2009_Book_FoodChemistry

3.3 Acylglycerols 177
in olive oil saturated acyl groups are attached
to position 1 and 3. As proof, the amount of
2-MG containing palmitic acid is determined
after hydrolysis of the triglycerols with a lipase
(pancreas). Values above 2% are indicative of
an adulteration of the olive oil with an ester
oil.
The positional specific distribution of palmitic
acid is unfavorable for the use of fats and oils of
plant origin in infant food, as this acid is liberated
by lipolysis in the gastric tract. Palmitic acid
then forms insoluble salts with Ca 2+ -ions from
the food, possibly resulting in severe bilious attacks.
The fatty acids of human milk consist of
up to 25% of palmitic acid; 70% are bound to
the 2-position of the triglycerols. During lipolysis
2-monopalmitin is formed that is easily resorbed.
3.3.1.5 Biosynthesis
A TG molecule is synthesized in the fat cells
of mammals and plants from L-glycerol-3-
phosphate and fatty acid-CoA esters (Fig. 3.9).
The L-glycerol-3-phosphate supply is provided
by the reduction of dihydroxy acetone phosphate
by NAD + -dependent glycerol phosphate dehydrogenase.
The dihydroxy acetone phosphate
originates from glycolysis.
The lipid bodies (oleosomes, spherosomes) synthesized
are surrounded by a membrane and are
deposited in storage tissues.
The TG fatty acid composition within a plant
species depends on the environment, especially
the temperature. A general rule is that plants
in cold climates produce a higher proportion
of unsaturated fatty acids. Obviously, the mobility
of TGs is thus retained. In the sunflower
(cf. Fig. 3.10), this rule is highly pronounced;
whereas in safflower, only a weak response to
temperature variations is observed (Fig. 3.10).
Fig. 3.9. Biosynthesis of triacylglycerols
els may be increased by the action of hydrolases
during food storage or processing. MG and DG
are produced commercially by fat glycerolysis
(200 ◦ C, basic catalyst)
(3.25)
3.3.2 Mono- and Diacylglycerols (MG, DG)
3.3.2.1 Occurrence, Production
The occurrence of MG and DG in edible oils or
fats or in raw food is very low. However, their lev-
From the equilibrium (cf. Formula 3.25) that
contains 40–60% MG, 45–35% DG and 15–
5% TG, the MG are separated by distillation
under high vacuum. The amount of 1-MG
(90–95%) is predominant over the amount
of 2-MG.