BLBS102-c34 BLBS102-Simpson March 21, 2012 14:7 Trim: 276mm X 219mm Printer Name: Yet to Come
34 Rye Constituents and Their Impact on Rye Processing 667flours with highα-amylase activity give a soft, sticky dough,
which may be too fluid to process into bread or results in a
doughlike crumb. Therefore, preharvest sprouting, which goes
hand in hand with highα-amylase activity, is disadvantageous
for rye flour quality. Rye flours with lowα-amylase activity
yield a rigid, stable dough but lead to breads of low volume hav-
ing a dry and firm crumb, resulting in a short shelf life (Autio
and Salmenkallio-Marttila 2001, Fabritius et al. 1997). How-
ever, when rye flours with lowα-amylase activity contain high
levels of total and water-extractable arabinoxylans, better dough
and bread characteristics can be observed (Weipert 1993a). It
is believed that optimum bread-making performance is reached
at an optimal arabinoxylan to starch ratio of 1:16 (Seibel and
Brummer 1991). This ratio provides balanced water-binding ca- ̈
pacity and water distribution in the dough and the bread crumb.
A shift in favor of more arabinoxylan causes stiffening of the
dough (Kuhn and Grosch 1989), due to the high water-holding ̈
capacity of the arabinoxylans. It also results in breads of greater
specific volume and a firmer crumb (K ̈uhn and Grosch 1989). A
shift in favor of starch results in a low dough yield, soft dough,
a flat bread form, a split and tight crumb, and a low shelf life
(Vinkx and Delcour 1996).Arabinoxylans Although many studies have reported conflict-
ing results concerning the functional role of arabinoxylans in the
bread-making process and during storage of breads, they are of
considerable importance for rye bread-making quality.
Rye cultivars with high total arabinoxylan content, particu-
larly when they also have a high water-extractable arabinoxylan
fraction, perform much better in bread making than those with
low arabinoxylan content. This is due to the high water-holding
capacity of the arabinoxylans, which results in a delay in starch
gelatinization and protects starch fromα-amylase degradation,
resulting in a higher volume yield, a better crumb elasticity, and
a longer bread shelf life (Weipert 1993a, 1994, 1997). Small
differences in arabinoxylan content cause differences in water
absorption and significant differences in bread-making perfor-
mance (Hansen et al. 2004, Weipert 1997).
Besides the content of arabinoxylans, their structure also
significantly influences rye bread-making performance. Differ-
ences in arabinoxylan structure, such as degree of branching and
ferulic acid cross-linking, as well as molecular size, may have
influence on water absorption (Hansen et al. 2004). A high de-
gree of branching and a high degree of ferulic acid cross-linking
of arabinoxylans are related to low water absorption in rye flour
(Hansen et al. 2004).
The dough and bread-making properties of rye flour also de-
pend on the type of arabinoxylans present. In general, dough
consistency is negatively related to dough water content. Be-
cause of their high (and similar) water-holding capacities, both
water-extractable and water-unextractable arabinoxylans affect
dough consistency (Kuhn and Grosch 1989). However, the ̈
water-extractable and -unextractable arabinoxylans affect the
bread-making properties of rye flour differently. The water-
extractable arabinoxylans increase bread specific volume and
decrease crumb firmness, whereas the water-unextractable ara-
binoxylans decrease bread specific volume and form ratio andslightly increase crumb firmness (K ̈uhn and Grosch 1989). In-
creased water-extractable to water-unextractable arabinoxylan
ratios result in flatter breads with higher specific volume, softer
crumb, and darker crust (Cyran and Cygankiewicz 2004, Kuhn ̈
and Grosch 1989).
Enzymic breakdown of the water-unextractable arabinoxylans
by endoxylanases to solubilized arabinoxylans with medium to
high molecular weight and with limited depolymerization of the
water-extractable fraction has been reported to improve both rye
(Kuhn and Grosch 1988) and wheat (Courtin et al. 1999) bread- ̈
making performance. The increase in the level of high molecular
weight arabinoxylans in the dough aqueous phase results in an
improved water distribution and facilitation of molecular in-
teractions between the dough constituent macromolecules. The
subsequent increase in viscosity of the dough aqueous phase is
likely to play a positive role in dough rheology and gas retention
(Courtin et al. 1999, Rouau et al. 1994). Kuhn and Grosch (1988) ̈
showed an improved crumb structure, decreased crumb firmness,
increased width to height ratio, and increased loaf volume of rye
bread after enzymic treatment of the water-unextractable arabi-
noxylans. Shelf life is also increased, resulting from an initial
decrease in crumb firmness (K ̈uhn and Grosch 1988). The en-
dogenous arabinoxylan-degrading enzymes of rye might be ac-
tive under the conditions prevailing in rye dough (Hansen et al.
2002, Rasmussen et al. 2001) and in the first part of the oven
phase, thus prior to enzyme inactivation (Rasmussen et al. 2001).
Endogenous enzymes in flour may thus affect crumb properties
such as firmness, elasticity, and stickiness (Nilsson et al. 1997b).
According to Figueroa-Espinoza et al. (2004), the enzymic
release of high molecular weight arabinoxylans may be positive
due to the capacity of the latter to gel and form a polysaccharide
network in the dough, thereby increasing water absorption, gas
retention, bread volume, and shelf life.Proteins Proteins are only of secondary importance for rye
bread-making quality because of their inability to form a gluten
network (Gellrich et al. 2003, 2004b; Kipp et al. 1996; K ̈ohler
and Wieser 2000). However, they should not be neglected, as
they seem to be important at the dough-mixing step, at least for
certain cultivars (Parkkonen et al. 1994). Indeed, although rye
proteins do not form a regular gluten network, they have some
ability to aggregate (Field et al. 1983) and are surface active
(Wannerberger et al. 1997).Sensory Properties of Rye BreadRye bread has a typical strong and slightly bitter flavor. The
most dominant sensory attribute of rye bread is its rye-like fla-
vor, but perceptions of sourness and saltiness are also substan-
tially associated with rye bread (Heini ̈o et al. 1997). The aroma
results from a mixture of many different volatile compounds
formed by enzymic reactions during fermentation and thermal
reactions during baking (Heinio et al. 2003a, 2003b; Kirchhoff ̈
and Schieberle 2001). Besides the generation of aromas dur-
ing these steps, the flour itself is an important source of dough
aroma (Kirchhoff and Schieberle 2002). The specific rye-like
flavor can be slightly modified to have a milder taste, without