2009_Book_FoodChemistry

178 3 Lipids
3.3.2.2 Physical Properties
MG and DG crystallize in different forms
(polymorphism; cf. 3.3.1.2). The melting point
of an ester of a given acid increases for the series
1,2-DG < TG < 2-MG < 1,3-DG < 1-MG:
Tripalmitin 65.5
1,3-Dipalmitin 72.5
1,2-Dipalmitin 64.0
1-Palmitin 77.0
2-Palmitin 68.5
Melting Point ( ◦ C)
β-form
MG and DG are surface-active agents. Their
properties can be further modified by esterification
with acetic, lactic, fumaric, tartaric or
citric acids. These esters play a significant role as
emulsifiers in food processing (cf. 8.15.3.1).
3.4 Phospho- and Glycolipids
3.4.1 Classes
Phospho- and glycolipids, together with proteins,
are the building blocks of biological membranes.
Hence, they invariably occur in all foods of
animal and plant origin. Examples are compiled
in Table 3.17. As surface-active compounds,
phospho- and glycolipids contain hydrophobic
moieties (acyl residue, N-acyl sphingosine) and
hydrophilic portions (phosphoric acid, carbohydrate).
Therefore, they are capable of forming
orderly structures (micelles or planar layers) in
aqueous media; the bilayer structures are found
in all biological membranes. Examples for the
composition of membrane lipids are listed in
Table 3.18.
3.4.1.1 Phosphatidyl Derivatives
The following phosphoglycerides are derived
from phosphatidic acid. Phosphatidyl choline
or lecithin (phosphate group esterified with the
Fig. 3.10. The effect of climate (temperature) on the
fatty acid composition of triacylglycerols
Table 3.17. Composition of lipids of various foods a
Milk Soya Wheat Apple
Total lipids 3.6 23.0 1.5 0.088
Triacylglycerols 94 88 41 5
Mono-, and diacylglycerols 1.5 1
Sterols < 1 1 15
Sterol esters 1 2
Phospholipids 1.510 20 47
Glycolipids 1.5 29 17
Sulfolipids 1
Others 0.54 7 15
a Total lipids as %, while lipid fractions are expressed
as percent of the total lipids.