Food Biochemistry and Food Processing

27 Bakery and Cereal Products 617

important aspects in fermented bakery products. The
amount and type of some of the proteins is impor-
tant for the formation of an elastic dough and for its
gas-retaining properties. Other proteins in cereals
are enzymes with specific functions, not only for the
developing germ, but also for various changes that
take place from the processing of flour to bakery
products.

Gluten Proteins

The unique storage proteins of wheat are also the
functional proteins in baking. The gliadins and
glutenins, collectively called gluten proteins, make
up about 80% of the total protein in the grain and are
mostly found in the endosperm. These proteins have
very limited solubility in water or salt solutions,
unlike albumins and globulins (Fig. 27.1). A good
bread flour (known as “strong” flour) must contain
adequate amounts of gluten proteins to give the
desired dough characteristics, and extra gluten may
be added to the bread formulation.

Enzyme Proteins

The albumin and globulin proteins are concentrated
in the bran, germ, and aleurone.

Amylases The primary function of starch-
hydrolyzingenzymes is to mobilize the storage poly-
saccharides to readily metabolized carbohydrates
when the grain germinates (Hoseney 1998).
-amylase hydrolyzes-1,4 glycosidic bonds at
random in the starch molecule chain but is unable to
attack the-1,6 linkages at the branching points on

the amylopectin molecule. The activity of-amylase

causes a rapid reduction in size of the large starch

molecule, and the viscosity of a heated solution or

slurry of starch is greatly decreased. It is most active

on gelatinized starch, but granular starch is also

slowly degraded.

-amylase splits off two glucose units (maltose)

at a time from the nonreducing end of the starch

chain, thus providing a large amount of fermentable

carbohydrate. -amylase is also called a saccharify-

ing enzyme since its action causes a marked in-

crease in sweetness of the hydrated cereal. Neither

the hydrolysis of amylopectin nor of amylose is com-

pleted by -amylase, since the enzyme is not able to

move past the branching points. The presence of

both - and -amylases, however, leads to a much

more comprehensive hydrolysis, since -amylase

produces several new reducing ends in each starch

molecule.

The level of -amylase is very low in intact grain

but increases markedly on germination, whereas -

amylase levels in intact and germinated grain are

similar.

Flour containing too much -amylase absorbs

less water and therefore results in heavy bread. In

addition, the dough is sticky and hard to handle, and

the texture of the loaf is usually faulty, having large

open holes and a sticky crumb texture. However,

some activity is required, and bakers may add amy-

lase either as an enzyme preparation or as wheat or

barley malt in order to slightly increase loaf volume

and improve crumb texture. The thermal stability of

amylases from different sources dictates their activity

during the baking process. Microbial amylases with

greater thermal stability have been used in bread to

Figure 27.1.Wheat proteins.