Food Chemistry

178 3 Lipids

3.3.2.2 PhysicalProperties

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:

Melting Point (◦C)

β-form

Tripalmitin 65. 5
1,3-Dipalmitin 72. 5
1,2-Dipalmitin 64. 0
1-Palmitin 77. 0
2-Palmitin 68. 5

MG and DG are surface-active agents. Their
properties can be further modified by esterifi-
cation 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, carbohy-
drate). 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 PhosphatidylDerivatives

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 foodsa

Milk Soya Wheat Apple

Total lipids 3. 623. 01. 50. 088

Triacylglycerols 94 88 41 5

Mono-, and diacylglycerols 1. 51

Sterols < 1115

Sterol esters 1 2

Phospholipids 1 .510 20 47

Glycolipids 1 .529 17

Sulfolipids 1

Others 0 .54 7 15

aTotal lipids as %, while lipid fractions are expressed

as percent of the total lipids.