo using Alloxan induced-diabetic rats and the glucose uptake in an isolated rat hemidiaphragm in vitro model. The antioxidant activity was studied using the DPPH Radical scavenging activity test. In addition, the antiglycation activity of OFIO was also tested in-vitro using hemoglobin model. The outcomes derived from this research have demonstrated that OFIO exhibited potent α-amylase inhibitory activity in vitro (p < 0.01; IC50 values of 4.24 ±0.18 mg/ml, and 4.05± 0.08 mg/ml respectively) and in vivo using Alloxan induced-diabetic rats. In contrast, OFIO has no effect on glucose uptake by the rat diaphragm muscle as compared to negative control. In addition, OFIO showed a significant antioxidant and hemoglobin antiglycation activities (p<0.001) with an IC50 value of 2.05± 0.06 mg/ml, and 0.485± 0.017 mg/ml, respectively.The findings of this study suggest that is OFIO has promising antidiabetic activity. Keywords: Opuntia ficus indica, diabetes mellitus, α-amylase, antiglycation, antioxidant, hemidiaphragm
This chapter discusses current issues, such as the increased amount of high-quality protein and bioactive peptides obtained by hydrolysis and the phenolic compounds that ameliorate some biomarkers associated with some illnesses. These positive effects include antioxidant, antiproliferative, antithrombotic, anti-diabetic, and anti-obesity treats, documented in different experimental models. Furthermore, industrial applications, including cosmetics, biofilms, and composites, and the production of elastic networks to improve food texture have been developed, not only with the seeds but also with the residues and subproducts of this plant.
Fruits are typically seen, as a natural source of health-promoting compounds concentrated, mainly in their peel and pulp, though very little is known concerning lipochemical and antioxidant properties found in their respective seeds. For figs (Ficus cacrica L.), a traditional food staple for a healthy diet in Middle Eastern and North African countries, seeds are usually discarded during fruit processing and have not received particular attention. Although it remains the less studied component of Ficus carica L., the few available reports showed that the fig seeds present a significant oil yield reaching up to 30% with a very high unsaturation level (88%) alongside a promising antiradical scavenging potency. However, the varietal effect and the pollination impact on the lipochemical attributes of fig seeds oil are thus far gone unheeded. Some recent attempts were undertaken to examine these aspects and significantly affected the seed yield and its oil quality. The present chapter investigates the nutritional quality of fig seed oil as a minor oil from atypical plant sources. This chapter is in the scope of the circular economy in the fruit processing sector as there is an increasing demand for novel sources of vegetable oil, particularly unexploited fruit seeds that constitute an essential part of the waste during processing. It concludes that the fig seeds are not only a novel source of oil holding polynutrients with potential health-promoting effects but also lessen the waste discarding problem of the agro-based industry.
Full-text available
Some quality parameters were evaluated in Opuntia ficus-indica seed oil samples obtained from fruit wastes harvested in S.Cono (Catania- Italy). The seeds (12-16% of the fruit peel) were submitted to hexane extraction, obtaining 8-9% oil, on seed dry weight. The tests carried out on this oil gave the following results: fatty acids content (as oleic acid): 2.5%, iodine number: Wijs (105.5), peroxide number (10meq O2/Kg), UV absorption: K232 = 3.15; K268 = 0.22; δK= + 0.01, all in agreement with the characteristics of other common vegetable oils. The acidic fraction revealed an high degree of unsaturation (82.3 %) with monounsatured and polyunsatured contents of 21.0 % and 61.3 %, respectively. The sterolic fraction was composed mainly of β-sitosterol (61.4%), campesterol (16.5 %), stigmasterol (4.2 %) and other more unsatured sterols (6.2 %). Alcanolic fraction contained mainly hexacosanol (73.7%), along with low quantities of docosanol (10.7%) and octacosanol (8.1%) and smaller amounts of other components. Among triterpenic alcohols, the most abundant component was found to be 24-methylcycloarthenol (34.2%), followed by cycloarthenol (29.3%), and β-amyrin (2.2%). Based on these results, Opuntia ficus-indica seed oil appears to be a good potential source of alimentary oil.
The mucilage extracted from the cladodes (modified stems) of Opuntia ficus-indica contains residues of d-galactose, d-xylose, l-arabinose, l-rhamnose, and d-galacturonic acid. Seasonal variation in the sugar composition of the mucilage has been investigated. Fractionation studies indicate that the mucilage is essentially homogeneous. The rate of release of the constituent sugars and the change in optical rotation on mild hydrolysis coupled with the results of chromic acid oxidation suggest that the mucilage contains α-arabinofuranosyl, β-xylopyranosyl, β-rhamnopyranosyl, β-galactopyranosyl, and α-galactopyranosyluronic acid residues. The results also suggest a core containing galacturonic acid, rhamnose, and galactose, to which xylose and arabinose are attached in peripheral positions.
The purified mucilage from Opuntia ficus-indica is a high MW polysaccharide which behaves as a polyelectrolyte. Viscosity of its solution is dependent on the Ca2+ ion concentration and on pH, being greatest at alkaline pH. The sedimentation coefficient was dependent on concentration. The molecule had an estimated axial ratio of 256 in water, and this was reduced at low pH and in the presence of high concentrations of Ca2+. The molecule was studied with light scattering and CD techniques and its UV spectrum was recorded. All these parameters were influenced by pH and by ion concentration. The gelation properties also changed with pH and with Ca2+ giving dense gels in its presence and loose ones in its absence. The results are interpreted in terms of changes in conformation of the molecule, changes in Ca2+ binding and degree of ionization of the molecule. An attempt is made to relate the molecular properties to the physiological function of the mucilage in the calcium and water economy of the plant.
The water soluble fraction of peeled prickly pear nopals called native sample (NS) has been characterised mainly by SEC/MALLS analysis. Two main components have been identified: one with high average molar mass (Mw of 13×106gmol−1) called the high weight sample (HWS), the other being a low Mw fraction (LWS). After extensive ultra filtration of NS, isolated HWS and LWS are obtained. From sugar composition analysis, HWS has been found to be a pure polysaccharide, without protein of the pectin family. Moreover, HWS contains a low amount of charged sugar. The conformation of HWS has been discussed using molar masses, gyration radii and viscometry results and LWS has been evidenced as a protein. Rheological behaviour is reported to give an initial understanding of the system's behaviour. The effect of the degree and purification and added monovalent and divalent salts were investigated, The low charge density of the polymer backbone resulted in interesting viscosity stability even in the presence of salts.
The rheology of a highly paraffinaceous crude oil has been studied by a rotary viscometer. The influence of the mechanical history of the oil sample on the flow curve form was examined. The system under investigation was found to be pseudoplastic with clearly pronounced thixotropic properties, which are indicated by the hysteresis phenomenon between the data obtained on increasing and decreasing the shear rateγ˙. At least two different parts of the flow curve were observed at low and high shear rates. We assume that two different mechanisms of the energy dissipation referred to these parts of the flow curve >(γ˙). We consider the Casson equation as the most appropriate within the high shear rate region, in spite of the fact that the Herschel-Bulkley equation often fits the experimental data better. The choice of the Casson model is confirmed by the regular changes in the rheological parameters of this equation. Moreover, the agreement of the flow curves with the Casson equation increases with increasing oil structure breakdown.