Caballero B. (ed.) Encyclopaedia of Food Science, Food Technology and Nutrition. Ten-Volume Set
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Oil sample
TLC
Pancreatic lipase
TLC FAME GLC
TG 2-MG
Hydrolysis
FAME
GLC
Grignard degradation 2
+
1
11
TLC
1
2
+
2
+
+
+
2
+
OR
3
3
33
TLC
Silica gel/H
3
BO
3
(S)-(+)-(1-Naphthyl)Ethyl isocyanate
3,5-DNP
Isocyanate
3,5-DNP
Isocyanate
sn-1,2 DG +sn-2,3 DG
3,5-DNP Isocyanate
sn-1,2 DG 3,5-DNPU
sn-1,2 DG Urethane
sn-2,3 DG 3,5-DNPU
sn-2,3 DG Urethane
Synthesis
sn-1,2-DG Kinase
phosphorylation
TLC ODS SPE
sn-1-MG 3,5-DNPU
1
sn-3-MG 3,5-DNPU
22
HPLC
CHIRAL
COLUMN
HPLC
CHIRAL
COLUMN
PC
PC
3
TLC
HPLC
SILICA
GEL
COLUMN
L- and D-phosphatidylcholines
1
Phospholipase A
FAMEFAMEFAMEFAME
PC
3
+ 2
+ 2
GLCGLCGLCGLC
PC
Lysophosphatide
FAME
FAME
GLC
GLC
Method B
Lands et al.
(1966)
Method C
Itabashi et al. (1990)/
Myher et al. (1996)
Method D
Laakso et al. (1990)
Christie et al. (1991)
Method E
Takagi & Ando
(1991, 1995)
Method A
Modified Brockerhoff
Figure 2 Basic features of the methods used in the determination of the fatty acid distribution between the sn-1, sn-2, and sn-3 positions in triacyl-sn-glycerols. TLC, thin-layer
chromatography; GLC, gas–liquid chromatography; HPLC, high-performance liquid chromatography; TG, triacylglycerol; 2-MG, 2-monoglyceride; FAME, fatty acid methyl ester.
fig0002
3,5-dinitrophenyl urethanes of 1,2- and 2,3-diacyl-
sn-glycerols and 1- and 3-monoacyl-sn-glycerols,
respectively. The method D (Figure 2) is based on
the separation of diastereomeric derivatives of 1,2-
and 2,3-diacyl-sn-glycerols on a silica-gel HPLC
column.
Triacylglycerol Structure of Food Fats and
Oils
Fruit Pulp Oils
0003 In olive oil, the saturated fatty acids are esterified
mainly in the sn-1 and sn-3 positions (Table 1). A
little more than one-third of oleic acid is esterified in
the sn-2 position and a little less in the sn-1 and sn-3
positions. The ratio of both primary positions is close
to 1. Nearly half of linoleic acid is esterified in the
sn-2 position and approximately one-third in the sn-
1 position. Table 1 shows a high degree of similarity
between the distributions determined by two enzym-
atic methods. A study by Damiani et al. did not reveal
any statistical difference between the methods B and
D(Figure 2) by Student’s t-test. Also, in palm oil,
saturated fatty acids are preferentially esterified in
the sn-1 or sn-3 positions. Unsaturated fatty acids
are esterified to a great extent in the sn-2 position.
High Lauric and Myristic Acid Seed Oils
0004Regiospecific analysis has shown that in coconut
oil, lauric and linoleic acids are esterified mainly in
the sn-2 position and oleic acid and saturated acids
in the sn-1(3) positions (Table 2). A similar trend
is in the distribution of lauric and oleic acids in palm
kernel oil. Also, linoleic acid shows a slight preference
tbl0001 Table 1 Distribution of fatty acids between the sn-1, sn-2, and sn-3 positions in vegetable/fruit oil triacylglycerols
Fattyacid Total (mol%) Percentage Total (mol%) Percentage
sn-1 sn-2 sn-3 sn-1 sn-2 sn-3
Olive oil Palm oil
d
14:0 1.3 10.3 15.4 74.4
16:0 10.5 41.7 4.5 53.8 48.4 41.4 9.2 49.5
16:1 0.8 37.5 29.2 33.3 0.2 0.0 83.3 16.7
18:0 2.3 38.2 0.0 61.8 3.7 30.4 1.8 67.9
18:1 76.2 31.4 36.3 32.3 36.4 24.6 62.2 13.2
18:2 9.6 33.9 48.4 17.6 10.0 31.0 58.3 10.7
18:3 0.9 22.2 29.6 48.1
Olive oil
b
Olive oil
c
16:0 12.0 46.4 1.4 52.2 12.0 41.1 3.9 55.0
16:1 0.7 33.3 23.8 42.9 0.7 52.4 4.8 42.9
18:0 2.0 40.0 0.0 60.0 2.0 30.0 10.0 60.0
18:1 78.9 30.9 37.9 31.2 78.9 31.9 37.4 30.7
18:2 6.3 39.2 49.7 11.1 6.3 34.4 51.3 14.3
a
Enzymatic stereospecific analysis. Adapted from Brockerhoff and Yurkowski (1966).
b
Enzymatic stereospecific analysis using sn-1,2-diacylglycerol kinase. Adapted from Damiani et al. (1994).
c
Method based on separation of diastereomeric derivatives of diacylglycerols by silica gel HPLC. Adapted from Damiani et al. (1994).
d
Method based on separation of diastereomeric derivatives of diacylglycerols by silica-gel HPLC. Adapted from Christie et al. (1991).
tbl0002 Table 2 Distribution of fatty acids between the sn-1(3) and sn-2 positions in high lauric and myristic acid seed oil triacylglycerols
Fattyacid Total (mol%) Percentage Total (mol%) Percentage
sn-1(3) sn-2 sn-1(3) sn-2
Coconut oil
a
Palm kernel oil
a
6:0 0.6 50.0 0.0 0.4 50.0 0.0
8:0 9.4 49.5 1.1 5.7 42.1 15.8
10:0 7.0 42.9 14.3 4.7 41.1 17.7
12:0 50.0 23.2 53.6 52.8 30.2 39.6
14:0 17.4 41.8 16.5 16.2 33.7 32.5
16:0 7.6 46.5 7.0 7.6 43.6 12.7
18:0 2.0 45.0 10.0 2.2 47.7 4.5
18:1 4.7 37.6 24.8 9.2 28.6 42.8
18:2 1.2 29.2 41.7 1.2 31.9 36.1
a
Regiospecific analysis using pancreas lipase. Adapted from Mattson and Volpenheim (1963).
TRIGLYCERIDES/Structures and Properties 5859
for the sn-2 position. Myristic acid is distributed
equally between the sn-2 and sn-1(3) positions,
whereas the rest of saturated fatty acids are esterified
principally in the primary positions.
High Palmitic Acid Seed Oils
0005 In cocoa butter, palmitic and stearic acids are esteri-
fied to a great extent in the sn-1 and sn-3 positions,
distributing nearly equally between them (Table 3).
Arachidic acid is esterified totally in the sn-1 and sn-3
positions, the sn-3 position being more favored. Oleic
and linoleic acids are esterified mainly in the sn-2
position, and palmito-oleic acid in all three positions.
The distributions determined by enzymatic stereospe-
cific analysis and by chiral phase HPLC separation
of enantiomers of monoacylglycerol derivatives
(method E, Figure 2) were very similar. In maize oil,
palmitic and stearic acids are principally in the sn-1
and sn-3 positions (Table 3). Oleic acid is distributed
quite evenly between the three positions with a slight
excess in the sn-3 position. Linoleic acid is esterified
predominantly in the sn-2 position.
High Oleic and Linoleic Acid Seed Oils
0006 In soy bean oil, high-erucic acid rape seed oil, sun-
flower oil, and peanut oil, palmitic, and stearic acids
are esterified preferentially in the primary positions
(Table 4). Also arachidic, behenic, and lingnoceric
acids are esterified mainly in the primary positions,
the sn-3 position clearly being preferred in peanut oil.
Oleic acid (18:1n-9) is relatively evenly distributed
between the three positions in soy bean oil, sunflower
oil, and peanut oil, but is predominantly at the sn-2
position in high-erucic rape seed oil. Vaccenic acid
(18:1n-7) is esterified preferentially in the primary
positions in soy bean oil and high-erucic rape seed
oil. Eicosenoic and docosenoic acids are in the pri-
mary positions in high-erucic rape seed oil and peanut
oil. In sunflower oil, linoleic acid is esterified in all
positions, with a slight excess in the sn-2 position. In
soy bean oil, high-erucic rape seed oil, and peanut oil,
linoleic acid is preferentially in the sn-2 position.
Linolenic acid is esterified preferentially in the sn-2
position in high-erucic rape seed oil and relatively
evenly in all positions in soy bean oil. The distribu-
tions of soy bean oil fatty acids, determined by en-
zymatic stereospecific analysis and by HPLC
separation of monoacylglycerol derivatives on a
chiral column (method E, Figure 2), show a high
degree of accordance. Harp and Hammond applied
the method of Takagi and Ando in the stereospecific
analysis of soy bean mutants representing a wide
distribution of fatty acid compositions. In low-
erucic-acid rape seed oil, the sn-2 position has
reported to be occupied by unsaturated C18 fatty
acids in the order of linoleic > linolenic > oleic acids.
Milk Fat
0007Even-numbered triacylglycerols with 26–54 acyl
carbons dominate the triacylglycerol composition of
bovine milk fat, but odd-numbered triacylglycerols
are also present. Only very few triacylglycerols with
more than 54 or fewer than 26 acyl carbons exist,
indicating a scarcity of the molecular species with
very-long-chain fatty acids (> 20) or those with two
short-chain fatty acids, respectively. A high number
of mono-butyryl triacylglycerols is unique among
food fats.
tbl0003 Table 3 Distribution of fatty acids between the sn-1, sn-2, and sn-3 positions in high palmitic acid seed oil triacylglycerols
Fattyacid Total (mol%) Percentage Total (mol%) Percentage
sn-1 sn-2 sn-3 sn-1 sn-2 sn-3
Cocoa butter
a
Cocoa butter
b
16:0 24.1 47.1 2.4 50.6 26.5 46.4 3.1 50.5
16:1 0.4 54.5 18.2 27.3 0.2 28.6 28.6 42.9
18:0 35.1 47.9 2.0 50.1 35.7 49.3 1.8 48.9
18:1 36.1 11.4 80.7 7.9 33.5 9.1 87.1 3.9
18:2 3.4 12.6 83.5 3.9 2.9 8.0 85.1 6.9
18:3 0.1 0.0 100.0 0.0
20:0 1.1 30.3 0.0 69.7 1.0 12.9 0.0 87.1
Maize oil
a
16:0 11.2 53.1 6.8 40.1
16:1 0.2 60.0 20.0 20.0
18:0 2.1 51.6 3.2 45.2
18:1 28.2 32.5 31.3 36.2
18:2 57.2 29.0 40.9 30.1
18:3 1.0 41.4 24.1 34.5
a
Enzymatic stereospecific analysis. Adapted from Brockerhoff and Yurkowski (1966).
b
Method based on separation of enantiomers of monoacylglycerol derivatives by chiral-phase HPLC. Adapted from Takagi and Ando (1995).
5860 TRIGLYCERIDES/Structures and Properties
0008 The asymmetric distribution of fatty acids in
bovine milk fat between the three sn-positions has
already been demonstrated in the late 1960s by Pitas
et al. and by Breckenridge and Kuksis. Short-chain
fatty acids (4:0, 6:0) in mono-butyryl and mono-
caproyl triacylglycerols are almost exclusively in the
sn-3 position (Table 5). However, a small amount of
triacylglycerols with two short-chain acyl groups has
been detected, and thus traces of butyric and caproic
acids have to be esterified in the sn-1 and/or sn-2
positions. Medium-chain fatty acids (8:0, 10:0) are
also most prominently in the sn-3 position. More
than 50% of lauric and myristic acids is esterified in
the secondary position in triacylglycerols. Fatty acids
tbl0004 Table 4 Distribution of fatty acids between the sn-1, sn-2, and sn-3 positions in high oleic and linoleic acid seed oil triacylglycerols
Fatty acid Total (mol%) Percentage Fatty acid Total (mol%) Percentage
sn-1 sn-2 sn-3 sn-1 sn-2 sn-3
Soy bean oil
a
Soy bean oil
b
14:0 0.1 75.0 75.0 50.0 14:0 0.1 33.3 33.3 33.3
16:0 11.6 48.4 4.0 47.6 16:0 11.7 47.7 6.3 46.0
16:1 0.1 50.0 50.0 0.0 16:1 0.1 33.3 33.3 33.3
17:0 0.0 100.0 0.0 0.0 17:0 0.1 50.0 0.0 50.0
18:0 3.4 51.0 2.9 46.1 18:0 3.4 52.4 2.9 44.7
18:1n-9 24.1 29.9 33.2 36.9 18:1n-9 22.7 32.6 33.8 33.6
18:1n-7 1.4 47.6 9.5 42.9 18:1n-7 1.4 50.0 9.5 40.5
18:2 53.9 29.3 42.8 27.9 18:2 53.8 28.7 42.2 29.1
18:3 6.4 39.3 29.8 30.9 18:3 6.4 33.5 29.8 36.6
20:0 0.3 22.2 0.0 77.8 20:0 0.3 55.6 0.0 44.4
Rape seed oil (high erucic acid)
c
Rape seed oil (high erucic acid)
b
14:0 0.1 25.0 50.0 25.0
16:0 3.0 45.6 6.7 47.8 16:0 3.9 47.9 13.7 38.5
16:1 0.3 37.5 25.0 37.5 16:1n-9 0.1 0.0 14.3 85.7
16:1n-7 0.3 37.5 37.5 25.0
17:1n-8 0.1 0.0 100.0 0.0
18:0 1.7 42.3 0.0 57.7 18:0 1.3 47.5 10.0 42.5
18:1 25.7 30.0 48.4 21.6 18:1n-9 17.2 26.8 63.3 10.0
18:1n-7 1.4 65.1 23.3 11.6
18:2 17.1 21.7 70.5 7.8 18:2n-6 16.1 2.5 82.0 15.4
18:3 9.8 21.8 69.3 8.9 18:3n-3 8.7 12.7 82.2 5.0
20:0 0.0 20:0 0.8 47.1 35.3 17.6
20:1 11.9 45.9 5.6 48.5 20:1n-9 8.9 57.4 5.6 37.0
20:1n-7 1.5 44.2 9.3 46.5
20:2n-6 0.5 80.0 6.7 13.3
22:0 0.9 53.8 0.0 46.2 22:0 0.7 0.0 0.0 100.0
22:1 29.8 39.0 4.0 57.0 22:1n-9 37.4 44.7 0.7 54.6
22:1n-7 0.6 47.4 0.0 52.6
22:2n-6 0.5 56.3 0.0 43.8
Sunflower oil
d
16:0 7.2 49.1 6.0 44.9
18:0 4.6 24.3 8.1 67.6
18:1 21.9 25.3 32.7 42.0
18:2 66.3 34.9 38.2 26.9
Peanut oil
c
Peanut oil
e
16:0 8.7 51.9 6.1 42.0 16:0 11.6 57.0 6.3 36.7
16:1 0.2 42.9 14.3 42.9 16:1 0.1 18.2 21.2 60.6
18:0 3.3 46.0 3.0 51.0 18:0 2.8 42.7 12.2 45.1
18:1 58.3 33.8 33.4 32.7 18:1 50.8 31.2 33.4 35.5
18:2 22.4 27.6 57.5 14.9 18:2 27.8 30.5 56.3 13.2
20:0 1.6 14.9 0.0 85.1 20:0 1.4 7.0 0.0 93.0
20:1 1.4 26.8 7.3 65.9 20:1 1.4 19.4 0.0 80.6
22:0 2.4 17.8 4.1 78.1 22:0 2.6 1.3 1.3 97.3
24:0 1.3 17.5 12.5 70.0 24:0 1.1 0.0 0.0 100.0
a
Enzymatic stereospecific analysis using modified Brockerhoff method. Adapted from Takagi and Ando (1991).
b
Method based on separation of enantiomers of monoacylglycerol derivatives on a chiral HPLC column. Adapted from Takagi and Ando (1991).
c
Enzymatic stereospecific analysis. Adapted from Brockerhoff and Yurkowski (1966).
d
Method based on separation of diastereomers of diacylglycerol derivatives on a silica-gel HPLC column. Adapted from Christie et al. (1991).
e
Enzymatic stereospecific analysis using Brockerhoff method. Adapted from Myher et al. (1978).
TRIGLYCERIDES/Structures and Properties 5861
tbl0005 Table 5 Distribution of fatty acids between the sn-1, sn-2, and sn-3 positions in mammals’ milk triacylglycerols
Fattyacid Total (mol%) Percentage Total (mol%) Percentage
sn-1 sn-2 sn-3 sn-1 sn-2 sn-3
Bovine milk fat
a
Human milk fat
a
4:0 11.8 100.0
6:0 4.6 6.5 93.5
8:0 1.9 24.5 12.3 63.2
10:0 3.7 17.1 27.0 55.9 2.9 12.8 18.6 68.6
12:0 3.9 41.9 53.0 5.1 7.3 20.6 31.7 47.7
14:0 11.2 28.9 52.1 19.0 9.4 23.0 54.4 22.6
15:0 2.1 31.7 46.0 22.2 0.8 24.0 36.0 40.0
16:0 23.9 47.4 45.1 7.5 27.0 23.1 70.4 6.5
16:1 2.6 35.9 46.1 18.0 3.6 31.5 14.8 53.7
17:0 0.8 54.1 41.7 4.2
18:0 7.0 49.1 45.2 5.7 7.1 66.7 23.0 10.3
18:1 24.0 41.7 26.2 32.1 34.2 42.9 7.9 49.2
18:2 2.5 22.7 46.6 30.7 7.9 30.5 15.7 53.8
18:3 tr. tr.
Goat milk fat
b
Sheep milk fat
b
4:0 4.4 100.0 3.6 100.0
6:0 3.5 100.0 3.5 100.0
8:0 2.5 22.7 16.0 61.3 2.2 4.5 29.8 65.7
10:0 7.5 14.7 30.8 54.5 5.6 8.3 30.8 60.9
10:1 0.2 16.7 83.3 0.2 20.0 80.0
12:0 3.3 40.8 47.0 12.2 3.5 21.2 45.2 33.6
14:0 10.4 26.7 64.7 8.6 10.4 26.4 56.9 17.0
14:1 0.6 44.4 55.6 0.7 9.1 40.9 50.0
15:0 2.0 31.1 44.3 24.6 2.7 31.7 50.0 18.3
16:0 26.9 53.9 41.9 4.2 21.5 59.1 37.0 3.9
16:1 2.2 44.6 30.8 24.6 2.0 37.3 37.3 25.4
17:0 1.2 36.1 13.9 50.0 1.1 51.5 27.3 21.2
18:0 9.8 52.2 21.5 26.3 13.6 46.8 30.9 22.3
18:1 20.8 25.8 25.8 48.4 21.8 28.7 29.6 41.7
18:2 2.4 4.1 34.3 61.6 4.3 20.9 32.6 46.5
18:3 2.8 26.5 20.5 53.0
20:1 1.8 17.0 32.1 50.9 0.4 45.4 18.2 36.4
20:2 0.5 28.6 7.1 64.3 0.1 100.0
Horses’ milk fat
c
Pigs’ milk fat
c
4:0
6:0 0.3 100.0
8:0 2.3 2.9 44.1 53.0
10:0 3.6 6.5 42.6 50.9
12:0 4.3 23.1 48.4 28.5 0.1 50.0 100.0 50.0
14:0 5.0 34.2 60.4 5.4 2.4 24.7 69.8 5.5
14:1 0.9 40.7 40.7 18.6
15:0 0.3 54.6 63.6 18.2 0.2 50.0 83.3 33.3
15:1 0.2 40.0 40.0 20.0
16:0 16.4 47.9 51.7 0.4 26.9 32.6 59.6 7.7
16:1 9.0 31.2 40.5 28.3 4.0 29.2 42.5 28.3
17:0 0.1 100.0 25.0 25.0 0.6 44.4 27.8 27.8
17:1 0.5 35.7 35.7 28.6
18:0 1.0 90.0 20.0 10.0 6.8 54.6 8.8 36.6
18:1 15.2 45.3 16.5 38.2 30.3 36.0 17.0 47.0
18:2 9.3 25.7 25.7 48.6 27.3 26.7 26.8 46.5
18:3 29.8 28.6 22.5 48.9 1.4 33.3 28.6 38.1
Other 1.8 3.6 50.0 46.4
a
Enzymatic stereospecific analysis using modified Brockerhoff method. Data adapted from Christie and Clapperton (1982).
b
Enzymatic stereospecific analysis using Brockerhoff method (1965). Data adapted from Kuksis et al. (1973).
c
Enzymatic stereospecific analysis using modified Brockerhoff method. Data adapted from Parodi (1982).
tr., trace.
5862 TRIGLYCERIDES/Structures and Properties
with 16–18 carbons are more evenly distributed be-
tween the sn-1 and sn-2 positions. According to
Gresti et al. the most common individual triacylgly-
cerol species in bovine milk fat are 4:0–16:0–18:1
(4.2 mol%), 4:0–16:0–16:0 (3.2 mol%), and 4:0–
14:0–16:0 (3.1 mol%), all of which are representa-
tives of the triacylglycerol class consisting of one
butyryl group at the sn-3 position and two long-
chain acyl groups at the sn-1 and sn-2 positions.
0009 The triacylglycerol composition of other rumin-
ants’ (e.g., goat and sheep) milk fat resembles that
of cows’ milk. A high proportion of even-numbered
saturated short-chain fatty acids and fatty acids
with 14–18 carbons, as well as the dominating
amount 18:1 fatty acids among unsaturated fatty
acids of triacylglycerols, is obvious (Table 5). Distri-
bution of fatty acids between the sn-positions is
also similar to bovine milk fat. However, unsatur-
ated fatty acids (18:1–18:3) and saturated 16:0 and
18:0 fatty acids are more evidently esterified in the sn-
3 and sn-1 positions, respectively, than in bovine milk
fat.
0010 One of the main differences between monogastric
mammals (e.g., human, pig, horse) and ruminants’
milk fats is the absence or scarcity of short- and
medium-chain fatty acids in the milk fat of monogas-
tric mammals (Table 5). Also, the amount of diene
and polyene fatty acids is much higher in their milk
fat. Palmitic and oleic acids are the most prominent
saturated and unsaturated fatty acid, respectively, in
monogastric mammals’ milk fat as they are also in
ruminants’ milk fat. High concentration (70%) of
palmitic acid at the secondary position is typical for
human milk fat, as is the esterification of stearic
acid in the sn-1 position. Unsaturated fatty acids are
preferentially acylated in the primary positions of
triacylglycerol molecules.
Depot Fats
0011Triacyglycerol compositions of animal depot fats are
much simpler than those of milk fats, and almost all
fatty acids are very unevenly distributed between the
three sn-positions. In triacylglycerols of lard, c. 85%
of palmitic acid and almost 80% of stearic acid are in
the sn-2 and sn-1 position, respectively. However, all
unsaturated fatty acids are mainly esterified in the
sn-3 position (Table 6).
0012The most characteristic feature of tallow is the
high content (> 25 mol%) of stearic acid, which is
equally distributed between the two primary pos-
itions (Table 6). Palmitic and myristic acids are also
most prominent in the sn-1 and sn-3 position, respect-
ively. In contrast, the main proportion of unsaturated
fatty acids is in the secondary position, c. 90% of
linoleic acid and over 50% of oleic acid.
Egg Yolk
0013Oleic acid, palmitic acid, and linoleic acid, in that
order, consist of nearly 90 mol% of all fatty acids in
triacylglycerols of egg yolk (Table 6). According to
Gornall and Kuksis, the most common triacylglycerol
tbl0006 Table 6 Distribution of fatty acids between the sn-1, sn-2, and sn-3 positions in egg yolk, lard, and tallow triacylglycerols
Fattyacid Total (mol%) Percentage Total (mol%) Percentage
sn-1 sn-2 sn-3 sn-1 sn-2 sn-3
Egg yolk
a
Lard
b
14:0 1.0 33.3 33.3 33.3 1.7 25.0 59.6 15.4
16:0 27.0 77.5 6.3 16.2 28.8 12.0 85.1 2.9
16:1 5.0 41.2 17.6 41.2 2.8 24.3 48.2 26.5
18:0 6.0 35.3 17.6 47.1 12.1 78.8 6.3 14.9
18:1 48.0 14.8 40.1 45.1 43.6 37.5 10.0 52.5
18:2 13.0 7.3 75.6 17.2 10.1 23.7 13.2 63.1
18:3 0.9 51.9 48.1
Ta ll o w
c
14:0 3.4 28.7 14.9 56.4
15:0 0.6 33.3 22.2 44.5
16:0 30.5 47.7 28.2 24.1
16:1 1.9 36.2 13.8 50.0
17:0 1.2 33.3 27.9 38.9
18:0 26.0 44.2 14.5 41.4
18:1 34.9 14.2 52.8 33.0
18:2 1.5 4.6 88.6 6.8
a
Stereospecific enzymatic analysis. Data adapted from Gornall and Kuksis (1971).
b
Stereospecific enzymatic analysis using kinetic resolution with phospholipase C. Data adapted from Myher and Kuksis (1979).
c
Method based on separation of diastereomers of diacylglycerol derivatives on a silica-gel HPLC column. Adapted from Christie et al. (1991).
TRIGLYCERIDES/Structures and Properties 5863
species of egg yolk are 16:0–18:1–18:1 (29 mol%),
16:0–18:2–18:1 (15 mol%), 18:1–18:2–18:1
(7 mol%), and 16:0–18:1–18:0 (7 mol%). Palmitic
and linoleic acids are very unevenly distributed be-
tween the sn-positions: over 70% of 16:0 and 18:2 is
in the sn-1 and sn-2 position, respectively. Stearic acid
is evenly distributed between the primary positions
and oleic acid between the sn-2 and sn-3 positions.
Fish Oils
0014In fish oils, myristic and palmitic acids are esterified
preferentially in the sn-2 position or in the sn-1
position (Table 7). Stearic and palmito-oleic acid are
esterified to a great extent in the sn-1 position or
distributed evenly between the three positions with
a slight preference for sn-1 position. Oleic and
tbl0007 Table 7 Distribution of fatty acids between the sn-1, sn-2, and sn-3 positions in fish oil triacylglycerols
Fattyacid Total (mol%) Percentage Fatty acid Total (mol%) Percentage
sn-1 sn-2 sn-3 sn-1 sn-2 sn-3
Herring
a
Herring
b
14:0 6.7 30.0 50.0 20.0 14:0 9.7 42.0 23.7 34.3
16:0 12.0 33.3 47.2 19.4 16:0 15.7 33.3 39.3 27.4
16:1n-11 0.3 63.0 37.5 0.0
16:1n-9 0.2 14.3 71.4 14.3
16:1 9.3 46.4 35.7 17.9 16:1n-7 5.0 44.1 26.2 29.7
18:0 1.0 33.3 33.3 33.3 18:0 0.9 34.6 34.6 30.8
18:1 11.3 47.1 29.4 23.5 18:1n-9 9.9 39.0 30.0 31.0
18:1n-7 1.5 55.8 18.6 25.6
18:1n-5 0.5 42.9 35.7 21.4
18:2 2.3 42.9 42.9 14.3 18:2n-6 1.2 33.3 38.9 27.8
18:3n-3 1.4 30.0 40.0 30.0
18:4n-3 3.8 42.2 35.8 22.0
20:1n-11 1.2 38.9 16.7 44.4
20:1 17.0 49.0 11.8 39.2 20:1n-9 11.8 46.7 12.0 41.3
20:5 8.3 12.0 72.0 16.0 20:5n-3 5.9 17.9 62.5 19.6
22:1 23.0 20.3 7.2 72.5 22:1n-11. 16.0 25.1 10.6 64.4
n-13
22:1n-9 0.8 9.1 68.2 22.7
22:5 1.7 20.0 60.0 20.0 22:5n-3 0.5 14.3 85.7 0.0
22:6 1.7 20.0 60.0 20.0 22:6n-3 6.1 12.9 87.1 0.0
24:1n-9 0.7 22.7 13.6 63.6
Mackerel
a
Tuna
c
14:0 6.0 33.3 55.6 11.1 12:0 0.0 92.9 92.9 85.7
16:0 13.7 36.6 51.2 12.2 14:0 3.7 34.4 46.0 19.6
16:1 7.0 52.4 28.6 19.0 15:0 1.3 43.5 41.2 15.3
18:0 2.0 50.0 16.7 33.3 16:0 22.3 53.0 31.5 15.4
18:1 17.0 41.2 17.6 41.2 16:1n-7 5.0 47.8 25.4 26.8
18:2 1.7 40.0 20.0 40.0 17:0 2.3 59.3 33.4 7.3
20:1 10.7 25.0 15.6 59.4 18:0 5.8 69.9 14.3 15.8
20:5 9.0 18.5 44.4 37.0 18:1n-9 15.5 40.1 15.0 44.9
22:1 15.7 38.3 10.6 51.1 18:2n-6 1.6 33.7 27.5 38.7
22:5 1.7 20.0 60.0 20.0 18:3n-6 0.1 4.8 52.4 42.9
22:6 2.3 28.6 0.0 71.4 20:0 0.4 30.1 10.5 59.4
Cod
a
18:3n-3 0.5 21.9 24.0 54.1
14:0 3.0 22.2 55.6 22.2 20:1n-9 1.1 24.6 18.8 56.6
16:0 10.7 37.5 43.8 18.8 20:2n-6 0.3 24.4 27.8 47.8
16:1 9.3 39.3 28.6 32.1 20:3n-6 0.1 38.5 23.1 38.5
18:0 2.3 71.4 14.3 14.3 22:0 0.3 33.3 12.8 53.8
18:1 23.0 50.7 13.0 36.2 20:4n-6 2.1 12.9 44.2 42.9
18:2 1.3 25.0 25.0 50.0 20:5n-3 7.1 15.3 31.2 53.5
20:1 12.0 38.9 22.2 38.9 24:1n-9 0.4 31.5 8.7 59.8
20:5 8.3 12.0 44.0 44.0 22:6 29.9 9.9 47.4 42.7
22:1 10.3 38.7 25.8 35.5 Other 0.2 82.7 15.0 2.3
22:5 1.7 20.0 60.0 20.0
22:6 2.3 42.9 28.6 28.6
a
Enzymatic stereospecific analysis. Adapted from Brockerhoff et al. (1968).
b
Method based on separation of enantiomers of monoacylglycerol derivatives on a chiral HPLC column. Adapted from Takagi and Ando (1991).
c
Method based on separation of enantiomers of diacylglycerol derivatives on a chiral HPLC column. Adapted from Myher et al. (1996).
5864 TRIGLYCERIDES/Structures and Properties
eicosenoic acids are esterified predominantly in the
primary positions with a higher proportion in the sn-
1 position. Also, docosenoic acid is esterified abun-
dantly in the primary position, but with a higher
proportion in the sn-3 position in most fish species.
Linoleic acid is esterified preferentially in the sn-2 or
sn-3 positions. Eicosapentaenoic acid is preferably in
the sn-2 or sn-3 positions, docosapentaenoic acid in
the sn-2 position, and docosahexaenoic acid in one of
the three positions.
Triacylglycerol Structure of Modified Fats
and Structured Lipids
0015 Modification of fats and oils has been studied exten-
sively in order to improve their physical, chemical,
and nutritional properties, and to make them more
suitable for manufacture of fat products with desired
properties. Generally used methods of modification
that change the fatty acid composition of fat or
oil, are hydrogenation, fractionation, and blending.
In the last two decades, interest has focused on
the lipase-catalyzed interesterification reactions. The
change in the distribution of fatty acids between the
three positions of glycerol backbone depends on
the regiospecificity of the lipase catalyst. When a
nonspecific lipase is used, the specific distribution of
fatty acids of a natural fat changes to a random
distribution. A similar product is obtained to that in
chemical randomization. The change in triacylgly-
cerol composition depends on the type of interester-
ification reaction. Ester–ester exchange is a reaction
between two or more esters, for example triacylgly-
cerols of plain fat or oil (intramolecular interesterifi-
cation). The acidolysis reaction is a reaction between
triacylglycerol and free fatty acid, in which an
exchange of acyl groups takes place. In alcoholysis
reaction, an acyl group is changed between an
acylglycerol and an alcohol. Lipase-catalyzed modifi-
cation of milk fat has been reviewed, including indus-
trial applications for the manufacture of lipolyzed milk
and cheese flavor products and the research efforts
with the aim to improve nutritional and technological
properties based on ester–ester exchange, acidolysis,
and alcoholysis reactions.
0016The following definitions have been used for
structured lipids: Structured lipids are modified or
synthetic oils and fats containing both long-chain
(mainly essential) fatty acids and medium- or short-
chain fatty acids. Specific structured lipids are modi-
fied or synthetic oils and fats containing long-chain
(mainly essential fatty acids) and medium- or short-
chain fatty acids, in which each group is located
specifically at the sn-2 position or sn-1,3 positions
of the glycerol backbone. Specific structured lipids
can be produced only by interesterification reactions
catalyzed by regiospecific lipases.
0017As examples of industrial applications of lipase-
catalyzed reactions, the manufacture of cocoa butter
equivalent and human milk substitute are briefly de-
scribed here. In cocoa butter, 87% of oleic acid is
esterified in the sn-2 position, and 97% of palmitic
and 98% of stearic acid is esterified in the primary
positions (Table 3), and the three major molecu-
lar species are 16:0–18:1–16:0, 18:0–18:1–18:0, and
16:0–18:1–18:0. This specific distribution of fatty
acids is reflected in the unique melting characteris-
tics with a narrow melting range. Using 1,3-specific
lipase to catalyze the reaction between oils, in which
oleic acid is in the sn-2 position, and saturated acyl
donors, a cocoa butter substitute, can be produced,
with triacylglycerol composition and melting proper-
ties very similar to those of cocoa butter. In human
milk, 70% of palmitic acid and in cows’ milk 45%
of palmitic acid is esterified in the sn-2 position
(Table 5). The unique fatty acid distribution plays
an important role in the nutrition of newborn.
During ingestion, lipases hydrolyze the fatty acids
esterified in the sn-1 and sn-3 position, and 2-mono-
acylglycerols and free fatty acids are absorbed. How-
ever, a part of the long-chain fatty acids is precipitated
in the gut as calcium salts, leading to the loss of
long-chain fatty acids and calcium. To overcome the
problems of palmitic acid absorption, a human milk
fat substitute, which closely resembles the specific
structure of human milk fat, is produced from
tbl0008 Table 8 Properties of the main polymorphic forms of triacylglycerols
Property a-Polymorph b
0
-Polymorph b-Polymorph
Molecular packing in the crystal Hexagonal Orthorhombic Triclinic
X-ray diffraction, short spacing 4.15A
˚
4.2 and 3.8A
˚
4.6A
˚
Infrared spectroscopy Single band at 720 cm
1
Double band at 727 and 719 cm
1
Single band at 717 cm
1
Melting point (
C)
TG 24:0 (tricaprylin) 51.0 18.0 þ10.0
TG 30:0 (tricaprin) 10.5 þ17.0 þ32.0
TG 48:0 (tripalmitin) þ45.0 þ56.5 þ66.0
TG 54:0 (tristearin) þ54.7 þ64.0 þ73.3
TRIGLYCERIDES/Structures and Properties 5865
vegetable oil in a reaction catalyzed by a 1,3-specific
lipase.
Properties of Triacylglycerols
Physicochemical Properties
0018 The melting and crystallization properties of tri-
acylglycerols of food fats and oils are of paramount
interest in the food industry in manufacturing fatty
foods. They are influenced by fatty acid composition,
acyl distribution, molecular size, and polymorphism
of triacylglycerols. Most triacylglycerols of natural
fats and oils consist of straight-chain fatty acids with
an even number of carbon atoms, 18:1, 18:2, and
16:0 being the most abundant. Double bonds are
almost exclusively in cis-configuration, but rumin-
ants’ milk fats with a significant amount of trans-
fatty acids are a rare exception. In polyene fatty
acids, methylene-interrupted double bonds are most
common, but conjugated double bonds are found in
significant amounts in milk fat and other fats of
animal origin. Substituted fatty acids are uncommon
among natural fats and oils.
0019 The crystallization properties of triacylglycerol
mixtures at ambient temperatures are strongly associ-
ated with the amount of trisaturated triacylglycerols,
but also, triacylglycerol species consisting of two sat-
urated, long-chain fatty acids and one trans-monoene
fatty acid influence the solidification properties. A
strong positive correlation between softening point
and content of trisaturated triacylglycerols has been
detected in relatively simple fats and oils, but the
situation is more complicated with more complex
triacylglycerol mixtures. For example, no significant
correlation between the softening point and the
amount of trisaturated triacylglycerol in milk fat was
observed, indicating the importance of the compos-
ition of the trisaturated fraction. In milk fat, a decrease
in softening point is associated with an increase in the
proportion of short-chain trisaturated triacylglycerols
(TG 26–32) and a decrease in the proportion of long-
chain trisaturated triacylglycerols (TG 44–54). In the
1960s, deMan and colleagues demonstrated the effect
of the distribution of fatty acids between the sn-pos-
itions on the melting and solidification properties of
triacylglycerols by randomizing the highly specific
fatty acid distribution of milk fat using chemical inter-
esterification. Although the treatment did not affect
the fatty acid composition or the proportion of trisa-
turated triacylglycerols of milk fat, it resulted in an
increased softening point, hardness, and content of
high-melting-point triacylglycerols in milk fat.
0020 Polymorphism is a common phenomenon for or-
ganic compounds consisting of long aliphatic carbon
chains resulting in various packing of molecules in the
crystal lattices, hence the multiple melting points of
polymorphic forms of both pure triacylglycerols crys-
tals and compound crystals of various triacylglycerols
in natural fats and oils. The main polymorphic forms
of triacylglycerols are named a, b
0
, and b. Generally,
the a polymorph is the least stable, and the b poly-
morph is the most stable, but all of them can be
found in crystallized food fats in appropriate condi-
tions. Some of their properties and examples of dif-
ferences between melting points of polymorphs of
pure medium-chain and long-chain triacylglycerols
are presented in Table 8. A schematic presentation
of possible phase transitions from liquid to solid, and
from solid to solid is shown in Figure 3.
Technological Properties
0021The importance of fatty acid composition of triacyl-
glycerols is clearly demonstrated in oxidative and
hydrolytic deterioration (lipolysis). Oxidative stability
increases in the order polyunsaturated > monounsatur-
ated < saturated fatty acids. The methylene-group
(-CH
2
-) between double bonds in polyunsaturated
fatty acids is especially sensitive for radical
formation, and thus initiation of autooxidation of
fats and oils.
0022In addition to fatty acid composition, the distribu-
tion of fatty acids in triacylglycerols together with
molecular size is important in hydrolytic deterioration
catalyzed by lipases (EC 3.1.1.3). Several techno-
logically meaningful lipases hydrolyze fatty acids ex-
clusively from the primary positions and attack more
rapidly at small triacylglycerols. Because of the spe-
cific fatty acid distribution in most food fats and oils,
the composition of free fatty acids differs markedly
from that of intact fat. This is most pronounced in
lipolysis of bovine milk fat. Most triacylglycerols
in bovine milk fat (over 30 mol%) are relatively
small molecules containing at least one short-chain
Liquid Solid Solid
Molten state α
β
β
β'
β'
β
Molten state
Molten state
fig0003Figure 3 Possible transitions between liquid and solid, and
between different polymorphic forms.
5866 TRIGLYCERIDES/Structures and Properties
fatty acid esterified in the sn-3 position, resulting in
rapid liberation of highly unpleasant-tasting and
technologically problematic butyric and caproic
acids into the media.
0023 Rheological properties of spreads are greatly
affected by the composition of raw materials, crystal-
lization of emulsion (initial and final temperature,
cooling rate, duration of crystallization), mechanical
treatments, and configuration of manufacturing
equipment. However, the polymorphism of triacyl-
glycerols also has a substantial effect on the consist-
ency and organoleptic acceptability of spreads. A
rapid cooling rate of fats with complex fatty acid
and triacylglycerol composition, e.g., milk fat, results
in the formation of a polymorphs with rather fragile
small crystals. Because of a larger mobility of mol-
ecules within the crystal lattice of the a polymorph,
triacylglycerol molecules, even with a large difference
between the chain length of acyl groups, are able to fit
into the crystal lattice, and so a large amount of fat
will crystallize initially. a crystals are very unstable
and will usually transform into more stable poly-
morphs very rapidly. A slower cooling rate of fats
with a simpler and more coherent triacylglycerol
composition, e.g, cocoa butter, favor the formation
of more stable b
0
and b polymorphs. Small and nee-
dlelike crystals of b
0
polymorph are desirable in
spreads, because they increase plasticity of the prod-
ucts. In baked products, they aid creaming by incorp-
orating large amounts of air in the form of small
air bubbles into the structure. A decrease in the
chain length variety enables the formation of a highly
ordered crystal structure, increasing the probabiblity
of crystallization of triacylglycerols straight into the
most stable b polymorph. b crystals are larger than
those of b
0
and may lead to undesirable sandiness in
spreads. The influence of technological modification
of food fats on polymorphism has been demon-
strated. For example, an increase in the proportion
of liquid canola oil in butterfat decreased the amount
of b
0
polymorph in the mixture. Further, interesterifi-
cation of butter resulted in crystallization of butterfat
in the b
0
polymorphic form.
0024 Marangoni and Rousseau emphasized that, al-
though the triacylglycerol structure, solid–liquid
ratio, and polymorphism greatly affect the rheo-
logical properties of spreads, the microstructure of
the fat crystals network, i.e, aggregates of fat crystals
and their interaction, is of paramount importance in
the viscoelastic properties of spreads. The elastic
properties of crystal network and of individual aggre-
gates influence the overall rheology of spreads. The
formation of large crystals and further aggregation of
the crystals in the form of spherulites (Ostwald
ripening) are energetically favorable. The differences
in aggregate formation could not be explained suffi-
ciently by changes in polymorphism. Rousseau et al.
suggested that the viscosity of the liquid phase, com-
position, and tempering have a more pronounced
effect on the aggregation of spherulites than poly-
morphism.
0025The addition of milk fat or its fractions in choc-
olates or in imitation chocolates (compound coatings)
is another important application in which modifica-
tion of the composition of triacylglycerol mixture,
and hence polymorphism of triacylglycerols, has an
important role. Cocoa butter, the main component of
chocolate, with three major triacylglycerol species,
i.e., 16:0–18:1–16:0, 18:0–18:1–18:0, and 16:0–
18:1–18:0, crystallizes mainly in the b polymorphic
form and has six subforms named I–VI. The V poly-
morph is a very stable and desirable form, giving
an excellent appearance (gloss) in chocolates. Poly-
morphic transitions during storage are known to
result in bloom development, i.e., loss of the bright
glossy appearance of chocolates. Milk fat is added
to chocolate in order to prevent blooming, soften
the chocolate, and improve the flavor. The addition
of anhydrous milk fat or high-melting-point fractions
of milk fat in dark chocolate inhibits both the rate of
bloom development and the time for the onset
of visible blooming, which is most likely related to
changes in the phase behavior and crystallization kin-
etics. The softening effect of milk-fat addition is due
to the increase in the amount of stable b
0
polymorph
resulting from the more complex triacylglycerol
structure and the increase in the proportion of low-
melting-point triacylglycerols. Up to 30% of milk fat
can be added to cocoa butter without resulting in
extreme softening.
Triacylglycerol Structure and Fat Metabolism
0026When a chiral triacylglycerol with three different es-
terified fatty acids enters the upper intestinal tract,
lingual and gastric lipases catalyze the hydrolysis of
some of the fatty acids in the sn-3 position, producing
1,2-diacyl-sn-glycerol and free fatty acid. The short-
chain acyls at the sn-3 position are easily hydrolyzed
by gastric lipases. A mixture of triacylglycerol pro-
ceeds to the small intestine. Pancreatic lipase and its
colipase hydrolyze the fatty acid from the sn-1 position
of the 1,2-diacyl-sn-glycerol, and 2-monoacylglycerol
and free fatty acid are formed. Pancreatic lipase also
hydrolyzes the triacylglycerol that was not hydrolyzed
by the gastric lipase, slightly preferentially in the sn-1
position producing 2,3-diacyl-sn-glycerol and free
fatty acid. The 2,3-diacyl-sn-glycerol is hydrolyzed
further by carboxyl ester hydrolase or pancreatic
lipase, and 2-monoacylglycerol and free fatty acid
TRIGLYCERIDES/Structures and Properties 5867