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The effect of consecutive steps of refining on squalene content of vegetable oils


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The aim of this study is to evaluate the effect of refining steps on the squalene content of some vegetable oils. A comparison has been made between the crude oils and consecutive steps of refining process (neutralization, bleaching, deodorization, winterization) in the amounts of squalene of the oil samples. Among the oils, virgin and refined olive oils contained higher amounts of squalene. A mean of 491.0 ± 15.55mg/100g squalene was found in virgin olive oil samples. While appreciable quantities of squalene has been reduced during refining, considerable level of squalene were still present in refined olive oils (290.0 ± 9.89mg/100g). The squalene content of crude seed oils varied from 13.8 ± 0.39mg/100g to 26.2 ± 0.08mg/100g as average. It has been determined that refining process reduced the level of squalene in examined oils. The highest reduction in squalene content of the oils was detected during deodorization. The effect of refining steps on the amount of squalene in vegetable oils was found to be significant (p < 0.05). Olive oil has been considered an important source of squalene, even after it has been refined, compared to seed oils. KeywordsVegetable oils–Refining–Squalene
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The effect of consecutive steps of refining on squalene
content of vegetable oils
Cevdet Nergiz &Deniz Çelikkale
Revised: 13 November 2010 /Accepted: 22 November 2010 / Published online: 21 December 2010
#Association of Food Scientists & Technologists (India) 2010
Abstract The aim of this study is to evaluate the effect of
refining steps on the squalene content of some vegetable
oils. A comparison has been made between the crude oils
and consecutive steps of refining process (neutralization,
bleaching, deodorization, winterization) in the amounts of
squalene of the oil samples. Among the oils, virgin and
refined olive oils contained higher amounts of squalene. A
mean of 491.0±15.55 mg/100 g squalene was found in
virgin olive oil samples. While appreciable quantities of
squalene has been reduced during refining, considerable
level of squalene were still present in refined olive oils
(290.0±9.89 mg/100 g). The squalene content of crude seed
oils varied from 13.8±0.39 mg/100 g to 26.2±0.08 mg/
100 g as average. It has been determined that refining
process reduced the level of squalene in examined oils. The
highest reduction in squalene content of the oils was
detected during deodorization. The effect of refining steps
on the amount of squalene in vegetable oils was found to be
significant (p<0.05). Olive oil has been considered an
important source of squalene, even after it has been refined,
compared to seed oils.
Keywords Vegetable oils .Refining .Squalene
In recent years, understanding of the positive effect of some
minor components of foods on human health has encour-
aged the scientific research on this topic. A great interest has
been on the Mediterranean populations who have longer life
and more healthy living. This was due to the their diets as
extra virgin olive oil which is more consumed by this
populations as compared to other countries (Strandberg et al.
Squalene is one of the minor constituents of vegetable
oils and has a role on human health. Epidemiological
studies have shown that it can effectively inhibit chemically
induced colon, lung and skin tumourigenesis in rodents
(Smith et al. 2000). It has been also used in several
cosmetic applications as a solute component in fats because
it is absorbed easily by skin (Üstündağand Temelli 2004).
It was reported that the decreasing risk for various cancers
and reducing serum cholesterol levels has been ascribed to
the squalene in vegetable oils (He et al. 2003). Several
studies have been carried out to obtain squalene hydrocar-
bon from vegetable sources or marine animals by using
different methodologies (Vazquez et al. 2007). Squalene has
been sold in the markets as capsules for the beneficial effect
on human health recently.
Crude vegetable oils contain squalene in the minor
components which are generally constitute 13% of oil.
One of the most important differences between the olive oil
and other vegetable oils is the amount of squalene present
in the oil. Its concentration in olive oil varies between 0.2
and 0.7%, whereas in other edible vegetable oils it
constitutes only 0.0020.03% (Rao et al. 1998). On the
other hand, the techniques of olive growing (Psomiadou
and Tsimidou 1999), oil extraction methods (Nergiz and
Ünal 1990), Olive fruit variety (Draman and Hışıl2005),
C. Nergiz (*)
Department of Chemistry, Faculty of Arts and Sciences,
Fatih University,
34500 Büyükçekmece, Istanbul, Turkey
D. Çelikkale
Department of Food Engineering, Engineering Faculty,
Celal Bayar University,
45140 Muradiye, Manisa, Turkey
J Food Sci Technol (MayJune 2011) 48(3):382385
DOI 10.1007/s13197-010-0190-2
refining process (Owen et al. 2000a) and adulteration of
virgin olive oil with seed oils affect squalene content of the
oils. The amount of squalene in virgin olive oil has also
been considered as an indicator for adulteration.
Despite variable the squalene content found in several
vegetable oils, there is no detailed investigation on the
factors affecting the amount of squalene in vegetable
oils. Among the factors, refining process is important,
since all the crude vegetable oils cannot be consumed
without refining, except good quality virgin olive oil.
The purpose of this study is to investigate the changes in
the amount of squalene in different vegetable oils during
refining process.
Materials and methods
Oil samples were collected from four different commercial
refineries representing for five different vegetable oils as
two replicates. For the analysis, about 150 mL of oil
samples were taken from each refining steps from selected
refineries. The collected oil samples of olive (10), sunflower
seed (10) and rapeseed (10) were refined by conventional
method. Soybean (8) and corn oil (8) samples were refined by
physical method. Their processing conditions were usually
the same as encountered in industry.
Reagents Squalene standard (purity97%) was purchased
from Fluka (Switzerland), Chloroform, diethylether and
hexane (A.C.S. grade) were obtained from Merck (Darmstadt,
Germany). TLC plates (20× 20 cm), pre coated (0.2 mm) with
silica gel 60 F
were obtained from Fluka (Switzerland),
The other reagents were analytical grade.
Equipment A gas chromatograph apparatus (Agilent 6890N
Series Network GC System) was used with a flame -
ionization detector and a capillary column (HP-5.30 m long ×
0.32 i.d.) coated with a 0.25 μm film thickness of liquid phase
(5% phenyl) methylpolysilioxane (Agilent Technology, USA).
Extraction of the unsaponifiable fraction of the oil samples
were conducted IUPAC Method 2.401 (1987). Five gram of
the oil sample was weighed into a flask and 50 mL 1 N
ethanolic potassium hydroxide solution was added. The
mixture was saponified for 1 h under reflux condenser.
After the saponification, 100 mL distilled water was added.
The solution was poured into the a 500 mL separating
funnel and extracted with 50 mL portions of diethyl ether.
The ethereal extracts were combined into the another
decanting funnel and were washed several times with
100 mL portions of distilled water until the wash-water
gave neutral pH. The ether solution was dried over
anhydrous sodium sulfate and evaporated in a rotary
evaporator under vacuum. The residue was dissolved in
1 mL chloroform and applied to the TLC plates, it was
developed with hexane -diethyl ether mixture (80:20, v/v)in
a developing tank. After drying bands were marked by
viewing under UV light at 254 nm. The spot of squalene
with same Rf value of the authentic squalene standard was
scraped off and dissolved with diethyl ether and filtered.
The ethereal solution was evaporated on a water bath by
passing through the nitrogen gas and dissolved in a certain
mL of hexane. The amount of squalene was determined gas
chromatographically and calculated using a calibration
curve of peak heights versus amount of injected squalene
standards. The chromatographic conditions were: initial
oven temperature 180 °C/min then programmed at 8 °C/min
to 270 °C. Injector temperature: 290 °C, detector temperature:
300 °C. Split ratio was 1:50 using hydrogen as carrier gas with
a flow of 1.0 mL/min. One μL sample was injected by
automatic injector (Agilent 7683 ALS series automatic liquid
sampler). Variance analysis (ANOVA) was used statistical
evaluation of the results by using a package programme SAS
Table 1 Changes in squalene content (mg/100 g) of vegetable oils during refining steps
Refining Steps Olive oil
Sunflowerseed oil
Rapeseed oil
Corn oil
Soybean oil
Crude oil 491.0a± 15.55 13.8a± 0.39 26.2a± 0.08 24.7a± 0.40 18.1a± 0.11
Neutralization/Physic. Refining 427.0a± 9.89 (13.0) 12.8b± 0.36 (6.9) 25.7b± 0.11 (1.7) 23.0b± 0.31 (7.3) 15.6b± 0.11 (13.5)
Bleaching 392.5b± 7.77 (7.0) 12.1b± 0.25 (5.3) 24.2c ± 0.10 (5.5) 20.4c±0.29 (11.9) 13.3c± 0.06 (13.0)
Deodorization 315.5c± 6.36 (15.6) 9.9c ± 0.32 (16.9) 22.0d± 0.08 (3.2) ––
Winterization 290.0d± 9.89 (5.2) 9.2d± 0.30 (4.0) 21.1e ± 0.06 (8.7) 25.9b± 0.27 (6.8) 12.5d±0.08 (4.4)
The values given in parenthesis are the % reduction of squalene during each of refining steps
ad Values with same letters within each column are not significantly different (p> 0.05)
Data are mean values of duplicate analysis ± standard deviation
J Food Sci Technol (MayJune 2011) 48(3):382385 383
(Statistical Analysis System) and Duncans multiple range test
(Anon 2001).
Results and discussion
The amounts of squalene in five different crude oil samples
and after each refining steps were given Table 1. Squalene
content of crude oil samples ranged from 13.8±0.39 mg/
100 g to 491.0±15.55 mg/100 g as average. These results
are in agreement with the values reported in the literature
related with squalene content of olive and seed oils
(Gutfinger and Letan 1974; Kiritsakis et al. 1998; Owen
et al. 2000b).
Table 1shows that the average squalene content of the
crude olive oil samples found to be 491.0±15.55 mg/100 g
and decreased for all the refining steps and the largest
reduction has occurred during the deodorization. This was
followed by the neutralization step. The least reduction in
squalene was determined during the vinterization. Squalene
reductions occurred during refining in olive oil samples
were very close. Total reductions during all the stages of
refining was found to be 40.94% as compared to crude
olive oil samples. A significant difference was found
among the refining steps in terms of squalene reductions
statistically (p0.05), which is in agreement with values
reported earlier by Vazquez et al. (2007). They also
reported that deodorization distillate is quite rich in
squalene content and can be used as source of vegetal
squalene. It was recovered from deodorization distillate in
the grade of 93% and 91% purity by supercritical fluid
extraction method (Vazquez et al. 2007).
The amount of squalene in sunflower seed oil was found
to be quite low level as compared to olive oil (Table 1).
Total average reduction for sunflower seed oil samples
during refining process was 32.9%. Table 1shows that the
most reduction has occurred during deodorization. Statisti-
cal evaluation has been made between the average values
pertaining to sunflower seed oil samples and a significant
difference was found among the refining steps in squalene
reductions (P<0.05).
Rapeseed oil samples showed similar results as shown
by olive and sunflower seed oil samples in squalene
reductions during refining process. Total decrease in the
amount of squalene belonging to rapeseed oil samples was
found to be 19.10% averagely (Table 1). The largest
deodorization step. A significant difference was found
among the refining steps in terms of squalene reductions
statistically (P<0.05). In the physical refining process the
amount of squalene content of corn oil was reduced
marginally (Table 1). Total lowering of squalene was
25.90% in corn oil during refining. In contrast to other
oils, the largest decrease was detected during bleaching step
in corn oil. Differences among the refining steps of corn oil
in terms of squalene content reduction were also found to
be significant (P<0.05).
Crude soybean oil contained 18.1±0.11 mg/100 g
squalene as average (Table 1). Similar values in soybean
oil has been reported by Kiritsakis et al. (1998). Squalene
reductions showed differences during physical refining of
soybean oil. In contrast to corn oil, the highest decrease in
amount of squalene has been found to occur during
deacidification process. This differences may be due to
both differences in nature of oils and refining conditions.
Whereas it was the deodorization step that gave largest drop
in squalene content for olive, sunflower seed and rapeseed
oils during chemical refining. Shahidi and Wanasundara
(1999), reported that the most losses of squalene (63%)
occurred during the deodorization step for sea blubber oil
refining. It was thought that high temperature applied
during deodorization caused evaporation and degradation
of squalene.
During the refining of five different types of vegetable oils
the decrease in the squalene level varied from 19,1 to
40,9%. In olive oil which had a higher level of squalene,
losses are relatively higher whereas in the seed oils that
contain lower level of squalene, it was found that the losses
are relatively lower. It has been determined that there is a
considerable difference between natural and refined olive
oil and seed oils in terms of squalene level; furthermore,
olive oil, even it is refined, contains 25 to 30 times more
squalene compared to seed oils. The oils, like olive,
sunflower and rapeseed, processed by chemical refining,
exhibited largest drop in squalene content during deodor-
ization step. In consideration of the fact that only 60% of
squalene that has been taken through a diet, could be
absorbed in human body, it is believed that other types of
vegetable oils could not be considered as a source of
squalene but olive oil.
Acknowledgement This study was supported financially by the
Scientific Research Fund of Celal Bayar University under project
number Müh.2007/037.
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... Among them, the alkaline and high temperature conditions provided by method A allow hydrogen peroxide to decompose to produce hydroxyl radicals (Zhang, Huang, and Pan 2005). Squalene is a substance with a light fragrance and a high antioxidant activity (Nergiz and Celikkale 2011), exhibiting antibacterial function, radiation protection, and heart and cells protective functions (Ramakrishnan et al. 2018), and is widely used in medical engineering and cosmetics. Chemical modifications are important means to improve and broaden these applications. ...
To explore and expand the application of luffa sponge (LS) fiber, three methods were used to chemically modify the LS fibers. The nanoindentation (NI) results show that the LS fibers exhibit a high elastic modulus (12.4 GPa) and hardness (0.7 GPa). Upon treating the fibers with 5%NaOH-5%H 2 O 2 , the NI hardness of the fibers increases by 14.3%. However, when 10%NaOH-20%CH 3 COOH (method B) is used, the hardness of the cell walls decreases by 28.6%. In this case, the removal of amorphous substances from the LS fibers and the swelling reaction of the LS cellulose plays a significant role. Three chemical treatments can partially remove the hemicellulose in the LS fiber. 18%NaOH-1.6%CO(NH 2) 2 (method C) modifies the crystalline structure of the cellulose in the LS fibers. Gas chromatography-mass spectrometry results show that the LS fibers are rich in hexadecanoic acid (14.3%), as well as in substances, such as squalene, oleic acid, and behenic alcohol, which exhibit a high antibiofilm activity. Furthermore, method B increases the total relative content of squalene and squalane in the LS extract by 49.4%; while method C treatment allows LS fibers have the potential to be used to develop phase-change energy storage materials and anti-photoaging disco-loration materials.
... Therefore, it delays the oxidation reactions in various vegetable oils [39] and has anti-cancer and antitumor activity. Recently, squalene has been sold in capsules due to the mentioned beneficial effects, and RODD is a valuable and profitable source [45]. ...
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... Squalene content in crude oil reached 17.68 mg/100 g of oil, values which are comparable to those found in the literature [68]. Almost half (45%) was eliminated in the sequence of stages during the refining, neutralization and winterization steps, which had the most effect on the reduction in the total content of squalene (Table 3). ...
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... Considering the interest shown by this chemical specimen, the purity of the obtained extract and the exceptionally high quantities of side stream material to be managed, the squalene yield, although so low, deserves to be taken in consideration. The presence of squalene in corn oil is also confirmed in the literature [15], in which an amount of about 25 mg/100 g was observed. These data are lower compared to our results (80 mg squalene/100 g) due to the different origin of the corn oil from bioethanol production. ...
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... Therefore, it is necessary to be cautious in the choice of treatment method. In the process of vegetable oil refining, activated carbon and kaolin are often used for the decolorization of vegetable oil (Nergiz & Celikkale, 2011;Sabah et al., 2007). The surface of activated carbon has countless pores and a huge surface area, so it can effectively adsorb chlorophyll, carotene, and other pigment molecules in crude oil (Mansour et al., 2018). ...
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... Chew et al. (2017d) reported the degradation of 8.1% of phytosterols in deodorized kenaf seed oil using optimized parameters had been detected, compared to bleached kenaf seed oil. Nergiz and Celikkale (2011) reported the overall refining process caused a reduction of 40.94% of squalene content in olive oil, and the adverse degradation had taken place during deodorization. ...
Background The refining process aims to eliminate the undesirable components in crude vegetable oil to yield refined oil with improved stability and consumer preference. The refining process can be conducted chemically (degumming, neutralization, bleaching, and deodorization) or physically (without neutralization). Every stage of the refining process has its function to remove particular undesirable compounds that improve the quality of the oils. The implementation of ultrasound technology has attracted interest in edible oil refining as an alternative method to the conventional degumming and bleaching processes. Scope and approach Cavitation is generated through the application of ultrasounds (sound waves more than 20 kHz) to enhance the refining process. This review systematically evaluates and discusses current knowledge on the application of ultrasound technology in edible oil refining. Conventional edible oil refining and ultrasound-assisted refining are reviewed in this article. Key findings and conclusions This ultrasound technology offers several advantages over conventional refining, such as improved oil yield, reduced dosage of materials, and saved cost. This article provides a better understanding of ultrasound mechanism on the oil quality and insightful information to stimulate impending applications in the oil industry.
... Squalene is recovered in fact in the distilled fraction obtained from deodorization in the refining process [10,11]. An investigation showed that the loss of squalene occurs mainly in the deodorization step, but each step of the refining process provides a significant contribution to the total loss, that for olive oil, resulted be around 40% [12]. ...
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Squalene, a key intermediate of cholesterol synthesis, is present especially in olive oil. Regulation of cholesterol metabolism by dietary squalene in man is unknown, even though olive oil users in Mediterranean areas have low serum cholesterol levels. We have investigated absorption and serum levels of squalene and cholesterol and cholesterol synthesis with the sterol balance technique and serum levels of cholesterol precursors in humans during squalene feeding (900 mg/d for 7-30 days). The results were compared with those during cholestyramine treatment. Fecal analysis suggested that about 60% of dietary squalene was absorbed. Serum squalene levels were increased 17 times, but serum triglyceride and cholesterol contents were unchanged. The squalene feeding significantly (P less than 0.05) increased serum levels of free (1.7-2.3 times) and esterified (1.9-2.4 times) methyl sterol contents, while elevations of free and esterified delta 8-cholesterol and lathosterol levels were inconsistent. Cholestyramine treatment modestly augmented free methyl sterol levels (1.3-1.7 times), less consistently than those of esterified ones, while, in contrast to the squalene feeding, serum contents of free and esterified delta 8-cholesterol and lathosterol were dramatically increased (3.3-8 times). Neither of the treatments significantly affected serum plant sterol and cholestanol levels. The squalene feeding had no consistent effect on absorption efficiency of cholesterol, but significantly increased (paired t-test, P less than 0.05) the fecal excretions of cholesterol and its nonpolar derivatives coprostanol, epicoprostanol, and coprostanone (655 +/- 83 SE to 856 +/- 146 mg/d) and bile acids (212 +/- 24 to 255 +/- 24 mg/d), indicating an increase of cholesterol synthesis by about 50%. We suggest that a substantial amount of dietary squalene is absorbed and converted to cholesterol in humans, but this squalene-induced increase in synthesis is not associated with consistent increases of serum cholesterol levels. The clearly increased serum contents of esterified methyl sterols may reflect stimulated tissue acyl CoA: cholesterol acyltransferase (ACAT, EC activity during squalene feeding as these sterols are not esterified in serum.
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Epidemiologic and laboratory studies suggest a cancer protective effect and/or lack of a tumor promoting effect by dietary olive oil as compared with other types of non-marine oils. Squalene, a constituent of olive oil, and a key intermediate in cholesterol synthesis may be regarded as partially responsible for the beneficial effects of olive oil, which include decreased mortality rates among populations with high olive oil consumption. Thus, in this study we have assessed the chemopreventive efficacy of squalene on azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF). In addition, we measured the effect of squalene on serum cholesterol levels in the rats. Male F34 rats (5 weeks old) were fed the control diet (modified AIN-76A) or experimental diets containing 1% squalene or 320 p.p.m. sulindac. Two weeks later, all animals except those in vehicle (normal saline)-treated groups were s.c. injected with AOM (15 mg/kg body wt, once weekly for 2 weeks). At 16 weeks of age, all rats were killed, colons were evaluated for ACF and serum was assayed for the cholesterol levels. As expected, dietary administration of sulindac suppressed ACF development and reduced crypt multiplicity, i.e. number of aberrant crypts/focus. Administration of dietary squalene inhibited total ACF induction and crypt multiplicity by approximately >46% (P < 0.001). Further, squalene at a level of 1% did not show any significant effect on serum cholesterol levels. Our finding that squalene significantly suppresses colonic ACF formation and crypt multiplicity strengthens the hypothesis that squalene possesses chemopreventive activity against colon carcinogenesis.
The effects of a high saturated fat and cholesterol diet, supplemented with squalene or β-sitosterol, on plasma lipoprotein levels in animals were evaluated. Thirty-six male adult F1B hamsters were fed for four weeks on a diet rich in saturated fatty acids composed of 90% chow diet, 10% coconut oil and 0.05% cholesterol. Subsequently, the animals were randomly assigned to three different diet groups (12 animals per group) for four weeks. Group 1 animals consumed the same high-fat diet; group 2 the high-fat diet supplemented with 1% squalene, and group 3 the high-fat diet supplemented with 0.5% β-sitosterol. Results show that squalene does not modify plasma lipoprotein levels. However, in animals that consumed the diet high in saturated fat and cholesterol supplemented with β-sitosterol, plasma levels of total cholesterol, triglycerides and the total cholesterol/HDL-cholesterol ratio decreased by 33%, 49% and 48%, respectively. This reduction in total cholesterol was probably associated with decreased absorption of cholesterol and lower incorporation in chylomicrons and VLDL + IDL. However, cholesterol absorption per se was not measured in this experiment. Plasma triglyceride levels decreased in all lipoprotein fractions. In conclusion, under our experimental conditions, β-sitosterol exerts a hypocholesterolemic and hypotriglyceridemic effect in experimental animals. However, the addition of squalene (1%) to this diet produces no effect on plasma lipoprotein levels.
Effects of processing on constituents of seal blubber oil and that of squalene on oxidative stability of several oils were monitored. The content of α-tocopherol in oil decreased during processing, especially at the bleaching and deodorization steps. There was also a concurrent reduction in the contents of squalene and free fatty acids, especially during deodorization. Oils treated with squalene did not show any improved oxidative stability and in some cases were even less stable.
The unsaponifiable fractions of soybean, cottonseed, coconut, olive, and avocado oils have been studied in detail. The oils differed in the contents of total unsaponifiables, squalene, tocopherols, and sterols and also in the composition of the tocopherol and sterol fractions. The presence of absence of individual unsaponifiable components may help in establishing the identity of each of the investigated oils and in detecting of admixture by another oil.
The purification of squalene from residues of the olive oil deodorization process using countercurrent supercritical carbon dioxide extraction was studied. The raw material employed is a by-product obtained after distillation and ethylation of olive oil deodorizer distillates. This by-product contains mainly squalene and fatty acid esters. The Group Contribution Equation of State was employed to simulate the separation process and to design the experimental extractions, which were carried out in an isothermal countercurrent column, without reflux, at 343 K, pressures ranging from 150 to 230 bar and a solvent-to-feed ratio around 13. Satisfactory agreement was found between experimental and calculated yields and phase compositions, obtaining a raffinate product with a squalene concentration up to 90 wt.%. Finally, the thermodynamic model was employed to find out optimal process conditions to enhance squalene recovery, including partial reflux of the extract product and recirculation of the supercritical solvent in a continuous countercurrent extraction column.
Isolation of minor lipid components from complex lipid mixtures is receiving increased attention due to their biological activity and health benefits. Therefore, properties, health benefits and processing aspects of minor bioactive lipid components were reviewed. Literature solubility data of binary mixtures of minor lipid components (β-carotene, α-tocopherol, stigmasterol and squalene) and supercritical carbon dioxide (SCCO2) were correlated using Chrastil’s equation to determine the general trends of solubility behavior as affected by operating conditions and solute properties. Model parameters were estimated for the whole temperature range (a, b, k) and at each temperature (b′, k′). The slopes of solubility isotherms (k′) were in the range of 4.9–10.6 for β-carotene, 4.5–9.6 for α-tocopherol, 4.9–8.0 for stigmasterol and 7.3–7.6 for squalene. Estimated model parameters were used to compare solubility behavior of these solutes with components of olein glyceride series (oleic acid and triolein) as representatives of major lipid classes found in fats and oils. The findings provide the basis for the study of multicomponent lipid mixtures. Differences in the solubility behavior of components and the effect of operating conditions on solubility can be exploited for fractionation of these multicomponent mixtures to isolate the bioactive minor lipid components.
The role of squalene in olive oil stability was studied for various concentrations and experimental conditions. No effect was found in induction periods of olive oil at elevated temperatures using the Rancimat apparatus. Samples were then stored at 40 and 62 degrees C in the dark, and the extent of oxidation was followed by periodic measurements of peroxide value and conjugated dienes. A concentration dependent moderate antioxidant activity was evidenced which was stronger in the case of olive oil compared to that found for sunflower oil and lard. In the presence of alpha-tocopherol (100 mg/kg) and caffeic acid (10 mg/kg) the contribution of squalene (7000 mg/kg) was not significant. No radical scavenging activity was observed using DPPH(*) in 2-propanol. The weak antioxidant activity of squalene in olive oil may be explained by competitive oxidation of the different lipids present which leads to a reduction of the oxidation rate. Squalene plays a rather confined role in olive oil stability even at low temperatures.
The aim of this study was to evaluate the phenolic antioxidant and squalene content in a range of olive and seed oils. A mean of 290 +/- 38 (SEM) mg squalene/100 g was detected. However, while there was a weak significant difference between extra virgin (424 +/- 21 mg/kg) and refined virgin (340 +/- 31 mg/100 g; P<0.05) olive oils, highly significant differences were evident between extra virgin olive oils (P<0.0001) refined virgin olive oils (P<0.0001) and seed oils (24 +/- 5 mg/100 g). While seed oils were devoid, on average, the olive oils contained 196 +/- 19 mg/kg total phenolics as judged by HPLC analysis, but the value for extra virgin (232 +/- 15 mg/kg) was significantly higher than that of refined virgin olive oil (62 +/- 12 mg/kg; P<0.0001). Appreciable quantities of simple phenols (hydroxytyrosol and tyrosol) were detected in olive oils, with significant differences between extravirgin (41.87 +/- 6.17) and refined virgin olive oils (4.72 +/- 215; P<0.01). The major linked phenols were secoiridoids and lignans. Although extra virgin contained higher concentrations of secoiridoids (27.72 +/- 6.84) than refined olive oils (9.30 +/- 3.81) this difference was not significant. On the other hand, the concentration of lignans was significantly higher (P<0.001) in extra virgin (41.53 +/- 3.93) compared to refined virgin olive oils (7.29 +/- 2.56). All classes of phenolics were shown to be potent antioxidants. In future epidemiologic studies, both the nature and source of olive oil consumed should be differentiated in ascertaining cancer risk.
In the Mediterranean basin, olive oil, along with fruits, vegetables, and fish, is an important constituent of the diet, and is considered a major factor in preserving a healthy and relatively disease-free population. Epidemiological data show that the Mediterranean diet has significant protective effects against cancer and coronary heart disease. We present evidence that it is the unique profile of the phenolic fraction, along with high intakes of squalene and the monounsaturated fatty acid, oleic acid, which confer its health-promoting properties. The major phenolic compounds identified and quantified in olive oil belong to three different classes: simple phenols (hydroxytyrosol, tyrosol); secoiridoids (oleuropein, the aglycone of ligstroside, and their respective decarboxylated dialdehyde derivatives); and the lignans [(+)-1-acetoxypinoresinol and pinoresinol]. All three classes have potent antioxidant properties. High consumption of extra-virgin olive oils, which are particularly rich in these phenolic antioxidants (as well as squalene and oleic acid), should afford considerable protection against cancer (colon, breast, skin), coronary heart disease, and ageing by inhibiting oxidative stress.