Food Chemistry

15.2 Individual Constituents 701

in Formula 15.4. It was found that GSH reacts
very specifically in dough making because the
intermolecular disulfide bridges involving Cb∗
and Cxin LMW (Fig. 15.10) are reduced to
an extent of 47% in each case. Intramolecular
disulfide bonds are hardly attacked. Since only
one cleavage of intermolecular disulfide bonds
can weaken the gluten and the dough, the strong
rheological effect of GSH is understandable.
The specificity of GSH is very remarkable since
per g of flour, 50–100 nmol of GSH are faced
with about 9000 nmol/g PSSP, which contain
intermolecular disulfide bonds only to an extent
of 10%.

15.2.4 Carbohydrates

15.2.4.1 Starch

The major carbohydrate storage form of cereals,
starch (cf. Table 15.6) occurs only in the en-

Table 15.28.Lipids in various cereal starches

Wheat Corna(maize) Amylomaizea Waxy maizea

(% or mg/100g)b

Nonpolar lipids 6% 60% 73% 88%
Sterol esters 2 3 9 7
Triacylglycerols 15 5 16 12
Diacylglycerols 7 3 16 6
Monoacylglycerols 8 12 13 5
Free fatty acids 27 380 650 105
Glycolipids 5% 1% 5% 6%
Sterol glycosides 3 7 13 3

18

⎫

⎬

⎭

Monogalactosyldiacylglycerols 4 1
Monogalactosylmonoacylglycerols 10
Digalactosyldiacylglycerols 11 2
Digalactosylmonoglycerols 24 17 3

Phospholipids 89% 39% 22% 6%
Lyso-phosphatidyl ethanolamines 104 17 16 1
Lyso-phosphatidyl glycerols 23 6 7 trace
Lyso-phosphatidyl cholines 783 226 183 8
Lyso-phosphatidyl serines 26 8 6 trace
Lyso-phosphatidyl inositols
Total lipids 1,047 667 964 153

aAmylose content in starch amounts to 23% (corn), 70% (amylomaize) and 5% (waxy maize cultivars).
bResults for lipid classes are expressed as % of total lipids present in starch, and for individual lipid compounds

as mg/100g starch dry matter.

dosperm cells. The size and form of the starch

granules are specific for different cereals. The

polysaccharide molecules in starch granules are

radially organized. Due to the presence of alter-

nating amorphous (mainly amylose) and semi-

crystalline layers (amylopectin), differences in in-

dices of refraction can be observed under a micro-

scope.

Starch granules swell when heated in water

suspension. At the end of swelling, they lose

their form; i. e. they gelatinize. The tempera-

ture range in which these changes occur and

also the extent of swelling at a given tem-

perature are characteristic (cf. 4.4.4.14.1) and

may be used for starch source identification.

Starch absorbs ca. 45% of water in the baking

process.

Cereal starches consist of about 25% amylose

and 75% amylopectin (cf. Table 4.20). The chem-

ical structures of these polysaccharides are pre-

sented in 4.4.4.14.3 and 4.4.4.14.4. Starch gran-

ules in some cultivars, for instance waxy corns,

contain only amylopectin, while some cultivars