ARTICLE
Auteur(s) : Joaquín J
Salas, Miguel A Bootello, Enrique Martínez-Force, Rafael
Garcés
Instituto de la Grasa, CSIC, Av. Padre García Tejero,
4, 41012, Sevilla, Spain
Introduction
Vegetable fats and oils are extracted from oil seeds and fruits and
are the main lipid source in a healthy human diet [1]. These fats
and oils consisted of triacylglycerols (TAGs), whose
characteristics depend on their fatty acid composition. Oils rich
in unsaturated fatty acids are usually liquid at room temperature,
whereas the presence of saturated fatty acids increases the melting
point of the fat or oil. In this regard, more than 75% of the world
vegetable lipid production consists of liquid oils, which are used
for retailing, frying, canning and preparation of emulsions or
margarines [2]. Furthermore, solid fats constitute less than 25% of
the world production of vegetable lipids and their applications are
eminently industrial because they are the raw material for the
production of structured lipids and confectionary fats that are the
base for a great variety of food products. The main sources of
solid vegetable fats are palm stearins, palm kernel oil, coconut
fat, cocoa butter and other butters coming from any other exotic
sources like shea, kokum, mango or illipe. A common factor of
all these solid fats and butters is that all they are of tropical
origin. The cause of this phenomenon is the close relationship
between the TAG synthesis metabolism and the pathways of
phospholipids synthesis. Thus, the esterification of the acyl
moieties to the glycerol backbone takes place through the Kennedy
pathway that involves successive acylation of glycerol-3-P to yield
finally a TAG molecule [3]. The main phospholipids present in plant
membranes came from ramifications of this pathway, therefore, TAG
and phospholipids display similar fatty acid compositions in a
given plant organ. On the other hand, biological membranes require
a certain degree of fluidity to be functional and this fluidity
depends on the degree of saturation of the fatty acids esterified
to membrane lipids and temperature [4]. High levels of saturated
fatty acids in membrane lipids are incompatible with low
temperatures, due to membranes would become brittle causing cell
lysis and death. Therefore, the accumulation of saturated fatty
acids in TAGs involve high levels of saturated fatty acids in
membrane lipids, which only can be supported by permanent high
temperatures of tropical climates.
Tropical fats and butters are solid or semisolid at room
temperature because they contain high levels of saturated fatty
acids in their TAGs. In this regard, they can be classified on the
basis of the predominant saturated fatty acid that they contain.
Therefore, there are three main groups of tropical vegetable fats:
those containing lauric, palmitic or stearic fatty acid. Fats
within each group display different properties and origins and are
usually fated to different uses.
Lauric fats
Lauric fats are those accumulating medium and short chain fatty
acids (mainly lauric and myristic) as the main fatty acid in their
oils. These fats come mainly from palm kernel and coconut, which
displays similar fatty acid composition in their reserve TAGs.
Thus, these fats contain around 50% lauric acid, between
15 and 20% myristic acid, and 8-15% of saturated shorter
chained fatty acids, which are usually more abundant in coconut fat
(table 1, [5]). Another characteristic
of these fats is the fatty acid distribution within the TAG
backbone. Saturated fatty acids are mainly excluded from the
sn-2 position of the TAG molecule in plants. This is not the
case of lauric fats, which accounts for high levels of lauric acid
in that position. Thus, table 1
indicated that the sn-2 position of coconut accumulated
important amounts of saturated fatty acids, above all lauric acid,
which was present in that position in amounts close to 80%. Other
saturated fatty acids were evenly distributed amongst the
sn-1 and sn-3 TAG positions.
These TAG compositions confer to lauric fats melting profiles
ranging from 10 to 30 °C that are not enough for the
elaboration of confectionary products. Thus, these fats are usually
fractionated to yield a stearin with a melting range around
30 °C, which is used in confectionary as cocoa butter
substitute and an olein that is hydrogenated to increase its
content of solids [6]. The versatility and the mouthful of lauric
fats make them an excellent base for a variety of food products
like chocolate substitutes (CBS), filling creams, toffees,
caramels, ice creams, milk products, cream substitutes and being a
source of saturated fatty acids for the production of structured
lipids and margarines [7]. However, on the negative side, there is
a clear scientific consensus about the atherogenic effects of
laurate and myristate. These fatty acids increase the levels of
blood plasma cholesterol and induce arteriosclerosis. Furthermore,
these effects on human health are enforced by the TAG structure
found in lauric fats, in which the high levels of saturated fatty
acids in sn-2 position assure a quick absorption and
incorporation of these fatty acids into human membrane lipids [8].
In the case of hydrogenated lauric oleins, the atherogenic effects
are even enhanced by the presence of trans fatty acids [9], so the
use of this kind of fats in confectionary should be restricted as
much as possible. Since they are not recommendable as food, the
future of lauric fats maybe relies on being a renewable feedstock
for soap and oleochemical industries.
Table 1 Typical fatty acid composition of palm kernel
and coconut oils. Distribution of fatty acids between the sn-2 and
sn-1, 3 positions of triacylglycerol in the case of coconut oil.
Data taken from reference [5].
|
Fatty acids (mol%)
|
|
C6-C10
|
12:0
|
14:0
|
16:0
|
18:0
|
18:1
|
18:2
|
|
Palm Kernel
|
8
|
48
|
16
|
8
|
2
|
15
|
3
|
|
Coconut
|
15.6
|
47.9
|
18.2
|
8.7
|
2.5
|
5.7
|
1.4
|
|
sn-2
|
4.1
|
78.2
|
10.2
|
-
|
-
|
5.9
|
2.0
|
|
sn-1+3
|
21.4
|
32.7
|
22.2
|
13.2
|
4.0
|
5.6
|
1.1
|
Fats rich in palmitic acid
The main source of vegetable fats rich in palmitic acid is palm
oil. Typically, palm oil is a semi solid fat with high content of
palmitic acid in a high oleic background, but still containing
important amounts of linoleic acid. The content of palmitic acid
ranged around 45 % of total composition with levels of oleic acid
close to 40% (table 2). The fatty acids
present in this oil are distributed in a broad variety of TAGs,
including trisaturated, disaturated and triunsaturated ones (table 2). This confers to palm oil a very
broad melting interval ranging from – 20 to 50 °C,
which makes it impractical for many uses (figure 1). Therefore, palm
oil is usually fractionated to obtain fractions with more specific
properties [10]. Palm oil fractionation is a complex process, with
multiple steps involving the enrichment of certain TAGs on the
basis of their different physical properties. Thus, olein liquid
fractions are enriched in monosaturated or triunsaturated TAGs and
they are liquid or semi liquid at room temperature (figure 1), being usually
fated to frying and retailing [11], stearins are enriched in
disaturated and trisaturated TAGs and are solid fractions (figure 1) used as
source of saturated fatty acids to harden oils in order to produce
structured fats [12]. Palm mid fractions (PMF) are enriched in
disaturated TAGs, and are extensively used to produce confectionary
fats [10]. The composition of palm oil and the versatility of the
fractionation process allow producing fats with a variety of
characteristics at very competitive prices, which are making palm
fractions to displace other oils from international market. In this
regard, palm oleins are more stable than most vegetable oils [13].
Palm stearins are widely used to prepare shortenings and
margarines. Shortenings are prepared by transesterification of palm
and palm kernel stearins with other oils, using often a step of
hydrogenation to increase the level of solids of the final fats
[12]. Margarines are produced by transesterification of palm
stearins with liquid oils. Depending on the final use they require
different melting profiles (table, pastry or cake margarines) and,
as in the case of shortenings, an extra step of hydrogenation could
be necessary to reach the desired melting curve. Palm mid fractions
display a steep melting profile (figure 1) that make them
useful to produce confectionary fats, being the source of palmitic
acid-rich disaturated TAGs in formulations of cocoa butter
equivalents (CBEs).
Palmitic acid increases the levels of blood plasma cholesterol
in a lower extent than C12-C14 fatty acids [8]. Moreover,
little saturated fatty acids are located in the sn-2 position
of TAGs from palm oil and oleins, which are also rich in oleic
acid. Thus, there is evidence showing that these oils are not as
atherogenic as previously supposed [14]. But many formulations with
palm oil involve concentration of the trisaturated TAGs, chemical
randomization, transesterification or hydrogenation, which really
increases negative effects on human health of the derivatives of
this oil [15, 16]. The increasing concern of consumers all around
the word on the impact of different fats on human health makes that
the main challenge of this area of food science is producing
healthy fats for food commodities by physical means, suppressing
hydrogenation.
Table 2 Fatty acid and main triacylglycerol composition
of palm oil. Data taken from reference [5].
|
Fatty acids (mol%)
|
|
12:0
|
14:0
|
16:0
|
16:1
|
18:0
|
18:1
|
18:2
|
18:3
|
|
Palm oil (malaysia)
|
0.2
|
1.1
|
44.1
|
0.2
|
4.4
|
39.0
|
10.6
|
0.3
|
|
Triacylglycerols (mol%)
|
|
TAGs
|
PPP
|
POP
|
POSt
|
POO
|
OOO
|
|
|
Others
|
|
5.4
|
29.0
|
5.1
|
22.8
|
4.3
|
|
|
33.4
|
Fats rich in stearic acid
Fats rich in stearic acid are usually referred as butters and the
more important tropical butter is that obtained from seeds of the
cocoa (Theobroma cacao) fruit. Cocoa butter (CB) is rich in
stearic, oleic and palmitic acids (table
3). This fat is quite rich in disaturated TAGs (85-90%),
containing very little saturated fatty acids in the
sn-2 position (table 3). Since
stearic acid does not exert a negative impact on human health,
stearic fats are not generally classified as atherogenic [17]. The
most important characteristic of CB is its steep melting curve,
which displays a narrow melting interval around 35 °C that
confers chocolate and other confectionary fats their typical
characteristics (figure
2, [18]). In this regard, CB quickly melts in mouth
releasing flavours and creating a refreshing sensation. This fat is
also characterized by a complex polymorphism, with six different
crystalline forms that give place to five isomorphs and a high
number of possible transitions [19]. Cocoa butter production is
hampered by its difficult cultivation, low productivity and pest
attacks. These facts, together with an increasing world demand,
create market tensions, so it would be necessary to find
alternatives. Amongst the classical alternatives to cocoa butter
are lauric fats or cocoa butter substitutes, already mentioned in
preceding sections, and hydrogenated oils or cocoa butter replacers
(CBR). Lauric CBS increase levels of human blood plasma cholesterol
and displays low compatibility when blended with CB, giving place
to eutectic mixtures. CBRs are more compatible with CB, but the
tendency of food industry is removing any source of trans-fatty
acids in their products. The third alternative are blends of palm
mid fractions with fats rich in stearic and oleic fatty acids that
can be obtained from certain tropical nuts and seeds like shea,
mango, kokum or illipe. These fats are called cocoa butter
equivalents (CBEs) and displays similar melting profiles than CB,
are fully compatible with it and they do not exert negative effects
on human health. Moreover, it is possible to alter the properties
of CBEs by manipulating the blending of stearic butters with the
added PMFs producing soft and hard CBEs as well as what is called
cocoa butter improvers (CBIs), which are butters with a higher
melting point that help to keep CB properties in warm climates.
Table 3 Fatty acid and main triacylglycerol composition
of coconut oil from different world locations. Data taken from
reference [5].
|
Ghana
|
Coast
|
Brazil
|
Malaysia
|
|
Fatty acids (mol%)
|
|
Palmitic
|
24.8
|
25.4
|
23.7
|
24.8
|
|
Stearic
|
37.1
|
35.0
|
32.9
|
37.1
|
|
Oleic
|
33.1
|
34.1
|
37.4
|
33.2
|
|
Linoleic
|
2.6
|
3.3
|
4.0
|
2.6
|
|
Palmitic
|
24.8
|
25.4
|
23.7
|
24.8
|
|
Triacylglycerols (mol%)
|
|
Trisaturated
|
0.7
|
0.6
|
trace
|
1.3
|
|
Monounsaturated
|
84.0
|
82.6
|
71.9
|
87.5
|
|
Diunsaturated
|
14.0
|
15.5
|
24.1
|
10.9
|
|
Polyunsaturated
|
1.3
|
1.3
|
4.0
|
0.3
|
|
POP
|
15.3
|
15.2
|
13.6
|
15.1
|
|
POSt
|
40.1
|
39.0
|
33.7
|
40.4
|
|
StOSt
|
27.5
|
27.1
|
23.8
|
31.0
|
New alternatives to tropical fats
The uneven distribution of the production of solid fats against
liquid oils made that the search for alternatives to tropical solid
fats and butters had been an important target of oil industry in
the last decades. As it has been depicted above, increasing the
melting point of liquid oils by hydrogenation has been the choice
of industry for a long time. However, the important concern about
the negative effects of trans-fat on human health has made that
important health organizations recommended the total removal of
these fatty acids from diet [16]. Another alternative to increase
the degree of saturation of liquid oils is by the means of
transesterification with a saturated fat. This technique is
extensively used to produce structured lipids and usually involves
the exchange of the acyl moieties by using a chemical catalyser
followed of fractionation of the resulting TAGs. This operation
usually implies the increment of the saturated fatty acid content
in the sn-2 position of the fat product, which in common
vegetable oils is usually occupied by an unsaturated one.
Increasing the content of saturated fatty acids in the
sn-2 position increments its absorption in intestine and
enables their thorough incorporation into human lipids, negatively
affecting cardiovascular health [15]. Nevertheless, new
alternatives to tropical fats should be easily accessible, cost
effective and compatible with a healthy diet to improve the present
status quo. In this regard, advances on biological sciences and the
understanding of pathways of lipid synthesis has revealed lipid
biotechnology as an useful tool to provide with new fats and oils
that could compete with those traditionally coming from tropical
climates. The pathways and enzymes involved in plant oil synthesis
were described trough the 80’s and 90’s decades. Since then, one of
the main targets of plant lipid biotechnology has been producing
oils enriched in saturated fatty acids in common annual oil crops
to cover the growing demand for them [20]. Genetic engineering and
mutagenesis techniques allow modifying the TAG composition of oils
from many oil crops.
High laurate Canola
The breakout of biotechnology in the field of tropical fats was
quick and very promising. At the beginning of the 90’s Calgene
produced lines of canola expressing a thioesterase from
Umbellularia californica, which was able to redirect the fatty acid
biosynthetic pathway, inducing the accumulation of lauric acid in
the oil [21]. Fatty acids are synthesized in the chloroplast or
plastids of plant cells in a process involving successive
elongations of an acyl-ACP derivative by the action of the fatty
acid synthetase. These reactions are terminated by acyl-ACP
thioesterases, which are enzymes that hydrolyze acyl-ACP complexes.
The fatty acids released are transported to the cytosol in the form
of acyl-CoAs and incorporated into TAGs. The expression of a
thioesterase from Umbellularia californica in canola seeds ramifies
the regular pathway of fatty acid synthesis inducing accumulation
of lauric acid in the oil at levels as high as 40%. This oil was
commercialized as Laurical and its content of lauric acid and its
distribution in the TAG molecule was improved by the introduction
of new genes and promoters. This oil was used for the production of
soap and surfactants; however, it has not significantly altered the
world market of lauric fats, probably because the world demand of
these fats is well covered by the current production of coconut and
palm kernel.
High palmitic oils
The great demand of palmitic fats for structured lipid production
activated projects for increasing the levels of this fatty acid in
common oil crops during the last decade. The enrichment of palmitic
acid in non-tropical oil crops is possible by suppressing or
reducing β-ketoacyl-ACP synthase II activity. This is the enzyme
catalyzing the last plastidic elongation that takes place in plant
fatty acid synthesis, converting 16:0-ACP into 18:0-ACP, which is
then desaturated in a great extension by the enzyme stearoyl-ACP
desaturase, SAD, and exported to the cell cytosol in the form of
oleoyl-CoA. The blockage of this metabolic step by techniques of
RNA interaction (hairpin or antisense RNA expression) or gene
mutagenesis have been successful at producing oils with increased
levels of palmitic acid. These levels ranged 25 to 35% (table 4) in sunflower [22], soybean [23],
canola [24] and linseed [25], but none of them reached more than
40%, which would be closer to the composition of palm oil. The
cause of this was probably that the enzymes involved TAG synthesis
in common oil crops are not able to esterify saturated acyl
moieties in the sn-2 position of these molecules. On the other
hand, soybean, rape or sunflower oils are rich in linoleic acid,
therefore it would be necessary to reduce the levels of this fatty
acid at expenses of oleic to better mimic the palm oil composition.
This can be fulfilled by blocking the oleic acid desaturation.
Unlike fatty acid synthesis oleic acid desaturation occurs out of
the plastid, through an ER-located desaturase that acts on oleate
bound to the sn-2 position of phosphatidyl-choline, which is
called FAD2. The blockage of FAD2 by different means (RNA
interaction or mutagenesis) has been achieved in many oil crops,
and it could be combined with the high palmitic trait to produce
lines such as sunflower CAS-12 combining contents of palmitic
acid around 30% in a high oleic background, containing linoleic
acid levels lower than those in palm oil [22]. Although these oils
could be a good source of palmitic fats for food industry none of
them is currently under exploitation. The reason for this is the
great boost of oil palm production that has took place in the
Southeast Asia the last years. Thus, palm oil is more abundant and
cheap than oil crops growing in temperate climates. Moreover, it
displays higher contents of saturates than the above depicted
mutants lines, which makes that they did not represent an
attractive alternative in this moment.
Table 4 Fatty acid composition of different oil crops
engineered for the production of palmitic acid.
|
Fatty acids (mol%)
|
|
16:0
|
16:1
|
18:0
|
18:1
|
18:2
|
18:3
|
20:0
|
22:0
|
|
Soybean [23]
|
30.4
|
-
|
5.2
|
10.1
|
42.6
|
11.7
|
-
|
-
|
|
Canola [24]
|
27.0
|
1.2
|
2.8
|
28.8
|
23.2
|
14.0
|
2.0
|
1.0
|
|
Sunflower [22]
|
30.7
|
7.6
|
2.1
|
56.0
|
3.1
|
-
|
-
|
-
|
|
Linseed [25]
|
28.4
|
4.0
|
3.8
|
13.5
|
6.3
|
43.0
|
-
|
-
|
Oils enriched in stearic acid
Increasing the content of stearic acid in common oil crops involves
the blockage of the step of desaturation of acyl-ACP catalyzed by
the enzyme SAD. Equally to the above mentioned oils enriched in
palmitic acid, this can be carried out by techniques of genetic
engineering (hairpin or antisense RNA technologies) or by
mutagenesis of seeds. Decreasing SAD levels during seed development
leads to important increases of stearic acid in the seed oil. This
has been achieved in several crops like soybean [26], canola [27],
cotton seed [28] and sunflower [29]. Moreover, these high stearic
phenotypes should be expressed on high oleic backgrounds to mimic
better the composition of tropical fats rich in this fatty acid.
Therefore, SAD decrease should be combined with the blockage of
FAD2 enzyme to yield lines with high stearic-high oleic
content in their oils. The stearic acid oil content in the oil of
these species was increased from initial 3-6% to 20-40% in the
mutated or engineered lines (table 5),
with contents of oleic acid ranging from 40 to 65% of total
fatty acids. Although the increment in stearic acid reached in
these mutant lines was really important, they are not still in the
range of the tropical species used as the source of
stearic-oleic-stearic (StOSt) TAG for the preparation of
confectionary fats, and further increments of total saturated fatty
acid content is hampered by the enzymatic machinery in these
species, which sometimes is not specific for the accumulation of
disaturated TAGs. Furthermore, in the case of “green” seeds, like
canola or soybean, a certain content of linolenic acid is always
found in the oil (1-3%), this fatty acid is not desirable in
confectionary fats because its low melting point and unstability.
Other problems reported in oilseed crops enriched in stearic acid
referred to seed germination, thus very high levels of this fatty
acid have been reported to decrease considerably the rates of
germination in antisense mutants from canola plants [27].
High stearic-high oleic oils presents lower saturated fatty acid
content than CB, which makes that their melting profiles are far
from that found in the butter of that specie (figure 2). However, this
have not been an impediment for a growing interest in these oils.
Thus, StOSt-rich butters are usually produced from tropical nuts
that do not ensure a reliable supply. The levels of saturated fatty
acids in the new engineered oils could be increased by techniques
of dry or solvent fractionation already applied for other tropical
fats like palm, coconut and palm kernel oils. Dry fractionation
involves crystallization of the oil at low temperature in absence
of any solvent, followed of filtration at high pressure, which
allows expelling the liquid olein and enriches the solid fraction
in disaturated species of TAGs. In the case of solvent
fractionation the oil is dissolved in an organic solvent like
acetone or hexane. This micelle is cooled down and the resulting
stearin is filtered and washed with fresh solvent. The first type
of fractionation is often less efficient but lest costly than the
second one. In this regard, high stearic-high oleic sunflower oils,
which are being commercialized as healthy stable fats for frying,
are especially promising as a starting material for
fractionation.
Biotechnology also provides another way to produce StOSt. This
is transferring stearic acid to the sn-1, 3 positions of high
oleic oils through enzymatic transesterification. The source of
stearic acid would be tallow or fully hydrogenated oils chemically
hydrolyzed. These fatty acids can be esterified into the
sn-1 or sn-3 positions of high oleic oils by the action
of specific lipase enzymes, giving place to StOSt that could be
afterwards purified by fractionation [30]. Lipases from different
microorganism are available in market; ie. Lipozyme (Rhizomucor
Miehei) and lipases from Aspegillus Niger, Pseudomonas cpacia and
Penicillium camembertii. These enzymes can be immobilized for cost
optimization and allowed the scaling up of the process for
industrial production. This method also suffers of some drawbacks,
like cost optimization and European laws, which does not allow the
use of the TAGs produced in this way for CBE production.
Table 5 Fatty acid composition of different oil crops
engineered for the production of stearic acid.
|
Fatty acids (mol%)
|
|
16: 0
|
18:0
|
18:1
|
18:2
|
18:3
|
20:0
|
22:0
|
others
|
|
Cottonseed [28]
|
13.7
|
39.9
|
37.4
|
6.0
|
0.6
|
2.4
|
-
|
-
|
|
Sunflower [29]
|
5.4
|
20.4
|
66.3
|
3.3
|
-
|
1.7
|
2.8
|
-
|
|
Canola [27]
|
7.4
|
19.2
|
62.1
|
4.3
|
1.1
|
3.1
|
0.9
|
1.9
|
|
Soybean [26]
|
6.0
|
24.0
|
63.0
|
2.0
|
3.0
|
-
|
-
|
-
|
Acknoledgements
This work was supported by Advanta Seeds, MICINN and FEDER project
AGL 2008-01086/ALI.
References
1 Flickinger BD, Huth PJ. Dietary fats and oils:
technologies for improving cardiovascular health. Curr Atheroscler
Rep 2004 ; 6 : 468-76.
2 Gunstone FD. Vegetable Oils in Food Technology. Boca
Raton, Florida, USA : CRC Press, 2002.
3 Ohlrogge J, Browse J. Lipid biosynthesis. Plant Cell
1995 ; 7 : 957-70.
4 Falcone DL, Ogas JP, Somerville CR. Regulation
of membrane fatty acid composition by temperature in mutants of
Arabidopsis with alterations in membrane lipid composition. BMC
Plant Biol 2004 ; 4 : 17.
5 Gunstone FD, Harwood JL, Dijkstra DJ. The lipid
handbook. Boca Raton, Florida, USA : CRC Press, 2007.
6 Siew WL. Crystallisation and melting behaviour of palm
kernel oil and related products by differential scanning
calorimetry. Eur J Lipid Sci Technol 2001 ; 103 :
729-34.
7 Pantzaris TP, Mohd JA. Properties and utilization of
palm kernel oil. Palm Oil Developments 2001 ; 35 :
11-23.
8 Katan MB, Zock PL. Mensink. Dietary oils, serum
lipoproteins, and coronary heart disease. Am J Clin Nutr
1995 ; 61 : 1368S-1373S.
9 De Roos N, Schouten E, Katan M. Consumption of
a solid fat rich in lauric acid results in a more favourable serum
lipid profile in healthy men and women than consumption of a solid
fat rich in trans-fatty acids. J Nutr 2001 ; 131 :
242-5.
10 Kellens MJ. Oil modification processes. In :
Hamm W, Hamilton RJ, eds. Edible oil processing.
Sheffield, UK : Academic Press, 2001 : 129-73.
11 Matthäus B. Use of palm oil for frying in comparison
with other high-stability oils. Eur J Lipid Sci Technol 2007 ;
109 : 400-9.
12 Aini IN, Miskandar MS. Utilization of palm oil and
palm products in shortenings and margarines. Eur J Lipid Sci
Technol 2007 ; 109 : 422-32.
13 Ismail R. Palm oil and palm olein frying applications.
Asia Pacific J Clin Nutr 2005 ; 14 : 414-9.
14 Ebong PE, Owu DU, Isong EU. Links Influence of
palm oil (Elaesis guineensis) on health. Plant Foods Hum Nutr
1999 ; 53 : 209-22.
15 Bell SJ, Bradley D, Forse RA,
Bistrian BR. The new dietary fats in health and disease. J Am
Diet Assoc 1997 ; 97 : 280-6.
16 Zaloga GP, Harvey KA, Stillwell W,
Siddiqui R. Trans fatty acids and coronary heart disease. Nutr
Clin Pract 2006 ; 21 : 505-12.
17 Elson CE. Tropical oils: nutritional and scientific.
Crit Rev Food Sci Nutr 1992 ; 31 : 79-102.
18 Shukla VKS. Cocoa butter properties and quality. Lipid
Technol 1995May: 54-7.
19 Smith KW. Cocoa butter and cocoa butter equivalents.
In : Gunstone FD, ed. Structured and modified lipids. New
York : Marcel Dekker, 2001 : 401-22.
20 Drexler H, Spiekermann P, Meyer A, et al.
Metabolic engineering of fatty acids for breeding of new oilseed
crops: strategies, problems and first results. J Plant Physiol
2003 ; 160 : 779-802.
21 Voelker TA, Worrell AC, Anderson L,
et al. Fatty acid biosynthesis redirected to medium chains in
transgenic oilseed plants. Science 1992 ; 257 : 72-4.
22 Fernández-Martínez JM, Mancha M, Osorio J,
Garcés R. Sunflower mutant containing high levels of palmitic
acid in high oleic background. Euphytica 1997 ; 97 :
113-6.
23 Fehr WR. Inheritance of elevated palmitic acid content
in soybean seed oil. Crop Sci 1991 ; 31 : 1522-4.
24 Jones A, Davies HM, Voelker TA. Palmitoyl-acyl
carrier protein (ACP) thioesterase and the evolutionary origin of
plant acyl-ACP thioesterases. Plant Cell 1995 ; 7 :
359-71.
25 Rowland GG, Bhatty RS. Ethyl methanesulfonate
induced fatty acid mutations in flax. JAOCS 1990 ; 67 :
213-4.
26 Knowlton S. Fat products from high stearic soybean oil and a
method for the production thereof. WO/1999/057990. 1999.
27 Knutzon DS, Thompson GA, Radke SE,
Johnson WB, Knauf VC, Kridl JC. Modification of
Brassica seed oil by antisense expression of a stearoyl-acyl
carrier protein desaturase gene. Proc Nat Acad Sci USA 1992 ;
89 : 2624-8.
28 Liu Q, Singh SP, Green AG. High-Stearic and
High-Oleic Cottonseed Oils Produced by Hairpin RNA-Mediated
Post-Transcriptional Gene Silencing. Plant Phys 2002 ;
129 : 1732-43.
29 Pleite R, Martinez-Force E, Garces R. Increase
of the stearic acid content in high-oleic sunflower (Helianthus
annuus) seeds. J Agric Food Chem 2006 ; 54 : 9383-8.
30 Seriburi V, Akoh CC. Enzymatic transesterification
of triolein and stearic acid and solid fat content of their
products. JAOCS 1998 ; 75 : 511-6.
|
Version imprimable
Version PDF
