2009_Book_FoodChemistry

3.3 Acylglycerols 175
Table 3.15. Triacylglycerol composition (mole-%) of a sunflower oil.
A comparison of experimental values with calculated values based on a 1,3-random-2-random hypothesis
Triacylglycerol a Found Calculated Triacylglycerol a Found Calculated
β-StOSt 0.3 0.5 β-OStL 0.5 0.2
β-StStO 0.2 trace β-OOL 8.1 6.5
β-StOO 2.3 1.6 β-OLO 3.1 4.2
β-OStO 0.1 trace β-StLL 13.2 14.0
β-StStL 0.3 0.2 β-LStL 1.3 0.3
β-StLSt 2.2 1.7 β-OLL 20.4 21.9
OOO 1.3 1.2 β-LOL 8.4 8.7
β-StOL 4.4 4.2 LLL 28.1 28.9
β-StLO 4.0 5.3 Others 0.9 0.9
St: Stearic, O: oleic, and L: linoleic acid.
a Prefix β: The middle fatty acid is esterified at the β- or sn-2-position, the other two acids are at the sn-1 or
sn-3 positions.
fatty acids bound at positions 1 and 3 are determined.
The fatty acids in position 2 are calculated
from the difference between the total acids and
those acids in positions 1 and 3.
Table 3.15 illustrates the extent of agreement for
the TG composition of sunflower oil obtained
experimentally and by calculation using the
1,3-random-2-random hypothesis. However, both
approaches disregard the differences between
positions 1 and 3. In addition, the hypothesis
is directed to plants, of which the fats and oils
consist of only major fatty acids.
Stereospecific Analysis. Biochemically, the esterified
primary OH-groups of glycerol can be differ-
entiated from each other; thus, the determination
of fatty acids in positions 1, 2 and 3 is possible.
The reactions carried out are presented in
Fig. 3.8. First, the TG (I) is hydrolyzed under
controlled conditions to a diacylglycerol
using pancreatic lipase (cf. 3.7.1.1). Phosphorylation
with a diacylglycerol kinase follows.
The enzyme reacts stereospecifically since it
phosphorylates only the 1,2- or (S)- but not
the 2,3-diglycerol. Subsequently, compound I
is hydrolyzed to a monoacylglycerol (III). The
distribution of the acyl residues in positions 1,
2 and 3 is calculated from the results of the
fatty acid analysis of compounds I, II and III.
Fig. 3.8. Enzymatic stereospecific analysis of triacylglycerols