Food Chemistry

3 Lipids

3.1 Foreword

Lipids are formed from structural units with
a pronounced hydrophobicity. This solubility
characteristic, rather than a common structural
feature, is unique for this class of compounds.
Lipids are soluble in organic solvents but not
in water. Water insolubility is the analytical
property used as the basis for their facile
separation from proteins and carbohydrates.
Some lipids are surface-active since they are
amphiphilic molecules (contain both hydrophilic
and hydrophobic moieties). Hence, they are polar
and thus distinctly different from neutral lipids.
The two approaches generally accepted for lipid
classification are presented in Table 3.1.
The majority of lipids are derivatives of fatty
acids. In these so-called acyl lipids the fatty
acids are present as esters and in some minor
lipid groups in amide form (Table 3.1). The acyl
residue influences strongly the hydrophobicity
and the reactivity of the acyl lipids.
Some lipids act as building blocks in the for-
mation of biological membranes which surround
cells and subcellular particles. Such lipids occur
in all foods, but their content is often less than 2%
(cf. 3.4.1). Nevertheless, even as minor food con-
stituents they deserve particular attention, since
their high reactivity may strongly influence the
organoleptic quality of the food.
Primarily triacylglycerols (also called trigly-
cerides) are deposited in some animal tissues
and organs of some plants. Lipid content in such
storage tissues can rise to 15–20% or higher and
so serve as a commercial source for isolation of
triacylglycerols. When this lipid is refined, it is
available to the consumer as an edible oil or fat.

The nutritive/physiological importance of lipids
is based on their role as fuel molecules (37 kJ/g
or 9 kcal/g triacylglycerols) and as a source of
essential fatty acids and vitamins. Apart from
these roles, some other lipid properties are
indispensable in food handling or processing.

Table 3.1.Lipid classification

A. Classification according to “acyl residue”

characteristics

I. Simple lipids (not saponifiable)

Free fatty acids, isoprenoid lipids (steroids, caro-

tenoids, monoterpenes), tocopherols

II. Acyl lipids Constituents

(saponifiable)

Mono-, di-, triacyl-

glycerols Fatty acid, glycerol

Phospholipids

(phosphatides) Fatty acid, glycerol or

sphingosine, phosphoric

acid, organic base

Glycolipids Fatty acid, glycerol or

sphingosine, mono-, di- or

oligosaccharide

Diol lipids Fatty acid, ethane, pro-

pane, or butane diol

Waxes Fatty acid, fatty alcohol

Sterol esters Fatty acid, sterol

B. Classification according to the characteristics

“neutral–polar”

Neutral lipids Polar (amphiphilic) lipids

Fatty acids (>C 12 ) Glycerophospholipid

Mono-, di-, triacyl-

glycerols Glyceroglycolipid

Sterols, sterol esters Sphingophospholipid

Carotenoids Sphingoglycolipid

Waxes

Tocopherolsa

aTocopherols and quinone lipids are often considered

as “redox lipids”.

These include their melting behavior and the

pleasant creamy or oily taste that is recognized

by a receptor, which has recently been identified.

Therefore, there are all together six taste qualities

(cf. 8.6.1). – Fats also serve as solvents for certain

H.-D. Belitz · W. Grosch · P. Schieberle,Food Chemistry 158
© Springer 2009