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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