Bakery Products Science and Technology, Second Edition. Edited by W. Zhou, Y. H. Hui, I. De Leyn,
M. A. Pagani, C. M. Rosell, J. D. Selman, and N. Therdthai.
© 2014 John Wiley & Sons, Ltd. Published 2014 by John Wiley & Sons, Ltd.
Introduction 75
Production and consumption 75
The rye grain 76
Arabinoxylans 77
Bioactive compounds 78
Nutritional value and health-effects 79
Consumption as food 80
Milling products 80
Bread products: rye bread technology 80
Other rye products 82
Flavor of rye grain 82
Chemical compounds influencing
rye flavor 82
Flavor of native rye 82
Flavor formation in processing of rye 83
Summary 83
Acknowledgments 84
References 84
RyeKaisa Poutanen, Kati Katina, and Raija-Liisa HeiniöVTT Technical Research Centre of Finland, Food Biotechnology/Flavour Design, Finland
4
IntroductionRye (Secale cereale L.) is a traditional raw material
used for baking in Northern and Eastern Europe.
The flavor and structure of rye bread are quite dif-
ferent from those of wheat bread, and vary
depending on flour type, other raw materials and
ingredients, process, baking conditions, and time,
as well as on the size and shape of the bread.
Generally consumed as whole grain products, rye
offers a good source of dietary fiber, phenolic
compounds, vitamins, trace elements and minerals.
Rye bread has also been shown to have beneficial
physiological effects especially with respect to glu-
cose metabolism and satiating effects. Expanding
research data strengthen the position of rye grain
as an important raw material for healthy foods,
and the potential for developing novel products is
growing with the knowledge about its transforma-
tions during milling and baking processes.
Production and consumptionIn terms of total production, rye is a minor cereal.
Only about 0.7% of the total cereal grain crop is
rye (FAO 2007). The present world harvest of rye
is about 14.8 million tons, most of which is pro-
duced in the northern part of the region from the
Nordic Sea to the Ural Mountains. Because rye is
extremely winter hardy and can grow in sandy soils
with low fertility, it can be cultivated in areas that
76 CH 4 RYE
are generally not suitable for other cereal crops.
Major producers of rye are Russian Federation,
Poland, Germany, Belarus, and Ukraine. In 2006,
80% of the world’s rye production was in these
five countries (Sahlström and Knutsen 2010).
Food and feed uses of rye are at the same level,
and make up the majority of rye uses (Table 4.1)
Over one-third of the total rye crop is used for
food, predominantly for various types of bread.
Rye consumption in the “Rye Belt” countries is
in the range of 10–30 kg per person per year
(Sahlström and Knutsen 2010).
The rye grainThe basic composition of the rye grain is similar
to that of wheat (Table 4.2). Compared to wheat,
rye generally contains less starch and crude pro-
tein but more dietary fiber (DF). The DF content
of rye is actually the highest among the common
cereals. The major DF constituents of rye are
arabinoxylan (AX), β-glucan, cellulose, fructan,
and lignin (Åman and others 2010). Rye contains
more fructan, mixed-linked β-glucan, and AX but
similar amounts of cellulose and Klason lignin as
compared to wheat (Nilsson and others 1997a).
The range of dietary fiber content in different rye
varieties in the EU-Healthgrain project variety
screen was 20.4–25.2% (Nyström and others
2008). The DF in cereal grains is located mainly
in the outer layers of the kernel, especially in the
bran. Wheat and rye have a similar bran content,
but rye contains more cells within the endosperm,
and thus has a higher DF content (Nyman and
others 1984; Åman and others 1997).
The distribution of rye proteins in the Osborne
solubility classes indicates that in comparison to
wheat, rye contains less glutelins. Rye prolamins,
or secalins, are not considered to play a role in
rye baking either because of their low concentra-
tion or their interactions with other components
(Shewry and Bechtel 2001). Rye starch is similar
in its structure and properties to starches from
wheat and other cereals. It consists of two types
of polymers, amylose and amylopectin, with amy-
lose accounting for 24–26% of total (Shewry and
Bechtel 2001).
The size of rye grains differs between varieties.
Hybrid varieties commonly have larger grains
than population varieties. The main morpholo-
gical characteristics are similar to other grains.
A review on the microstructure of developing
and mature rye grain has been made by Simmonds
and Campbell (1976). The microstructure of
transversely sectioned mature rye grain is shown
in Figure 4.1. The four morphologically differ-
ent tissues of the grain are the layers of pericarp
and seed coat, embryo, aleurone, and starchy
endosperm. The embryo is located on the dorsal
side of the grain. The pericarp consists of ligni-
fied, dead cell layers. The aleurone cells form the
outermost layer of the endosperm and represent
live tissue at maturity. The aleurone layer of rye
is typically only one cell layer thick. Pericarp,
seed coat, and aleurone layer are the main parts
Table 4.1 Uses of rye grain (FAOSTAT 2007. Reproduced
with permission of FAO. )
Type of use Million tonnes %
Feed 6467 43,6
Food 5531 37,4
Seed 1549 10,5
Processing 743 5,0
Other 661 4,5
Table 4.2 Chemical composition of rye (% of dry matter)
Component Rye Wheat 100* Wheat 66**
Ash 2 2 0.5
Fat 2–3 3 1
Protein 10–15 12–14 13
Starch 55–65 67–70 84
Dietary Fibre 19–22 13–17 3
Arabinoxylans 8–10 6
β-Glucan 2–3 0.8
Cellulose 1–3 2.5
Lignin 1–2 0.8
Fructan 4–6 1.4–2.6
(Nyman and others 1984; Andersson, and others 1992; Clydesdale 1994; Härkönen and others 1997; Åman and others 1997, 2010; Boskov-Hansen and others 2003; Fretzdorff and Welge, 2003; Karppinen and others 2003.)*Extraction rate 100 = whole grain flour**Extraction rate 66 = 66% of grain is milled in this flour. This extraction rate corresponds to white wheat flour.
ARABINOXYLANS 77
of the bran fraction produced during milling.
Similarly to wheat and barley, rye contains two
types of starch granules: large lenticular
A-granules (15–25 μm in diameter) and smaller
polygonal B-granules (<10 μm in diameter).
The starchy endosperm constitutes about
80–85% of the weight of the whole kernel, the
embryo 2–3%, and the outer layers about
10–15%. The embryo is located at the basal end
of the grain. The cells of the embryo have thin
walls and contain a large nucleus. They also con-
tain protein bodies and fat globules called
spherosomes. The germ is composed of two func-
tionally different parts: the embryo proper and
the scutellum, which is a shield-like structure
appressed to the endosperm. At germination, the
scutellum becomes a digesting and absorbing
organ that transfers the stored nutrients from
the endosperm to the growing parts of the
embryonic axis.
ArabinoxylansArabinoxylan is the major dietary fiber compo-
nent of rye grain, and contributes remarkably
to the water binding properties of the flour.
The average arabinoxylan content in a set of
18 Swedish rye grain samples was 8.6% (Andersson
and others 2009). The total arabinoxylan contents
in European rye grains varied between 12.1–
14.8% in the bran and 3.1–4.3% in flour (Nyström
and others 2008). The chemistry and solubility of
the arabinoxylans is different in different parts of
the grain. The ratio of soluble to total arabinoxy-
lans is 71% in the endosperm, 25% in the aleurone,
and 14% in the outer bran (Glitsø and others
1995). Furthermore, the ratio of arabinose to
xylose (Ara/Xyl) differs in different parts of the
grain being 0.40 in the aleurone, 0.75 in the
endosperm, and 0.63 in whole rye. Ferulic acid is
esterified to arabinoxylans in rye cell walls (Vinkx
and others 1991).
The arabinoxylans are divided on the basis
of solubility into water-extractable (WE) and
water-unextractable pentosans (WUE). The WE
arabinoxylans are extractable with cold water,
whereas WUE pentosans are alkali soluble. The
percentage of soluble arabinoxylans is higher in
the endosperm than in the bran and shorts frac-
tions (Delcour and others 1989).
Rye arabinoxylans have been classified on the
basis of extractability: Arabinoxylan I has an Ara/
Xyl ratio of 0.5 and it is totally water extractable,
Arabinoxylan II has a Ara/Xyl ratio of 1.4 and it is
partly water-extractable (Bengtsson and Åman
1990). Rye NSP showed significantly higher viscos-
ity in 0.1 M NaCl than in 0.01 M NaCl solution
(Girhammar 1992). Compared with the intrinsic
viscosity of other polysaccharides, the arabinoxylans
Embryo
Aleurone layer
Endosperm
1000 μm
Figure 4.1 The microstructure of rye grain.
78 CH 4 RYE
show a similar value to guar gum (2.3–6.8 dl/g), but
are more viscous than dextran (0.214 dl/g) and gum
arabic (0.12–0.25 dl/g) (Mitchell 1979). Rye varieties
differ in terms of chemical structure and viscosity of
arabinoxylans. Viscosity measurement showed that
Arabinoxylan I fractions from two cultivars were
different due to different proportions of high molec-
ular size polymers (Nilsson and others 2000).
Bioactive compoundsIn addition to macronutrients and DF, grains
contain a wide range of micronutrients and bio-
active compounds. In rye, as well as in other cere-
als, bioactive compounds are concentrated in the
germ and the outer layers of the kernel, which
are also richest in DF (Nilsson and others 1997b;
Glitsø and Bach Knudsen 1999; Liukkonen and
others 2003). The main bioactive compounds in
rye are lignans, phenolic acids, alk(en)ylresorcin-
ols, phytosterols, trace elements and minerals,
folates, tocopherols and tocotrienols and other
vitamins. Table 4.3 shows concentrations of some
major bioactive compounds in rye.
The phenolic compounds in rye grain, as well
as their processed-induced changes and bioavail-
ability and suggested bioactivities have been
reviewed by Bondia-Pons and others 2009. The
phenolic compounds are concentrated in the
outer layers of the grain. Phenolic acids, whereof
ferulic acid the most abundant, are at the highest
concentration of the phenlic compounds in
rye (Table 4.3). Most of the phenolic acids are
present in the grain and flour in bound form,
f.ex. ferulic acid is esterified to arabinoxylan.
A portion of the ferulic acid in the cell wall is
present as dehydrodimers (Faulds and Williamson
1999). The potential health benefits of phenolic
acids are suggested to relate to their antioxidant
activity.
It was long assumed that matairesinol and
secoisolariciresinol are the main plant lignans
also in rye grain. Now it is known that pinoresinol,
syringaresinol, lariciresinol and isolariciresinol
comprise over 80% of the total lignan content of
rye (Heinonen and others 2001). Very recently
also polymeric rye lignans have been detected
(Hanhineva and others 2011). Many of the
lignans are converted by the intestinal microflora
to the mammalian lignans enterodiol and entero-
lactone, which have been linked with various
positive health effects.
Alk(en)ylresorcinols have received particular
interest as potential biomarkers of the intake of
wholegrain rye and wheat products (Ross 2012).
They occur in rye as three major homologs: C17:0
(≈ 24%), C19:0 (≈ 32%) and C21:0 (≈ 24%) (Ross
and others 2003). Alkylresorcinols have been
linked to certain bioactivties, and have also been
found to be incorporated into human erythrocyte
membranes.
Sitosterol is the main sterol in rye (≈ 50%) and
other cereals (Piironen and others 2002, Shewry
and others 2010). The other sterols in rye in
decreasing order are campesterol, sitostanol,
campestanol and sigmasterol. Six folate vitamers
occur in rye. Formylfolates (5-HCO-H4-folate,
10-HCO-H2-folate and 10-HCO-folic acid) and
5-CH3H4-folate are the most abundant vitamers
in rye flour. The R-tocotrienol (38%) and
R-tocopherol (32%) are the major forms of
tocols. The average proportion of tocotrienols
in the Healthgrain variety screen was 59.6% of
the total tocols (Nyström and others 2008).
Processing may influence the level and bioa-
vailability of the bioactive compounds in cereal.
However, knowledge on influence of processing
on levels of bioactive compounds is scarce. Levels
of folate and easily extractable phenolic com-
pounds have been found to increase during
Table 4.3 Concentration of the major bioactive
compounds in rye (μg/g)
Compound Amount Reference
Lignans 19–22 Penalvo et al 2005,
Smeds et al 2007
Phenolic acids 1117–1244 Shewry et al 2010
Alk(en)ylresorcinols 901–1030 Shewry et al 2010
Folates 865–1018 Shewry et al 2010
Tocopherols and
tocotrienols
56–59 Shewry et al 2010
Plant sterols 1110–1233 Shewry et al 2010
NUTRITION AND HEALTH-EFFECTS 79
germination and sourdough baking of rye
(Liukkonen and others 2003a; Kariluoto and
others 2003), whereas levels of phytate (Frölich
and others 1986; Larsson and Sandberg 1991),
alkylresorcinols (Verdeal and Lorenz 1977) and
tocopherols and tocotrienols (Piironen and others
1987; Liukkonen and others 2003a) have been
reported to be reduced in sourdough baking pro-
cess. In our recent study (Liukkonen and others
2003b), the folates were shown to be sensitive to
heat processing (extrusion, autoclaving, puffing,
roasting). However, the folate concentration of
germinated and subsequently heat prosessed rye
grains was still remarkably higher than that of
native grains. The amounts of plant sterols and
lignans changed very little during the heat pro-
cessing. The amounts of tocopherols and tocotrie-
nols and alk(en)ylresorcinols decreased during
the extrusion but remained almost unchanged
during other heat processes. In conclusion, it was
proposed that many of the bioactive compounds
in whole grain rye are stable during food process-
ing, and their levels can even be increased with
suitable processing.
Nutrition and health-effectsDietary guidelines recommend increasing the
intake of whole-grain cereals, but this is still
below the recommendations. Consumed as whole
grain products rye is an important source of DF,
trace minerals, and certain vitamins. In addition
whole grain rye products contain phytochemicals
that together with vitamins, minerals and DF
may have role in disease prevention. In Finland,
about 40% of daily DF intake comes from rye.
From 150 g of whole grain rye bread it is possible
to obtain 40–60%, 22%, 17%, 32–40%, and 43%
of the recommended daily intake of DF, folates,
magnesium, and zinc, respectively.
An increasing amount of research data indi-
cates that rye bread has beneficial physiological
effects. Compared with white wheat bread, whole-
meal rye bread has been shown to reduce the need
for postprandial insulin and to improve first-phase
insulin secretion – both factors associated with the
effective regulation of glucose metabolism and a
reduced risk of type 2 diabetes (Leinonen and
others 1999; Juntunen and others 2002, 2003a,
2003b) – as well as cause changes in adipose tissue
gene function (Kallio and others 2007). Rye prod-
uct consumption has been linked with increased
feelings of satiety (Isaksson and others 2012), and
recent metabolomic data also suggest changes
favorable for weight maintenance (Lankinen and
others 2012).
Rye bread has been shown to improve bowel
function (Gråsten and others 2000; McIntosh and
others 2003), contribute to the growth of bifido-
bacterium, reduce the concentrations of some
compounds that are putative colon cancer risk
markers (Gråsten and others 2000), and increase
the serum concentrations of enterolactone
(Juntunen and others 2000). In epidemiological
studies, a high enterlactone concentration has
been related to a reduced risk of acute coronary
events (Vanharanta and others 1999) and breast
cancer (Ingram and others 1997; Pietinen and
others 2001).
Consumption of rye products has also been
related to possible colon and prostate cancer
risk-reducing effects (Korpela, and others 1992;
Landström, and others 1998; Davies and others
1999; Bylund and others 2000; Gråsten, and others
2000; Mutanen, and others 2000). In the Finnish
study by Pietinen and others (1996), a reduced risk
of death from cardiovascular diseases was related
to the consumption of rye products.
The rye results are consistent with the health
claim that the US Food and Drug Administration
authorized in 1999 for foods that contain 51% or
more whole-grain ingredients. According to the
health claim, “Diets rich in whole-grain foods and
low in total fat and saturated cholesterol may
reduce the risk of heart disease and certain can-
cers”. It is stated that in addition to dietary fiber,
whole-grain foods contain abundant amounts of
antioxidant vitamins and phytochemicals that
seem to act together to provide protective effects.
In Europe, the European Food Safety Authority
(EFSA) has recently accepted a health claim
about the consumption of rye fiber and changes
in bowel function (EFSA, 2011).
80 CH 4 RYE
Consumption as foodAs already stated above, rye is, in contrast to
wheat, a special grain, because it is mostly con-
sumed as whole grain flour in breads and other
cereal products. Examples of products commer-
cially available to consumers and their ingredi-
ents are shown in Table 4.4.
Milling products
Although grains have been used whole in various
ways as human food, usually they have been
ground in preparation for cooking. Most rye for
bread making is milled by a roller milling proce-
dure resembling that used for wheat milling.
Grinding changes the mechanical properties of
the various tissues of the grain. Pericarp, seed
coat, and aleurone layer are the main parts of
bran fraction produced during milling. The miller
separates the bran and the embryo from starchy
endosperm to produce a high yield of flour. The
toughness of the bran enables it largely to with-
stand the crushing and tearing that is required to
detach the endosperm from the bran.
Milling can also be used to enrich different grain
tissues, for example pericarp/testa, aleurone, and
endosperm. Milling rye in a roller mill produces as
many as 50 different mill streams varying in yield
percentage, gross chemical composition, and tech-
nological properties. For example, the viscosity and
dietary fiber characteristics are important for the
technological and nutritional properties (Glitsø
and Bach Knudsen1999). Analogously to wheat
bran, rye bran is a commercial milling product con-
taining the outer layers of the grain but more
endosperm than wheat bran. The dietary fiber con-
tent in 8 Nordic rye bran products varied from 41
to 48% of dry matter, starch content from 13 to
28%, and protein content from 14 to 18% (Kamal-
Eldin and others 2009).
Bread products: rye bread technology
Baking with rye is different from baking with
wheat in many respects. The main difference
between rye and wheat flours is that rye pro-
tein cannot form a continuous network and an
elastic dough. Instead rye pentosans (mainly
Table 4.4 Rye-based consumer products
Milling products Bread products Other rye products
Whole grain rye Rye bread Rye porridge
Steel cut rye Crispbread Berry pastries
Crushed rye grains Thin crispbread Karelian patries
Malted and crushed rye grains Rye rolls and buns “Kalakukko” – rye-dough-covered baked fish
containing fish, meat and /or vegetables
Precooked rye kernels Rolls, buns and breads containing
wheat/rye-mixture
“Mämmi” – Finnish Easter pudding
Malted rye kernels Parbaked rye product Rye pasta
Whole grain rye flour Rice-rye-mixture
Shifted rye flour
(variations is ash content)
Snack products
Rye bran Crispbread sandwich
Rye flakes Rye hamburger
Four-grain flakes with rye
Toasted rye flakes
Breakfast cereals (muesli, others)
Sourdough rye bred mix
CONSUMPTION AS FOOD 81
arabinoxylans) are able to bind water during
mixing to produce a dough that can be baked
into bread.
The most typical rye bread in Finland,
Denmark, Russia, and the Baltic countries is soft whole grain rye bread made by using a sourdough
method. In this method, the main ingredients –
whole grain rye flour, water, and starter culture
(usually seed from a previous sourdough batch
with stable microflora) – are mixed and fermented
for about 8–18 h. During the fermentation period
the lactic acid bacteria and the sourdough yeast
grow, and due to the microbial activity and the
enzymatic reactions of the microflora, flavor com-
pounds and flavor precursors such as amino acids
are formed. The main components formed are
lactic acid and acetic acid. After fermentation,
more flour, water, and other ingredients are mixed
with the sourdough to make a dough. The dough
is left to rise for a short period, after which the
breads are shaped, left to rise again, and baked.
Without sourdough, whole meal rye or wheat-
rye flour mixes are very difficult to process because
the acids and enzymes formed or activated during
fermentation modify the protein and pentosan
phases with positive effects on moisture, porosity,
and crumb elasticity. Sourdough also provides
an aromatic and pleasing flavor, and improves
overall quality and shelf-life. The positive influ-
ence of sours are based on the increased swell-
ing power of the pentosans and mucilages of rye
flour and a simultaneous inactivation of some
enzymes, particularly amylase (Brummer and
Lorenz 2003).
Whole meal rye doughs contain high amounts
of flour particles that have a high concentration
of cell walls. The cell wall material is largely
responsible for the water-binding capacity and
rheological properties of rye doughs. The struc-
ture of the cell walls and, for example, the effects
of preharvest sprouting on the composition of
the grain play an important role in determining
the baking quality of rye. Differences in rye raw
material and technological operations cause
structural alterations to the dough components.
Hydration and degradation of cell walls have
been found to have a noticeable effect on dough
rheology and change the baking behavior of the
dough and influence the structure of the bread
(Fabritius and others 1997; Autio and others
1998). The sourdough process is commonly used
in rye bread baking, and the acid conditions
greatly affect enzyme activities and starch gelat-
inization. Both the cell wall degrading enzymes
and α-amylase affect the baking properties of
rye doughs and the quality of breads. Dough
softening during fermentation has been shown
to be partly dependent on the swelling or frag-
mentation of cell walls induced by xylanase,
whereas during baking this softening is mainly
due to α-amylase.
The most important methods for determining
the baking quality of rye flour are the falling
number and the amylogram, which are both
related to α-amylase activity. Rye flour with a low
falling number gives soft, sticky dough and the
resulting bread is dough-like. Rye flour with a
high falling number yields rigid stable dough but
the resulting bread is dense and hard.
Another popular type of rye bread is crisp-bread, which has a long shelf-life due to its very
low water content. For the production of crisp-
bread, rye with a low amylase activity is required.
There are three types of rye crispbread: normal
yeast fermented, sourdough fermented, and
cold crispbread, which is baked without the
addition of yeast. Crispbread has a long shelf-
life due to its very low water content (5–7%).
Third type of rye bread is pumpernickel, which originates from Germany. It is produced
from whole meal rye flour with the sourdough
process. Crispbread is now produced in differ-
ent countries using many different recipes and
baking conditions. The baking temperature is
kept rather low (100–170 °C), and baking time
ranges from 10 to 36 h. Pumpernickel bread has
a very dark and dense crumb, highly aromatic,
bittersweet taste, and very long shelf-life. The
bittersweet taste of pumpernickel is due to the
acids that are formed in the sour fermentation
and the amylolysis of the starch during sour-
dough fermentation, proofing, and baking that
produces glucose, maltose, and dextrins (Pyler
1988; Seibel and Weipert 2001).
82 CH 4 RYE
Other rye products
In addition to breads and different types of
flours, there are many other uses for rye as food.
Rye porridge is traditionally made of rye flour,
but nowadays rye flakes are used for making
porridge. “Mämmi”, the Finnish Easter pudding,
is made of rye malt flour, sugar, and spices.
Different types of pies and pastries originate
from Karelia on the border of Finland and
Russia. A traditional Karelian pastry is made
with a very thin coating containing rye and
wheat flour. The filling is made of cooked
mashed potatoes, rice or barley pudding. New
products include the blend of white rice and pre-
cooked rye grains for use as an accompaniment,
pasta products that contain both wheat and rye,
instant rye flakes mixed with dry berries for
breakfast use, and snack products.
Flavor of rye grainThe characteristic intense flavor of rye products
is formed through the flavor components and
precursors of rye, but particularly through the
processing techniques used.
Chemical compounds influencing rye flavor
Volatile compounds may influence the perceived
flavor of rye, the dominant compounds being
aldehydes, ketones, and alcohols (Schieberle and
Grosch 1994; Hansen 1995; Grosch and Schieberle
1997; Kirchhoff and Schieberle 2002; Pozo-Bayón
and others 2006). Non-volatile compounds may
influence flavor directly, or indirectly as flavor
precursors through reactions that form new fla-
vor compounds. Phenolic compounds contribut-
ing the flavor are alkyl(en)resorcinols, lignans,
and phenolic acids (mainly ferulic acid, but also
sinapic, p-coumaric, and caffeic acids) (Andreasen
and others 2000a, 2000b; Heiniö and others
2008). Heat or microorganisms may decompose
the phenolic acids into compounds with an
intense flavor; for example ferulic acid is a source
of 2-methyl-4-vinylphenol, described as having a
burnt, tar-like flavor (Hansen 1995). At high tem-
peratures, free amino acids or small peptides and
free sugars are important flavor precursors that
form volatile compounds in the Maillard reac-
tion that affect flavor, such as pyrazines, pyrroles,
and furfurals, which often give a roasted note.
In addition, lipids influence the flavor, either as
hydroxy fatty acids resulting from the oxidation
of lipids, or as free fatty acids resulting from the
lipase-catalyzed hydrolytic oxidation of lipids.
All chemical compounds are not flavor-active;
however, the perception depends on the odor
and flavor thresholds and the relative amounts of
compounds in the product.
Flavor of native rye
The chemical composition of native rye grains
varies significantly depending on the environ-
ment, the genotype, and their interactions. The
components of the soil influence the amino acid,
lipid, and sugar composition of the grain, which
also indirectly influences the perceived flavor.
Thus, the effect of the season and the cultivation
area might be more dominant for flavor formation
than, for example, the rye cultivar. For example,
the nitrogen content of the soil greatly influences
the composition of amino acids, and thus the
protein composition of the grain. The season is a
dominant factor, especially for protein and fat
production. Different grain varieties have their
characteristic flavor; for example, the oat-like
flavor is milder than the rye-like flavor.
The flavor of native rye is relatively mild when
compared to the flavor of processed rye (Heiniö
and others 2003b). In mechanical milling frac-
tionation, the rye kernel is separated into
endosperm, shorts, and bran fractions, each hav-
ing a characteristic flavor. Between the very mild
tasting innermost endosperm of the grain and the
strong and bitter tasting bran, a rye-flavored frac-
tion without bitterness has been observed
(Heiniö and others 2003a). The phytochemicals
are mainly concentrated in the germ and
bran fraction of the kernel (Shewry and Bechtel
2001; Decker and others 2002), but the middle
SUMMARY 83
fraction also contains significant amounts of
bioactive compounds (Liukkonen and others
2003a, 2003b). One reason for the bitter taste of
rye was found to be the small molecular weight
peptides, as shown by using different hydrolytic
enzymes (Heiniö and others 2012). Enzymes
could possibly also be used to decrease the per-
ceived bitterness.
Flavor formation in processing of rye
The grain flavor is considerably modified by
several processing techniques, such as germina-
tion and subsequent drying, extrusion cooking,
autoclave, puffing and roasting techniques, or
microwave heating, which all have a high pro-
cessing temperature in common. In general, some
kind of processing is required for fine-tuning the
rye flavor and for achieving different types of rye
products (Hansen 1995; Schieberle 1996; Grosch
and Schieberle 1997; Heiniö 2003; Heiniö and
others 2003b).
Sourdough fermentation used in baking rye
bread is perceived as being intense and bitter in
flavor (Hellemann and others 1987, 1988; Heiniö
et al. 1997). Fermentation strengthens the sour,
rye-like flavor, and influences mainly the bread
crumb flavor, whereas baking results in a
roasted flavor. For consumers, the most domi-
nant sensory attribute of rye bread is its rye-
like flavor, but perceptions of sourness and
saltiness (which have been shown to compen-
sate each other) are substantially associated
with rye bread (Hellemann and others 1988;
Heiniö and others 1997). Salt-free bread has a
bland taste, and salt is used in foods for improv-
ing the taste, texture, and stability, and for
strengthening the flavor. The perceived sourness
of rye bread is shown to be strongly associated
with the concentration of lactic and acetic acids
(Hellemann and others 1988).
The oxidation of lipids and enzymatic and heat-
ing reactions are the key reactions influencing
flavor formation in rye bread (Schieberle 1996).
Volatile compounds evaporate from flour due to
oxidation reactions. Enzymatic reactions produce
flavor-active compounds during sourdough
fermentation and at the beginning of baking. The
enzymes may originate from the flour, from the
yeast or lactic acid bacteria, or from the additives.
The flavor compounds produced during the
baking process are possibly the most essential
compounds for the flavor of rye bread, and they
mainly form during the heat treatments, such as
the Maillard reaction and caramelization.
Germination is halted by a heat treatment, and
is thus very effective in modifying the cereal
flavor, resulting in a fresh, cereal-like, somewhat
roasted flavor and hard, crispy texture to rye
(Heiniö and others 2003b). Germinated grains
are also a good source of free amino acids and
sugars, which act as flavor precursors.
SummaryIn terms of total production (less than 1% of
world production) rye is a minor cereal. The
world rye production largely takes place in the
Northern part of the region from the Nordic Sea
to the Ural Mountains. In countries with a high
consumption of rye, the per capita consumption
is in the range of 10–30.
In contrast to wheat, rye is mostly consumed
as whole grain flour in breads and other cereal
products, which makes rye products a good
source of DF and micronutrients and bioactive
compounds such as phenolic compounds, vita-
mins, trace elements, and minerals.
Rye proteins, unlike wheat protein, cannot form
a continuous network and an elastic dough. Rye
pentosans (mainly arabinoxylans), however, are
able to bind water during mixing to produce a
dough that can be baked into bread. The flavor and
structure of rye bread are also quite different from
those of wheat bread, and they vary depending on
flour type, other raw materials and ingredients,
process, baking conditions, and time, as well as the
size and shape of the bread.
There has been much research data about the
health effects of rye in recent years, supporting
the bioavailability of many of the phytochemi-
cals, and demonstrating the favorable effects on
84 CH 4 RYE
glucose metabolism and the satiating effects of
rye bread, as well as its protective effects against
certain cancers. There is thus a good reason to
work for an increased use of whole meal rye flour
in various bakery products as well as in mixed-
flour products. This demands that processing is
developed that takes into account the sensory
demands of the modern consumer.
AcknowledgmentsKaisa Poutanen is grateful for funding from the
Academy of Finland.
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