Food Chemistry

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

Triacylglycerola Found Calculated Triacylglycerola Found Calculated

β-StOSt 0. 30. 5 β-OStL 0. 50. 2
β-StStO 0. 2 trace β-OOL 8. 16. 5
β-StOO 2. 31. 6 β-OLO 3. 14. 2
β-OStO 0. 1 trace β-StLL 13. 214. 0
β-StStL 0. 30. 2 β-LStL 1. 30. 3
β-StLSt 2. 21. 7 β-OLL 20. 421. 9
OOO 1. 31. 2 β-LOL 8. 48. 7
β-StOL 4. 44. 2 LLL 28. 128. 9
β-StLO 4. 05 .3Others 0. 90. 9

St: Stearic, O: oleic, and L: linoleic acid.
aPrefixβ: The middle fatty acid is esterified at theβ- 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 deter-
mined. 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 esteri-

fied primary OH-groups of glycerol can be differ-

Fig. 3.8.Enzymatic stereospecific analysis of triacylglycerols

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 un-

der controlled conditions to a diacylglycerol

using pancreatic lipase (cf. 3.7.1.1). Phospho-

rylation 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.