Food Chemistry

15.2 Individual Constituents 705

Table 15.32.Nonstarch lipids in wheat flour

mg/100ga

Nonpolar lipids(59%)
Sterol lipids 43
Triacylglycerols (TG) 909
Diacylglycerols (DG) 67
Monoacylglycerols (MG) 53
Free fatty acids (FFA) 64

Glycolipids(26%)
Sterol glycosides 18
Monogalactosyldiacylglycerols 115
(MGDG)
Monogalactosylmonoacylglycerols
(MGMG) 17
Digalactosyldiacylglycerols (DGDG) 322
Digalactosylmonoacylglycerols 52
(DGMG)
[3pt]Phospholipids(15%)
N-Acyl-phosphatidyl ethanolamines 95
N-Acyl-lyso-phosphatidyl 33
ethanolamines
Phosphatidyl ethanolamines
Phosphatidyl glycerols 19
Phosphatidyl cholines 96
Phosphatidyl serines
Phosphatidyl inositols 9
Lyso-phosphatidyl glycerols 5
Lyso-phosphatidyl cholines 29

aBased on dry matter.

The neutral lipids are present in flour in the form
of spherosomes and their membranes are formed
by a part of the phospholipids. The spherosomes
can be extracted with nonpolar solvents. The
other phospholipids and all the glycolipids
form inverse hexagonal phases (cf. 8.15.2.2),
which are only partly extractable. During dough
making, the water added results in the conversion
of the inverse hexagonal to a laminar phase,
which in turn stabilizes a microemulsion of the
neutral lipids. The microemulsion vesicles are
enclosed by the network of gluten proteins and,
consequently, difficult to extract. If the dough
is suspended in water, the lipids appear in the
aqueous phase that separates on ultracentrifuga-
tion only when the framework of gluten proteins
has been destroyed by reduction, e. g., with
dithiothreitol.

Other hypotheses which explain the decreasing

extractability of free lipids by selective binding,

e. g., of glycolipids to starch and gluten, have not

been confirmed.

The gas-holding capacity of doughs and, after

passing through a minimum, the baking volume

(Fig. 15.20) are positively influenced by polar

lipids. Two effects are assumed in explanation.

The polar lipids get concentrated in the bound-

ary layer gas/liquid and stabilize the gas bub-

bles against coalescence. In addition, the lipid

vesicles seal the pores which are formed in the

protein films on kneading. On the other hand,

the nonpolar lipids generally negatively influence

the backing result with most varieties of wheat

(Fig. 15.20).

Carotenoids and tocopherols belong to the

minor components of the cereal lipid fraction.

Wheat flour has a carotenoid content averag-

ing 5.7mg/kg. In durum wheats, which have

a more intense yellow color, the carotenoids are

7 .3mg/kg of flour.

The major carotenoid, lutein (cf. 3.8.4.1.2),

is present in free or esterified form (either

mono or diester) with the fatty acids listed in

Table 15.31). The following carotenoid pigments

are also present:β-carotene, β-apo-carotenal,

cryptoxanthin, zeaxanthin and antheraxanthin

(for structures see 3.8.4.1). Carotenoid content

of corn, depending on the cultivar, is 0.6–

57 .9mg/kg, with lutein and zeaxanthin being the

major constituents.

Fig. 15.20.The effect of free nonstarch lipids on

the baking quality of defatted wheat flour (according

toMorrison, 1976). — Lipids (total),−◦–◦– nonpolar

lipids, –•–•– polar lipids