Food Chemistry

15.4 Baked Products 715

Fig. 15.29.Extensograms of a normal(I)and weak
dough(II). For quality assessment the following par-
ameters are determined: resistance to extension, height
of the curve at its peak (B–C) given in extensogram
units (EU); extensibility, abscissa length between A–C
in mm; extension area (A–B–C–A, cm^2 ) is related to
energy input required to reach the maximum resistance;
extensogram number (overall dough quality) is the ratio
of extension resistance to extensibility

ble 15.41), form, crumb structure and elasticity,
and the taste of the baked product are evaluated.
A baking test is performed with 1000 g flour for
each product.
When the effects of expensive and not readily
available flour constituents and/or additives are
tested or a new cultivar is assessed, of which
only several hundred kernels are available, a “mi-
cro baking test” is used, with 10 g flour for each
baked product (cf. Fig. 15.35). If even less mate-
rial is available, 2 g are sufficient. The sample is
then kneaded in a mixograph and baked in a cap-
sule.

15.4.1.2 Rye Flour

The Falling Number test (cf. 15.4.1.1.1) and an
amylographic assay are the most important tests
to assess the baking properties of rye flour. These
tests depend to a great extent on gelatinization
properties of starches and the presence ofα-amyl-
ase. The higher theα-amylase activity, the lower
the Falling Number.
An amylograph is a rotational torsion viscometer.
It measures the viscosity change of an aqueous
suspension of flour as a function of tempera-
ture. The recorded curve, called an amylogram
(Fig. 15.30), shows that with increasing tempera-
ture there is an initial small fall followed by
a steep rise in viscosity to a maximum value. The
steep rise is due to intensive starch gelatinization.

Fig. 15.30.Amylograms of two rye flours (according to

H. Stephan, 1976)

Gelatinization Gelatinizationα-Amylase

maximum (peak) temperature

Flour I 720 AU 67 ◦Chigh

Flour II 520 AU 73. 5 ◦Clow

AU: amylogram units.

The viscosity value and temperature at maximum

viscosity (i. e., the temperature reflecting the end

of gelatinization) are then read.

In rye flour with balanced baking properties,

an optimal relationship should exist between

α-amylase activity and starch quality. The extent

of enzymatic starch degradation influences the

stabilty of the gas-cell membranes which are

formed by gas released in the dough and which

consolidate during baking into an elastic crumb

structure. These membranes contain pentosans,

proteins and intact starch granules in addition

to gelatinized and partially hydrolyzed starch.

Highα-amylase activity in rye or a large dif-

ference between the temperatures needed for

enzyme inactivation (close to 75◦C) and those

required for termination of starch gelatinization

will produce poor bread since too much starch

will be degraded during breadmaking. The

gas-cell membranes are liquefied to a great

extent; so the gas can escape. This gas will

then be trapped in a hollow space below the

bread crust (I in Fig. 15.30). Lowα-amylase

activity, especially in conjunction with low starch

gelatinization, leads to a firm and brittle crumb

structure.