Cereal_grains_for_the_food_and_beverage_industries_2075944_z_lib

6

Rye

DOI: 10.1533/9780857098924.220

Abstract: Rye (Secale cereale) has been cultivated in Europe since ancient times
and is genetically related to wheat and barley. Representing less than 1 % of the
world cereal production, rye is mainly grown where rye breads are most popular;
in countries such as Poland, Germany and Western Russia. Despite the agronomic
advantage of being able to flourish in conditions which are unsuitable for wheat,
rye’s bread-making performance is markedly lower in comparison. The
macronutrients in rye are the same as other cereals – starch, dietary fibre and
protein. However, rye generally contains less starch and crude protein than wheat,
but more free sugars and dietary fibre. Of the free sugars, sucrose dominates. The
rye grain is second after wheat in importance for the production of breads (black
bread, crisp bread, pumpernickel and sourdough bread), and it is also important
in the distillation of rye whisky and as livestock feeds.

Key words: rye, chemical composition, rye utilization in food and beverages.

6.1 Introduction

Rye (Secale cereale) has been cultivated in Europe since ancient times and
is genetically related to wheat and barley. It shares common origin with
other species of the tribe Tricaceae (wheat and barley) in South Western
Asia (Ma et al., 2004), where it is supposed to have evolved from its ances-
tor Secale montanum, a wild species found in the Black and Caspian Sea
areas. However, rye’s primary centre of origin is not precisely known. Both
rye and oats may have originated as weed species in wheat and barley crops.
From an agronomical standpoint, rye is considerably more winter hardy
than wheat and produces economically viable yields on poor, sandy soils
where other crops fail to grow. It is also a good rotation crop because of its
ability to compete effectively with weeds, and in some countries rye is used
as pioneer crop to improve the fertility of wasteland and sterile soils. Rye
is also more resistant than wheat to many pests and diseases, although it is
more susceptible to attack by ergot (Claviceps porpurea). Rye accounts for
only 1 % of total world cereal production because it is generally related to
local food production or on-farm use. It is grown globally, but its cultivation

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Rye 221

is predominately concentrated in Poland, Germany, western Russia and
Ukraine where rye breads are most popular.

Rye is characterized by high levels of lysine and hemicelluloses such as
pentosans compared to wheat, thus significantly influencing the functional
properties of rye flour in bread-making. In more detail, hemicelluloses
prevent protein aggregation into gluten which is required for the develop-
ment of the visco-elastic properties of wheat bread dough.

The rye grain ranks second in importance after wheat for the production
of breads (black bread, crisp bread, pumpernickel and sourdough bread),
and it is also important in the distillation of rye whisky and as livestock
feeds. Rye grain is frequently contaminated with ergot bodies, sclerotia of
the fungus C. porpurea (Fr.) Tul. ergot is a mycotoxigenic contaminant
which, when consumed in high quantities, is teratoxigenic and so can cause
abortion in livestock and also gangrenous ergotism This disease was known
as ‘holy fire’ or ‘St Anthony’s fire’ in the 11th to 16th centuries, although its
connection with ergot was not known at this time. The fungus Claviceps
infects the flower of the rye plant and, during seed development, the whole
rye kernel in the head of the plant is replaced with a dense mass of fungal
mycelium. When dried, the sclerotia of Claviceps are dull grey or purple-
black in colour. The alkaloids (ergotoxine and ergotamine) contained in the
ergot sclerotia cause hallucinations, agitation and other symptoms associ-
ated with ‘St Anthony’s Fire’ (Matz, 1991).

6.1.1 Production area, price and yield
It is likely that rye was more recently domesticated than other cereals,
although it was already known to the ancient Greek and Roman civiliza-
tions. Cultivation of rye migrated into Northern Europe, possibly northward
via Russia in the first millennium BC (Bushuk, 2001a). Another possible
route of migration is from Turkey across the Balkan peninsula to North–
Central Europe (Popov, 1939). From the latter, rye was brought to North
America and to South-West America by European settlers during the six-
teenth and seventeenth centuries (Bushuk, 2001a). During this same period,
rye cultivation spread eastward in Europe to Siberia. Its cultivation was also
introduced in Argentina, Australia and South Africa during the nineteenth
and twentieth centuries. Nowadays, rye cultivation is concentrated in Poland,
Germany and Western Russia (Table 6.1).

World rye production has fallen gradually from 33 million tonnes during
the period 1961–1966 to slightly more than 12 million tonnes in 2010 (FAO/
UN, 2012). The decline in total production has been greatest in the former
Soviet Union and Poland where wheat and barley have taken the place of
rye (Tables 6.1 and 6.2). A decline of 82 % (from 30 to 5.3 million hectares)
of the world rye harvest area from 1961–2010 is matched by a world produc-
tion reduction of 65 % (from 35 to 12 million tonnes) (Tables 6.1 and 6.2).
However, from a yield standpoint, the productivity of rye grain has more

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222 Cereal grains for the food and beverage industries

Table 6.1 Production (in thousands of tonnes from 1961–2010) of rye, oats, barley
and wheat for country producing significant quantities of rye

Country Rye Oats Barley Wheat
1961 2010 1961 2010 1961 2010 1961 2010

Albania 7 2 12 27 9 7 98 295
Argentina 510 44 700 660 800 2983 5725 14 915
Australia 11 33 1000 1374 941 7294 6727 22 138
Austria 472 164 335 98 511 778 712
Belgium- 130 2 514 25 427 373 787 1518
1850
Luxembourg 17 3 21 395 24 279 545
Brazil 70 18 207 40 611 833 2040 6171
Bulgaria 166 216 4379 2298 2452 7605 7713 3995
Canada 5 5 101 381 72 78 1030 23 167
Chile 1300 650 1100 600 3710 2520 14 294 1524
China 994 118 959 138 1580 1585 1666 115 181
Czechoslovakia 514 255 683 274 2808 2981 434 4162
Denmark 4 0 1 70 19 5060
Ecuador 127 69 1 810 365 1340 78
Finland 347 151 941 448 5413 10 102 461 8
France 4019 2903 2591 600 3669 10 412 9573 724
Germany 22 35 2769 116 221 318 5076 40 787
Greece 310 79 144 123 984 966 1527 24 107
Hungary 1 0 152 148 515 1223 1935 1600
Ireland 96 14 381 0 278 991 470 3764
Italy 2 0 279 1976 161 8301 669
Japan 1 3 1 37 571 2566 1781 6850
Morocco 301 10 585 385 204 720 571
Netherlands 3 32 8 427 528 482 4876
Norway 1 0 14 292 216 216 1370
Peru 8356 3270 593 11 1339 3533 27 293
Poland 119 18 174 1334 52 75 153 219
Portugal 20 0 66 1662 81 2792 9488
Republic of 2 430 83
104 34 2940 0 468 1311 172 39
Korea 9 2 36 194
Romania 65 304 3990 5812
South Africa 351 252 275 34 1744 8157 871 1430
Spain 169 123 945 1228 5611
Sweden 34 14 118 1018 92 174 3438 2184
Switzerland 570 366 495 563 294 7240 839 524
Turkey 18 38 1394 5053 5252 316 19 660
UK 694 189 47 9 8546 3925 14 878
USA 15 044 4333 204 12 271 8350 – 60 062
USSR/Russian 3 685 7135 41 508
35 109 12 373 1862 1178 72 411 123 544 2614
Federation 14 665 3220 33 539 653 654
World
64 19 622 222 357
437

49 589

Source: Data from FAO/UN (2012).

© Woodhead Publishing Limited, 2013

Table 6.2 Producer prices (US $/tonne) of rye from 2000–2009

Crop years

Countries 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009

© Woodhead Publishing Limited, 2013 Albania 208.8 209.1 214 246.2 340.5 340.4 357 354.1 417.2 368.9
Armenia 173.5 162.4 143.7 152.1 224.9 253.5 281.9 357.1 434.7 254.2
Austria 100 90.4 86.6 121.9 98.2 98.4 146.9 242.6 194.8 112.5
Azerbaijan 101 69.4 80 94.9 103.7 103.1 126.2 139.7 157 172.8
Belarus 99.7 74.7 66.1 57.5 67.8 68.4 72.6 88 129.2 90.6
Belgium 84.7 85.2 73.4 123 93.2 107.1 109.2 122.5 140.8 90.8
Bolivia (Plurinational 143.8 134.7 124.1 117.7 114.9 114.8 114.1 121.3 162.6 169.3

State of) 128.7 127.6 135.8 170.9 195.6 166.9 196.5 220.8 471.5 340
Bosnia and
85.2 72.1 54.1 56.2 53.4 54.3 59.4 70.4 90.9 74.4
Herzegovina 83.8 83.8 77 109.7 144.3 98 104.6 178 255.8 202.9
Brazil 47.1 62 85.4 94.2 100.9 95.8 88.2 135.6 243.7 153.2
Bulgaria 497.1 469.5 235.5 344.4 305.5 304.7 406.1 476.9 639.4 805.3
Canada 122.5 119.9 140.8 150.2 158 124.6 161.2 205.7 292.4 209.9
China 70.2 100 113 124.8 137.1 98.5 126.4 216.9 280.5 139.7
Croatia 101.4 91.4 85.2 101.4 119.1 116.3 126.4 217.6 255 136.4
Czech Republic 72.7 78.7 84.9 79.7 138.7 110.3 156.4 239.6 153.9 104.4
Denmark 120.7 117.5 119.5 141.1 150.4 147 175.8 263.2 303.2 186.1
Estonia 94.2 93.4 89.9 120.5 115 115.1 147.8 258.5 218.3 143.3
Finland 96.4 87.3 80.9 110.6 135.5 98.4 126.8 228.9 219.7 118.1
France 126 119.5 146.7 128.1 149.5 150.7 260.4 234.4 180.6
Germany 92.8 71 78.5 116.4 110.2 87.5 95.7 224 177.9 120.1
Greece 114.2 114.1 120.3 143.8 165.5 159.5 151.9 209.7
Hungary 64.4 63.4 59.6 83 92.3 96.2 99.3 151.7 –
Italy 65.4 42 61.4 50.4 145 156.2 164.4 165.6 202.3 143.8
Kazakhstan 94 84.4 46.9 103.2 112.9 94 119.7 224.1 174.7 172.6
Kyrgyzstan 82.3 86.8 93.8 97.4 111.2 104.7 136.7 223.8 195.6 112
Latvia 92.2 99.9
Lithuania
(Continued)

Table 6.2 Continued

Crop years

Countries

2000 2001 2002 2003 2004 2005 2006 2007 2008 2009

© Woodhead Publishing Limited, 2013 Luxembourg 87.9 90.6 75.3 108.2 103.7 104.4 127.1 265.1 146.5 99.9
Mexico 153.3 155.2 362.5 148.3 141.8 275.4 229.5 201.3 269.5 222.4
Morocco 362.2 311.4 252.4 265.8 294.7 294.9 303.7 331.6 420.5
Netherlands 93.2 91.4 81.9 110 110.7 105.9 136.9 228.2 186 –
Norway 222.2 210.8 258 296.3 285.6 282.8 293.7 318 349.3 –
Peru 149 151.1 153.6 149.5 269.7 163.9 201.6 179.1 314.6 331.5
Poland 83.1 89.2 81.4 90.8 96.7 85.4 124.2 218.3 214.6 221.6
Portugal 101.1 102.6 114.8 146.7 161.6 149.5 150.7 219.3 283.7 105.5
Republic of Moldova 100.9 82.3 59.4 106.8 111.8 92.1 98.8 169.2 216.4 184
Romania 121.7 106.7 83.3 151.4 138.1 107 111.2 193 227.5 –
Russian Federation 64.4 40.3 44 87.1 83 91 140.3 176.3 –
Serbia and Montenegro 70.8 113.7 137.2 155.8 217.5 120.4 120.5
Slovakia 173.4 89.7 93.6 115.4 125.1 121.8 135 218.3 214 218.5
Slovenia 86.6 112.9 126.8 148.1 152.6 115.2 135.4 265.1 242.9 162.3
South Africa 109 110.6 88.2 132.2 148.2 132.5 132.4 158.3 152.9 221.9
Spain 100.9 110.4 114.8 161.4 154.2 163.2 157.7 243.8 234.8 –
Sweden 104.1 91.5 90.9 112.9 118 121.2 139.5 277.4 212.4 169.2
Switzerland 99.4 268.4 288.1 355.7 307.6 333.9 344.8 415.3 446.9 106.4
The former Yugoslav 337.5 148.1 149.3 178.2 215.1 162.8 158 435.9 560.8 316.7
151.7 352.4
Republic of 89.6 112.1 148.9 191.7 201 182.6 238.8 305.9
Macedonia 114.1 63.7 42.8 79.7 74.1 61.9 81.8 166.9 154.4 241.3
Turkey 86.2 93.6 83.9 88.2 107.3 92.7 104.7 133.3 140.6 78.9
Ukraine 105.9 113 131 115 127 130 131 197 249
UK 102 117.7796 116.7625 135.5878 150.8673 142.0449 157.7104 224.1208 253.5468 –
USA 126.2612 194
World average price 191.6381

Source: Data from FAO/UN (2012).

Rye 225

than doubled during the period 1961–2010, from 1.16 tonnes/ha to 2.4
tonnes/ha. This is mainly due to advances in agronomic techniques and the
advent of chemical fertilization. In 2010, the rye yields of the three principal
producing countries, Russian Federation, Poland and Germany, were 1.19,
2.34 and 4.63 tonnes/ha, respectively. The highest yields recorded in 2010
were reached by Uzbekistan with 6.6 tonnes/ha (FAO/UN, 2012).

The producer price evolution (from 2000–2009) of rye, expressed
US $/tonne, is reported in Table 6.2. High variability, in terms of the pro-
ducer price, can be observed amongst the production countries. Generally,
the world rye grain price increased 1.5-fold over the last 10 years, moving
from 126 US $/tonne in 2000 to 191 US $/tonne in 2009 (Table 6.2). Over
the last 10 years, China always showed the highest producer price, equal to
448 US $/tonne, among the rye producer countries (FAO/UN, 2012).

6.1.2 Phytology, classification and cultivation
Rye is a plant belonging to the grass family, Gramineae, and the genus S.
cereale L. (diploid type) is the most extensively cultivated. Artificially pro-
duced tetraploid rye (2n = 14), with a double number of chromosomes, has
been unproductive due to its higher sensitivity to ergot infection and cold
climates and, thus, it is only grown to a limited extent in Europe.The produc-
tion of inbred lines with resistance to ergot is necessary for successful hybrid
rye breeding. In rye, the absence of physiological resistance to ergot has
ruled out breeding for ergot resistance (Wolski and Pietrusiak, 1995). The
most relevant effort in rye breeding has been localized in North-Western
Europe where about 95 % of rye is produced (Lampinen, 1995). Important
improvements have been made in seed size, winter hardness, grain yield,
plant height, lodging resistance and intrinsic quality. Major rye-breeding
programmes are underway in Germany (Stuttgart); however, grain yield, not
ergot resistance, is the main breeding objective (Bushuk, 2004).

Most rye is grown as an autumn-sown annual crop, like winter wheat,
and is generally called ‘winter rye’. Because of its greater cold temperature
resistance, winter rye can be successfully cultivated in areas where the
climate is too severe for other winter cereals such as wheat and barley
(Bushuk, 2001b). Rye winter hardiness is a consequence of its low heat
requirements. In fact, it can survive temperatures of −25 to −35 °C, even
without snow protection, due to the structural rearrangements of certain
proteins during cold exposure. In particular, the glycoprotein content in the
crown of the plant works as a protective agent towards the cytoplasm and
the plasma membranes, thus protecting rye from destruction by freezing
(Bushuk, 2001b).

Rye is a vigorously growing hardy plant and is drought tolerant due to
its high efficiency in water-use (Listowsky, 1960). In fact, under conditions
of water deficiency, rye plants exhibit some xeromorphic characters such as
smaller, greener leaves and a thick cuticle layer, which are helpful in the

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226 Cereal grains for the food and beverage industries

5 kV ×18 1 mm AMRF, UCC

Fig. 6.1 Scanning electron microscope (SEM) micrograph of longitudinal section
of rye kernel.

economical use of water (Bushuk, 2001b). Additionally, the rye root system
is well developed and extensive, facilitating the access to water sources and
soil nutrients, especially those which are deeply embedded. Therefore, soil
humidity/fertility requirements of rye are the lowest among the cereals.
However, despite rye’s relatively high drought tolerance, there are signifi-
cant differences between levels of tolerance of different rye cultivars (Grze-
siuk, 1979). Rye performs better than wheat in light soils and can tolerate
higher levels of aluminium and low pH. Rye is cultivated successfully above
the Arctic circle in Scandinavia, close to the Antarctic circle in Chile, and
at altitudes of 4300 m in the Himalayas (Matz, 1991).

6.1.3 Structure of the rye kernel
The rye caryopsis is arranged in pairs alternately on a zigzag shaped rachis
and is harvested free of the surrounding lemma, palea and outer glumes.
The rye kernel is more slender, pointed and longer than those of wheat and
barley (4.5/10–1.5/3.5 m) (Fig. 6.1) and the surface is often wrinkled.As with
wheat, a crease extends the full length of the ventral side of the grain. Rye
grains (Fig. 6.2) are normally greyish-yellow in colour, but this can vary
within an individual variety and even within the same sample. The colour
variation depends on the region of cultivation and harvest conditions. Rye
kernels are composed of three main parts – bran, endosperm and germ (Fig.
6.3). The starchy endosperm accounts for 86.5 % of the kernel, bran (peri-
carp and testa) makes up 10 %, and the germ (embryo and scutellum)
represents 3.5 % of the grain (Bushuk, 2004). The starchy endosperm of the
rye grain is softer than that of wheat (durum and soft wheat); thus, the floury
contents of the rye kernels are readily released upon milling.

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Rye 227

Fig. 6.2 Rye grains.

Brush Crease

Central endosperm Cuticle
Prismatic endosperm Epidermis
Peripheral endosperm

Aleurone cells
Scutellum
Coleoptile
Plumule

Root

0.5 mm Sheath and cap
(a)
(b)

Fig. 6.3 Longitudinal section (a) and transverse mid-section (b) of rye kernel.

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228 Cereal grains for the food and beverage industries

The anatomy of the rye caryopsis is illustrated in Fig. 6.3. The caryopsis
is similar in appearance to the other common cereals such as wheat and
barley. The seed consists of an embryo attached, through the scutellum, to
the starchy endosperm and aleurone tissues. The endosperm and aleurone
are enclosed by the remnants of the nucellar epidermis and seed coat. The
latter surrounds the whole kernel and adheres closely to it.

Rye caryopsis is covered with the brush (or hair-like protuberances)
located mostly at the distal end of the kernel (Fig. 6.3). Starting from the
outside of the caryopsis, the bran layers, and in particular the aleurone, are
rich in vitamins, minerals and phytate compounds (Bushuk, 2001b).

The bran layers consist of the pericarp, seed coat, the nucellus, the aleu-
rone layer and a large portion of subaleurone starchy endosperm (Fig. 6.3).
Pericarp is the ripened ovary wall that surrounds the kernel, and just inside
it is the seed coat which represents a thin, strong layer lying between the
pericarp and the nucellus. The seed coat forms a waxy, water-resistant layer
that surrounds most of the kernel, leaving only a small region at the base
of the grain susceptible to water penetration.

The nucellus is located between the endosperm on the interior and the
seed coat on the exterior, and is intimately associated with both tissues.
Endosperm tissue is surrounded by aleurone cells that form a continuous
thick layer. These are morphologically distinct from the starchy endosperm
cells and represent the only living endosperm tissue. The aleurone layer is
rich in proteins, minerals and vitamins, especially B vitamins, and is difficult
to separate from the bran (Clydesdale, 1994). Inside the aleurone layer lies
the starchy endosperm that represents the most predominant organelle of
the mature rye kernel, as in all of the cereal grains, and may account for
about 80 % of its total weight (Bushuk, 2001b). It is composed of three types
of cells – subaleurone (peripheral) tissue, prismatic cells and central endo-
sperm cells (Fig. 6.3).

The sub-aleurone tissue is formed by isodiametric cells, represents the
youngest part of the starchy endosperm (Shewry and Bechtel, 2001), and is
typically characterized by large amounts of storage protein. Prismatic cells
represent the major part of the starchy endosperm and contain large quanti-
ties of starch granules. The central endosperm cells are irregular in shape,
variable in size (Shewry and Bechtel, 2001) and represent the oldest part
of the starchy endosperm.

The rye endosperm is the primary storage site of protein and starch gran-
ules. Starchy granules are present in two major size classes (types A and B).
Type A granules have diameters up to about 35 μm while the smaller and
spherical type B granules have diameters generally less than 10 μm (see Plate
VI in the colour section between pages 230 and 231).The other major reserve
is the spherical protein bodies that vary in diameter from about 0.1 to 1 μm
(Plate VI) and surround the starch granules, similar to wheat and barley.

The rye germ, or botanically speaking the embryo, lies on the lower
dorsal side of the kernel. From a chemical point of view, the rye

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Rye 229

Table 6.3 Proximate composition of rye and other cereal grains

Component Rye Triticale Wheat Barley Corn Oats Rice

Carbohydrates 80.1 78.6 78.9 75.7 81.2 66.0 86.8
Proteins 13.4 14.8 14.3 13.1 10.4 13.0 9.4
Lipids 1.8 1.5 1.9 2.1 4.5 5.5 1.8
Crude fibres 2.6 3.1 2.9 6.0 2.4 11.8 0.9
Ash 2.1 2.0 2.0 3.1 1.5 3.7 1.1

Source: Based on data of Bushuk (2004).

germ contains high levels of proteins and lipids but very little starch. It
is formed by the embryonic axis and the scutellum and represents a
viable structure capable of metabolic activity (Fig. 6.3) (Shewry and Bechtel,
2001). The scutellum is a shield-shaped structure that separates the embry-
onic axis from the starchy endosperm and functions as a food reserve
for the embryo early in germination (Bushuk, 2001b). As in other cereals,
the embryonic axis is composed of the shoot, the mesocotyl and the radicle
(Fig. 6.3).

6.2 Chemical constituents of the rye kernel

The proximate composition of the rye kernel (Table 6.3) is typical of a
cereal grain with carbohydrates being the main constituents and accounting
for approximately 70 % of the grain (Bushuk, 2004). As in wheat and barley,
starch is stored in the endosperm and represents the major carbohydrate
component. Rye generally contains less starch and crude protein than
wheat, but more free sugar and dietary fibre. Of the free sugars, sucrose
dominates. Protein contents in rye are similar to those of wheat, although,
in both cases, there are considerable variations (around 8–15 %), depending
mainly on growth conditions (Wrigley and Bushuk, 2010). Values of lipids
(1.8 %), crude fibre (2.6 %) and ash (2.1 %) (Miller, 1958) are also similar
to those of wheat and triticale (Shewry and Bechtel, 2001).

The mineral content is particularly high in the aleurone layer, due to the
presence of phytin granules which are made up mostly of the potassium
and magnesium salts of myoinisitol hexaphosphate. As in other cereals,
phosphorus, potassium, calcium and magnesium are the major minerals
(Bushuk, 2001b).

6.2.1 Carbohydrates
The carbohydrate components of the grain can be divided into starch and
non-starch polysaccharides. Starch represents the major storage reserve in
the endosperm. As in wheat and barley, starch granules in rye appear to fall

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230 Cereal grains for the food and beverage industries

into two classes, depending on shape and size. There is a high proportion
by weight of A-granules (15–35 μm in diameter with lenticular shape)
whose formation was initiated early in endosperm development and
increases in size during maturation. The small B-granules (diameter less
than 10 μm and approximately spherical in shape) are vastly more
numerous than the large granules, accounting for 36 % of the total starch
weight at maturity (Karlsson et al., 1983) and accumulating relatively
late in the grain development (Verwimp et al., 2004). The rye starch
structure and properties are comparable to those of other cereal
starches. The starch structure consists of amylose and amylopectin, with
amylose representing approximately 24–26 % of the total starch (Berry
et al., 1971).

The birefringence end-point and gelatinization temperature ranges of
rye starch granules have been reported to be comparable to those of con-
ventional wheat starch (Sharma et al., 2002). However, the starch properties
of rye are influenced by growth environment, harvest year and, to a lesser
extent, genotype (Hansen et al., 2004).

6.2.2 Dietary fibre
The dietary fibre of rye represents about 17 % of the whole grain, of which
approximately 4 % is soluble fibre (Shewry and Bechtel, 2001). The compo-
nents of this fraction are pentosans, β-glucan, lignin, cellulose and arabin-
oxylans (Shewry and Bechtel, 2001). Vink and Delcour (1996) reported that
a rye grain with 16.5 % dietary fibre contained 2.3 % β-glucan, 2.6 % cel-
lulose, 3 % lignin and 7.6 % arabinoxylan. The dietary fibre content and, in
particular, the pentosan content, largely influence the water-absorbing
properties of rye flour and are functionally more important than the protein
in determining bread quality. Rye arabinoxylans and pentosans show high
water-binding capacities (0.47 g/g dry matter) and form highly viscous solu-
tions. This behaviour influences the milling and technological properties of
the grain and its other components, such as starch and protein (Vink and
Delcour, 1996).

The high water-binding capability of rye may also contribute to the poor
dough properties of rye, including stickiness, via interactions with the gluten
proteins (Dhaliwal et al., 1988).

Although rye pentosans are a minor component of grain (between 7 and
9 %), they drastically influence its baking performance. Moreover, the
amount of water-extractable pentosans must be considered in addition to
their state and condition. Indeed, they represent the major source of water-
binding capacity for dough, due to their extremely viscous but low tensile–
elastic properties (Hoseney, 1984) producing a film inside the vacuoles of
the fermenting dough, contributing to gas retention and, thus, to the bake
volume of the resultant bread. Rye pentosan water-binding capacity has

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Rye 231

been identified as a factor that positively influences freshness, shelf-life and
starch retrogradation (Delcour, 1995). However, the hardness of wholemeal
rye bread seems to be influenced by the level of fibre, and soluble pentosans.
Decline of bread texture is observed in the presence of extractable pento-
sans with high molecular weights (Buksa et al., 2010)

Even though the pentosan content in the rye endosperm is lower than
those of the external parts of the kernel, the latter are more readily water-
extractable. Thus, the water-extractable amount of pentosans in ‘white’ flour
is about 40 % greater than in the whole kernel. This ensures a better baking
performance of flour than of meal (Bushuk, 2001b).

6.2.3 Protein
The protein content of the rye kernel ranges from 6.5 to 14.5 % and is
dependent on the crop growth conditions, although the grain protein
content has also been reported to be primarily influenced by genotype
(Hansen et al., 2004). The storage protein in the rye endosperm is classified
as forming gluten and its content is reported to be higher than wheat flour.
However, the resulting dough resistance to stretching is less than that con-
ferred by wheat gluten because of a lack of cohesiveness of rye gluten due
to prolamins called ‘secalins’ (Chen and Bushuk, 1970). As a consequence,
the processing of rye dough is more difficult than for wheat dough due to
its stickiness. The resulting baked rye loaf is lower in volume, with a coarser
crumb structure, but the distinctive flavour of rye makes it especially attrac-
tive to many customers.

Rye protein can be conventionally classified into three broad groups. The
first includes the storage proteins localized in the starchy endosperm which
are mainly prolamins, called ‘secalins’. These storage proteins function only
as nitrogen, sulphur and carbon stores for germination and seedling growth.
The second group is the hydrolytic enzymes implicated in storage com-
pound mobilization and their specific inhibitors. The third group includes
proteins potentially involved in pest and pathogen control by functioning
as toxins and/or inhibitors (Bushuk, 2001b). The rye gluten is considered to
be sufficiently similar to that of wheat from a coeliac disease toxicity point
of view (Wieser and Koehler, 2008). However, from a nutritional approach,
rye proteins are recognized to be superior to those of wheat and other
cereal grains because of their better balance of essential amino acids. This
is essentially due to the greater amount of lysine (21.2 g/100 g total nitro-
gen) (Table 6.4) (FAO, 1970; Hulse and Laing, 1974) and the fact that it is
mainly concentrated in the bran and germ fractions. In spite of the higher
content of lysine in rye, this amino acid is still the nutritionally limiting
amino acid in rye, as in wheat (17.9 g/100 g total N; range 13.1–24.9) (Seibel
and Weipert, 2001a) and other cereal grains. The amino acid profile of rye
is compared to other grains in Table 6.4.

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232 Cereal grains for the food and beverage industries

Table 6.4 Range of amino acid content of rye

Amino acid (g/100 g total nitrogen) Wholemeal rye

Alanine 23.5–30.2
Arginine 18.4–34.4
Aspartic acid 38.5–51.1
Cysteine
Glutamic acid 8.5–15.6
Glycine 135.6–167.6
Histidine 30.2–35.0
Isoleucine 12.5–16.5
Leucine 20.0–24.2
Lysine 36.1–40.6
Methionine 15.1–28.1
Phenylalanine
Proline 5.9–18.1
Serine 25.0–30.0
Threonine 51.7–73.8
Tryptophan 25.0–30.6
Tyrosine 19.1–23.1
Valine 3.4–8.8
7.6–17.5
20.6–34.3

Source: Data from FAO (1970) via Hulse and Laing (1974).

6.2.4 Lipids
There is approximately 1.5–2.0 % (dried weight) lipid in rye, which is similar
to that of wheat, barley and triticale, but considerably lower than the lipid
content of oats. Unlike other cereals, rye lipids have a slightly greater pro-
portion of the highly unsaturated linoleic acid (55.6 % – C18:2). This rep-
resents a limiting factor for the storage of rye due to its high susceptibility
to oxidation and, thus, rancidity.The content of other fatty acids are reported
as being 16.5 % palmitic acid (C16:0), 0.6 % stearic acid (C18:0), 15.6 %
oleic acid (C18:1), 10.4 % linolenic acid (C18:3) and 1.3 % eicosenoic acid
(C20:1) (Hulse and Laing, 1974).

Lipids are also present throughout the starch granules in the starchy
endosperm in amounts proportional to the amylose content. The starch
lipids of rye mainly comprise free fatty acid (FFA) (palmitic acid 23 %, oleic
acid 41 % and linoleic acid 35 %) and lysophosphatidylcholine (LPC) con-
taining 46 % palmitic acid, 1 % stearic acid, 42 % oleic acid and 10 % linoleic
acid (Acker and Becker, 1972).

6.2.5 Minerals
The ash content in rye grain typically reaches a concentration of 2.1 %
which is comparable to wheat. The ash content is particularly high in the
aleurone layer which contains the phytin granules and a mixture of the

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Table 6.5 Mineral and vitamins composition of rye
and wheat grains

Constituent (mg/100 g dw) Rye Wheat

Minerals 380 410
Phosphorus 520 580
Potassium 60
Calcium 70 180
Magnesium 130
Iron 6.0
Copper 9.0 0.8
Manganese 0.9 5.5
7.5
Vitamins 0.55
B-vitamins 0.44 0.13
Thiamin 0.18 6.4
Riboflavin 1.50 1.36
Nicotinic acid 0.77 0.53
Pantothenic acid 0.33 0
Pyridoxine 0
Carotene

Source: Data from Miller (1958).

potassium and magnesium salts of myoinositol hexaphosphate (Miller,
1958; Pomeranz, 1973) (Table 6.5).

6.2.6 Vitamins
Rye is reported to be a good source of thiamine, nicotinic acid, riboflavin,
pyridoxine, phanthotenic acid and tocopherol (Table 6.5). These are mostly
localized in the outer tissues of the rye grain and are removed during the
milling process. This is because they are stored principally in the germ and
aleurone layers of the grain (Bushuk, 2004).

6.2.7 Antinutritional factors
Rye grain contains some constituents that exert antinutritional effects, espe-
cially when used as whole grain in animal feed. The aleurone cells of the
rye grains are rich in phytic acid, present in phytin granules as potassium
and magnesium salts (Shewry and Bechtel, 2001), which bind calcium, zinc,
iron and magnesium. This prevents their absorption in the mammalian
digestive tract.

Other antinutritional compounds include trypsin inhibitor, which inter-
feres with the digestion of proteins, soluble hemicelluloses, which interfere
with feed digestion in monogastric animals, and alkyl resorcinols, a group
of phenolic compounds which are considered to be responsible for lowering

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234 Cereal grains for the food and beverage industries

feed intake, feed conversion efficacy and growth rate in animals (Bushuk,
2001a; 2004). However, a wide range of activities, including antimicrobial,
antiparasitic, antitumour and antioxidant effects, are attributed to rye grains
(Kamal-Eldin et al., 2001; Ross et al., 2001; Zhu et al., 2011).

6.2.8 Potential health effects of rye constituents
Rye contains important dietary fibre components (arabinoxylans, β-glucan,
lignans) combined with other bioactive compounds which have numerous
beneficial effects on human health (Aman et al., 1997). Rye fibre increases
faecal volume and reduces intestinal transit time, thus promoting proper
bowel function and preventing constipation (Gråsten et al., 2000, 2007;
Hongisto et al., 2006; Isaksson et al., 2008, 2009; Holma et al., 2010). More-
over, rye arabinoxylan, possibly β-glucan, and lignan have favourable effects
on cholesterol levels and on insulin and glucose metabolism, e.g. by increas-
ing the insulin sensitivity (Sandman et al., 1983; Hagander, 1987; Lund et al.,
1993; Zhang et al., 1993; Pietinen et al., 1996; Hallmans et al., 1997, 2003;
Davies et al., 1999, Leinonen et al., 1999, 2000; Gråsten et al., 2000; Mutanen
et al., 2000; Bondia-Pons et al., 2009; Rosen et al., 2009). Although compre-
hensive results on human intervention studies are scarce, it is difficult to
formulate any conclusion indicating that whole-grain rye is cancer-
protective. However, some epidemiological studies indicate that rye may
play this role (Landström et al., 1998; Kurtz and Zhang, 2001; Bylund et al.,
2003; Adlercreutz, 2010; Landberg et al., 2010). A summary of the potential
health effects of rye constituents is presented in Table 6.6.

6.3 Rye milling and applications in foods and beverages

Rye can be milled into flour and has a number of food and beverage uses
such as baked products and breakfast cereals and rye beers and whiskies.

6.3.1 Milling
To facilitate marketing and processing, rye grain is graded and, subsequently,
separated into parcels of relatively uniform properties. In Germany, North
America and Canada, where rye grading exists, the process is based on the
presence of foreign contaminants (with emphasis on ergot contamination)
and on physical characteristics, such as hectolitre weight and moisture
content. The number of grades of milling rye varies between countries.
Germany has one grade, Canada has three, and the USA has five grades
defined by the United States Standards for Rye and is currently used by the
Federal Grain Inspection Service (FGIS, 1993) (Matz, 1991; Bushuk, 2004).

The rye grain milling process is similar to that described for wheat,
although some important differences exist between the two cereals. In order

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Rye 235

Table 6.6 Potential health effects of rye and some of its components

Potential health effects References

Preventive effect on constipation due to the: increased Sandman et al., 1983
faecal weight; shorter intestinal transit time; softer Holma et al., 2010
faeces Hongisto et al., 2006
Hagander et al., 1987
Beneficial effect on weight control due to the increased Isaksson et al., 2009
viscosity of food in the stomach, thus delaying the Isaksson et al., 2008
evacuation of stomach contents into the small
intestine. This increases the replete feeling, and thus Gråsten et al., 2000
helps in dieting. Gråsten et al., 2007

Improved bowel function Leinonen et al., 1999
Decreased concentrations of some compounds that are Rosen et al., 2009
Lund et al., 1993
putative colon cancer risk markers Hallmans et al., 1997
Decreased postprandial insulin response Zhang et al., 1993
Leinonen et al., 2000
Reduced serum cholesterol due to reduced absorption Pietinen et al., 1996
of bile acids and cholesterol
Davies et al., 1999
Inverse association between the amount of dietary fibre Mutanen et al., 2000
in the diet and coronary heart disease Landberg et al., 2010
Zhu et al., 2011
Potential cancer-protective Adlercreutz, 2010
Bylund et al., 2003

to prepare rye grain for milling, it is subjected to a cleaning process aimed
at the removal of all undesirable materials using special machines, such as
milling separator, magnet, de-stoner, optical selector and indented cylinders,
working consecutively. All of this equipment utilizes differences in grain
shape, size, colour and density to ensure the efficiency of the cleaning
process.

The last step of the cleaning process is tempering. This is performed
through addition of measured quantities of water to the grain through a
spray nozzle (to ensure a uniform moisture distribution), a process that
raises the moisture content of the kernels to about 15 %. During the tem-
pering steps, moisture penetrates through at least a portion of the outer
bran layers, but does not entirely permeate the grain. Due to this moisture
pickup, the outer bran layers become softer and, thus, are more easily sepa-
rable from the starchy endosperm. Tempering periods for rye grains are
shorter than those for wheat because of the softer rye endosperm. The rye
milling process includes three to five breaks, up to two sizings and four to
six reduction passages. Reduction is achieved by corrugated rolls instead of

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236 Cereal grains for the food and beverage industries

smooth rolls (used for reducing wheat middling into flour). This is because
they would flake the middlings (due to the high pentosan content) (Bushuk,
2001b). Because of the sticky nature of rye flour, rye milling needs a sifting
surface 25–30 % larger than is required for wheat.

Rye flours are generally classified on the basis of ash content. In Germany,
up to seven different rye flours are produced with an ash content ranging
from 0.90 to 1.80 % (dry basis) (Deutsches Institut für Normung, 1991). In
both the USA and Canada, rye flour is also graded, although the number
of rye flours produced is smaller (up to 3).

6.3.2 Food uses for rye
Rye grain has different avenues of utilization. Generally it is milled into
flour for producing various forms of bread and other baked products that
represent the main food products in the major rye-consuming countries –
Poland, Germany, Scandinavian countries and Western Russia (Seibel and
Weipert, 2001b).

Many types of rye baked products exist. These include: ‘black bread’
containing high levels of rye flour (Meuser et al., 1994); crisp bread (Knaecke-
brot), often made with combined whole rye and wheat flour, with or without
yeast leavening and characterized by an excellent shelf-life; and pumper-
nickel bread originating from Westphalia, Germany and produced from
100 % rye meal using sourdough technology. It is characterized by an
extremely long fermentation (18–36 h), has a very long shelf-life and
includes rye–wheat bread, containing at least 50 % rye, wheat–rye bread
containing at least 50 % wheat and 10 % rye, wholemeal rye bread and rye
rolls. In addition to leavened breads, rye is also widely used for the produc-
tion of biscuits, crackers and different snack foods where rye is incorporated
in the form of cracked grain, as rye flakes or as extruded rye (Bushuk, 2004).
In North America and Canada, a wide range of rye breads are available:
American rye bread (light rye bread) with good grain and softer texture,
usually made with a high proportion of wheat flour (60–80 %); sourdough
rye bread with a heavy crumb structure made using various combinations
of wheat and rye flours (Decock and Cappelle, 2005; Michalska et al., 2008);
US pumpernickel bread made by the sourdough process with or without
molasses; and pan rye, a sweet rye bread made with 10–40 % of rye flour
and 60–90 % wheat flour and syrup using a straight-dough process (Bushuk,
2001b). Bakeries have developed new bread and buns that contain, in addi-
tion to whole-grain flour, crushed rye grain and groats. Moreover, the inclu-
sion of sourdough in the bread products allows a reduction in the amount
of salt added because sourdough acidity increases the perceived saltiness
intensity (Keast and Breslin, 2003).

In the Nordic countries, rye has been utilized in many other food prod-
ucts besides bread, such as breakfast cereals, muesli and porridge (kasha).
These products are generally made of whole-grain rye. In breakfast cereal,

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Rye 237

rye is generally flaked and precooked, and sometimes even extruded to
increase crispiness and taste (Kujala, 2008). Rye porridge is traditionally
made from rye flour, but nowadays rye flakes are also available for a good
and tasty porridge. Interestingly, rye novelties include pasta products which
contain rye to positively influence the colour and taste of the final products
(Kujala, 2008). Some experiments have also been performed with rye as a
raw material in the production of confectionary products and coffee sub-
stitutes (Pazola and Cieslak, 1979).

6.3.3 Alcoholic rye beverages

Rye beer
Rye beer (roggenbier) originated in Bavaria, in Southern Germany, and is
a speciality beer produced with up to 60 % rye malt. This is characterized
by high viscosity, due to the high content of pentosans and, as a result, is
extremely difficult to filter (Meussdoerffer and Zarnkow, 2009). The deep
colour of rye malts is carried on to the final product. Rye malt results in a
pleasing, unfiltered, dark, top-fermented speciality beer. Recently, roasted
rye speciality malts have become available, and their range of applications
is similar to those of roasted spelt and barley malts (Meussdoerffer and
Zarnkow, 2009).

Rye whiskies
Rye is an important cereal for the production of whiskey. Unlike
Canadian rye whiskey that can be made with different percentages of rye,
American rye whiskey must be made from a minimum of 51 % rye, distilled
at less than 80 % ABV (alcohol by volume), and aged for a minimum of
two years in new charred casks (Buglass et al., 2011). Rye whiskey has a
characteristically pungent aroma and hard-edged spicy, grain-like flavour.
Nowadays, the major brands of straight rye whiskey are produced by the
Bourbon distillers of Kentucky and Indiana, as well by Jack Daniel’s Dis-
tillery in Tennessee (Buglass et al., 2011).

6.4 Conclusions

Since the 1970s, rye has ranked last of the eight cereal grains (corn, rice,
wheat, barley, sorghum, millet and oats) grown for human consumption with
a reduction in its world production of around 50 %. However, more recently
its producer price has doubled, mainly due to an increased consumer aware-
ness of its health-related benefits. Rye is of special importance due to its
dietary fibre contribution as it is generally consumed as whole grain. It is
also useful for avoiding constipation, for managing glucose metabolism and
reducing cholesterol absorption.

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238 Cereal grains for the food and beverage industries

Additionally, preliminary studies on whole-grain rye have pointed
towards a link between rye components and cancer-protective effects. This
may further boost the human food rye market. However, additional medical
research must verify this possible relationship between minor rye constitu-
ents and health benefits.

6.5 Future trends

Rye can be successfully utilized as a major ingredient in new types of func-
tional foods, especially because they represent a rich source of fibre, vita-
mins, minerals and bioactive phytochemicals (Liu, 2007).

One of the main future goals for the rye grain is to improve its bread-
making quality using both conventional breeding processes and genetic
engineering (GE). This would allow development of genetically modified
breeds, through biotechnological transformation techniques to introduce
genes related to, for example, the strength-conferring glutenin polypeptides
of common wheat, thus improving rye baking qualities. Despite the poten-
tial of the GE approach (Vasil et al., 2001), a transgenic rye would have to
overcome perceived customer resistance to GMO material in the human
food supply (Wrigley and Bushuk, 2010).

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© Woodhead Publishing Limited, 2013

p
s

s

100.0 µm
Plate VI Confocal laser scanning microscope (CLSM) micrograph of portion of
starchy endosperm; s: starch; p: protein. The portion of the endosperm was stained
with fluorescein isothiocyanate (FITC) for starch (green) and with rhodamin B for

protein (red).

Starchy endosperm

50.0 µm

Vitreous endosperm

Plate VII Confocal Laser Scanning Microscope (CLSM) micrograph section of
the teff kernel with starch storage granules stained with fluorescein isothiocyanate

(FITC) for starch (green) and with rhodamin B for protein (red).

© Woodhead Publishing Limited, 2013

7

Oats

DOI: 10.1533/9780857098924.243

Abstract: Like all other cereal grains, oats belong to the Poaceae (also known as
the Gramineae) family; among the cultivated oats, Avena sativa is the most
important crop. Oats are the sixth most significant cereal crop in the world, with
production exceeding 24 million tonnes annually. Primarily, oats have been
utilized as feed for domestic animals, particularly horses and dairy cows. However,
recent advancements in food and nutrition have revealed the importance of their
various components. They are a good source of soluble fibre, essential amino
acids, unsaturated fatty acids (oleic, linoleic and linolenic acid), vitamins (B1),
minerals (phosphorous and iron) and phytochemicals (avenanthramides). The
health effects of oats have been primarily attributed to the highly viscous
β-glucan fraction, which has the ability to lower blood cholesterol and the
intestinal absorption of glucose. Although some antinutritive elements (enzyme
inhibitors and phytic acid) are present in oats, their effect on nutritive value is
nearly negligible. Food uses for oats include as oat bran, oat meal, oat flour and
oat flakes, which are mainly consumed as breakfast cereals. Other food products
processed from oats are infant foods, muesli, granola bars, breads and biscuits or
cookies. In brewing, oats are mainly used as an ingredient to improve the pleasant
flavour properties of the final product. Additionally, new processes have been
recently developed to manufacture non-dairy functional products using oats.

Key words: oats, chemical composition, oats utilization in food and beverages.

7.1 Introduction

Oats are an important source of livestock feed worldwide, both as forage
and as a nutritious grain, and have played a significant role in farming
systems from domestication to the present time due to the versatile uses of
the grain, and plant. Oats, like all other grain varieties, belong to the Poma-
ceae family. Avena sativa L. (common oat) is the most important variety
among those cultivated. The generally known oat species, diploid, tetraploid
and hexaploid oats, are shown in Table 7.1 (Youngs et al., 1982; Lásztity,
1998; Butt et al., 2008). Among the cereal grain crops, oats were considered
the primary protein source in feed rations until they were replaced by soy-
beans. They are also a good source of fibre, fat and minerals. Oats are more

© Woodhead Publishing Limited, 2013

Table 7.1 Taxonomic classification

Botanical classification Description

© Woodhead Publishing Limited, 2013 Kingdom Plantea: plants Most important cultivated oat, particularly adapted
Sub-kingdom Tracheobionta: vascular plants to temperate climates.
Superdivision Spermatophita: seed plants
Division Magnoliophita: flowering plants Cultivated oat, grown in warmer climates generally
Class Liliopsida: monicotyledons as a winter oat; often crossed with A. Sativa.
Subclass Commelinidae
Order Cyperales Wild, considered one of the worst cereal weeds in
Family Poaceae the world.
Genus Avena: oat
Species Wild, particularly in Mediterranean area.
A. sativa L. Hull-less or naked oats; limited commercial
Hexaploids (2n = 6x = 42)
A. byzantine C. Kock production.
Tetraploids (2n = 4x = 28) Mostly wild species growing in Northern Africa
A. fatua L.
Diploids (2n = 4x = 14) and Mediterranean area. A. barbata is also found
A. sterilis L. in California. Some are grazed.
A. nuda L. Mostly wild species growing in the Mediterranean
area. A. strigosa is cultivated in the Middle East.
A. abyssinica Hochst., A. vaviloviana Mord.,
A. barbata Pott ex Link, A. murphyi Ladizinsky,
A. magna Murphy et Terrell

A. canariensis Baum. Rajhathy et Sampson,
A. clauda Dur., A. pilosa M. Bieb.,
A. damascena Rajhathy et Baum,
A. hirtula Lag., A. wiestii Steud.,
A. longigiumis Dur., A. prostrata Ladizinsky,
A. strigosa Schreb., A. ventricosa Bal

Sources: Butt et al. (2008), Lásztity (1998), Youngs et al. (1982).

Oats 245

tolerant to cold and rain than other cereals with ~ 67 % of the world pro-
duction occurring in the northern hemisphere. Canada, the USA, Russian
Federation, China, Finland and Poland represent the top six countries for
world oat production (Belitz et al., 2004). Between 50 and 90 % of the world
oat production is used as animal feed for horses, cattle and sheep. However,
oats are also used in production of many human food products and have
some industrial applications. Food uses for oats include oat bran, oat meal,
oat flour and oat flakes which are mainly used for breakfast cereals. Por-
ridge, hot cereals, bread, biscuits, infant food, muesli and granola bars are
a few examples of food products produced from oats. The valuable physi-
ological and nutritional attributes of oat products (e.g. lowering blood cho-
lesterol, reducing risk of colorectal cancer by β-glucans and other dietary
fibre components, high tocopherol and natural antioxidant level) have gen-
erated an increased demand for oats in human nutrition (Zwer, 2004).These
beneficial effects provide opportunities for adding value to the oat crop.

7.1.1 History, production, price, yield and area
Oat is a cereal crop of Mediterranean (Iberian peninsula, North-western
Africa) and Middle East origin (Iran, Iraq and Turkey). The domestication
of oats occurred much later than for wheat and barley (Murphy and
Hoffman, 1992). In fact, when wheat and barley moved into the European
continent, Great Britain and East Asia, where oats and rye were present as
weed contaminants. However, oats still rank among the oldest crops culti-
vated by mankind. Grains of oats dating from 10 500 BC. were found in the
Franchti Cave in Greece (Hansen, 1978; Youngs et al., 1982). Some of the
earliest records of oats being grown as a grain crop date back to the period
of the Roman occupation of Europe. There are references to oats for
fodder, animal feed, human food and medical properties by Greek and
Roman authors ~23–79 AD (Zwer, 2004).

The Greeks were very familiar with oats and called the crop vromos or
bromos, whereas the Romans called it avena. The word avena to indicate
oats was apparently used by the Latin countries long before 1753, when
Linneaus designated avena as the generic name. As reported by Denaiffe
(1901):

The derivation of the Latin word Avena remains somewhat obscure. It seems
probable that it is from the Latin word Aveo (to desire), that is to say, forage
desired by all animals.

Writings in the eighteenth century describe oats as being primarily a feed
for horses and livestock in England and other parts of Europe. Although
the primary use of oats was for animal feed, by 1500–1700 they had become
an important part of the human diet in Scotland, Wales, Britain and Ireland.
In these latter countries, oats were used in soup to sustain the hungry during
the potato failure from 1740–1741. Oats were introduced to the USA and

© Woodhead Publishing Limited, 2013

246 Cereal grains for the food and beverage industries

southern Canada in 1500–1800 as an animal feed by immigrants and explor-
ers from Great Britain and Spain, and also to Australia and New Zealand,
where they became an important winter season crop.

Nowadays, oat production ranks sixth in world-production statistics, fol-
lowing corn, wheat, barley, sorghum and millet (Table 7.2). Oats represent ~
1 % of the total grain production. Worldwide, oat production has been in a
stable decline as the demand for oats for horses has decreased sharply and
farms have became mechanized. Nevertheless, in the last five years oat pro-
duction has stabilized at slightly more than 24 million tonnes (Table 7.2).
Canada, Russian Federation, the USA, the 27 states of Europe (EU) and
Australia represent ~ 77 % of the world’s supply of oat grain, seed and
industrial-grade oats. The yield in most regions ranges from 1.4 to 3.7 dry
tonnes/ha−1, and the global average yield is 2.24 dry tonnes/ha−1. The highest
yield occurs in Ireland with 7.1 dry tonnes/ha−1, over three times greater than
the global average yield. Land area destined for oat production has fallen
substantially over the past 40 years from 38 million hectares in 1961 to
slightly more than 9 million hectares in 2010 (FAO/UN, 2012) having being
displaced by higher value crops, such as soybean or other oilseed crops
particularly suitable for animal feed due to their higher protein content.

Oats usually provide the highest return per hectare when sold to food
consumption markets with reasonably good returns for growers. The pro-
ducer price evolution (from 2000–2009) of oats, expressed in US $/tonne, is
reported in Table 7.3. It is possible to observe high variability in terms of
the producer price depending on the production country. Generally, the oat
price doubled over the last 10 years, moving from 121 US $/tonne in 2000
to 199 US $/tonne in 2009 (Table 7.3). During the last 10 years, Cyprus and
Italy always showed, among the oat producer countries, the highest pro-
ducer price at 513 US $/tonne and 379 US $/tonne, respectively. In Canada,
the forward-contracting programme, developed in the early 1990s, resulted
in a sharp increase in the production of higher quality oats and a huge
annual increase in exports. Using this programme, Canadian commercial
milling companies contract forward for large tonnage from growers, up to
90 % of the high-quality oats they grow at a guaranteed price (Strychar,
2011).

7.1.2 Phytology, classification and cultivation
Oats are a cereal grain of the family Graminaceae (Poaxeae). They occur at
three ploidy levels, diploid, tetraploid and hexaploid, with a base chromo-
some number of 7 (Table 7.1). The genus Avena was apparently established
in the year 1700 by a French explorer and botanist Tournefort. Most species
of oats known today were described as early as 1750 by Linnaeus, the great
Swedish taxonomist. In 1953, Stanton conducted comprehensive studies
on the identification and classification of oats, describing 12 species or sub-
species of Avena. Among these are A. sativa, A. byzantina, A. fatua, A. nuda

© Woodhead Publishing Limited, 2013

Table 7.2 World cereal production in million tonnes and as a percentage of total cereal production

© Woodhead Publishing Limited, 2013 Grain Crop years Five-years Percent
2004 2005 2006 2010 averagea of total
2000 2001 2002 2003 2007 2008 2009

Maize 592.4 615.5 604.8 645.1 728.8 713.4 706.6 789.6 826.7 818.8 840.3 796.4 46.4
Wheat 585.7 589.8 574.7 560.1 632.7 626.8 602.9 612.6 683.0 685.6 653.6 647.54 37.7
Barley 133.1 143.9 136.7 142.5 153.8 138.6 139.5 134.11 154.7 152.2 123.5 140.802
Sorghum 55.7 59.6 59.6 57.4 62.0 65.8 56.1 55.7 59.4 8.2
Millet 27.6 28.9 53.3 58.8 57.8 30.9 31.8 33.7 34.9 26.7 31.6 31.74 3.5
Oats 26.1 27.33 23.9 34.8 29.6 23.7 22.7 25.8 25.8 23.2 19.6 23.42 1.8
Rye 20.1 23.4 25.4 26.5 26.0 15.1 12.6 15.1 18.1 18.2 12.4 15.28 1.4
Mixed grain 20.9 14.6 17.7 0.9
Total 4.3 5.2 4.9 4.9 4.4 5.2 4.5 4.8 4.3 4.64 0.3
1445 1493 1444 7.7 5.5 1613 1577 1678 1813 1785 1736.7 1717.94 100.0
1490 1651

a2006/2010.
Source: Data from FAO/UN (2012).

Table 7.3 Producer prices (US $/tonne) of oats from 2000–2009

Crop years

Countries 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009

© Woodhead Publishing Limited, 2013 Albania 208.8 209.1 214 246.2 340.5 340.4 357 303.2 405.3 358.4
Algeria 146.2 142.5 138 193.8 208.2 204.7 220 231 247.7 220.3
Argentina 103.1 121.1 116.2 172.4 250.8 349.2 375.5 463.7 540.3 180.6
Australia 61.5 68.3 95.1 142 101.6 102.4 110.7 202.1 235.7 171.4
Austria 108 197.4 159.7 100
Azerbaijan 87.9 89.7 84.7 99.3 95.7 87.2 132.9 139.7 144.8 172.8
Belarus 101 69.4 80 94.9 103.7 103.1 59.5 105.6
Belgium 73.2 56.2 50.4 46.5 55.5 57.8 111.5 68.9 198.3 77.8
Bolivia (Plurinational State of) 116.7 113.1 96 106.1 109.4 103.4 123.3 130.6 176.3 217.2
Bosnia and Herzegovina 141.2 135.3 125.9 120.4 119.7 120 175.5 131.1 416 183.7
Brazil 169.6 211.4 142.9 199.1 215.5 212.1 122.1 331.5 188.5 210.7
Bulgaria 83.1 83.1 99.6 115.5 109.6 111.4 103.3 146 202.7
Canada 73.5 83.3 71.3 103.9 118.2 102.4 112 137.4 184.6 180
Chile 59.3 82 117.2 102.1 93.9 95.8 154.3 151.5 255.5 128.5
China 120.5 99.4 122 127.9 113.6 133.1 188.1 233.7 367 199.1
Croatia 49 72.4 109.1 159.6 141.6 141.2 141.8 322.1 294.8 395.3
Cyprus 93 126.1 116.4 156.2 178.6 150.7 545.2 192.5 769.1 182.4
Czech Republic 401.7 388.7 343.9 405.8 448.7 506.9 145.7 594.5 250.4 730.6
Denmark 121.5 140.2 169.8 155.6 137.9 141.7 177.4 245.2 147
Ecuador 98.1 100.3 99.7 115.1 124.5 124.9 177.6 252.8 352 140.2
Estonia 114.3 146 140 160 242.7 205.1 129.8 209.6 95.2
Ethiopia 172.1 58.8 65.5 79.9 107.4 103.4 238 202.6 451.1 77.1
Finland 57.5 125.3 91 150 194.3 192.5 134.4 307.3 202.1 349.5
France 135.1 99.6 97.9 103.8 108.2 108.4 131.7 205.6 200.8 119.4
Georgia 109.1 108.7 80.7 94.2 98.8 105.8 126.1 232.9 215.9 118.1
Germany 96.5 187.2 179 199.9 235.8 260.9 119.3 187.9 218.3 100.8
Greece 207 92.3 87.5 101.6 120.6 102.2 217.5 217.9 346.4 127.8
Hungary 98.3 176.1 155 196.7 224.5 234.7 104.9 309.4 196.7 304.2
Ireland 171.7 85.4 82.9 113.6 116.3 91.1 160.7 224.6 191.9 134.3
88.4 87.5 91.3 120.8 124.3 132.1 259.1 156.9
97.1

© Woodhead Publishing Limited, 2013 Italy 333.6 325.8 322.1 371.8 379 282.7 422.4 432.6 665.3 255
Kazakhstan 35.2 38.5 43.8 38.7 51.4 58.9 65.4 71.2 100 91.8
Kyrgyzstan 53.8 70.3 78.5 72.8 74.1 79.9 92.8 136.4 117.3 171.4
Latvia 85.7 78 84.1 91 100 90.5 105.4 193 143.5 98
Lithuania 60.3 71.3 81.6 102.6 99.7 83.8 108.4 204 169.7 82.2
Luxembourg 93.6 81 70.4 85.2 93.2 93.4 109.9 191.9 146.5 92.6
Mexico 212.1 181.7 194.4 170.4 195.7 199.3 191.2 187.5 189.6 237.3
Mongolia 68.9 59.8 67.1 69.9 75.6 82.1 86.5 93.1 214.5 229.8
Morocco 274.8 236.2 191.5 201.6 203.1 250.7 258.2 355.6 476.1 353.2
Netherlands 106.2 100.7 95.1 125.3 126.8 128.3 158.2 263.2 222.7
New Zealand 87.2 84.1 115.6 174.2 192.6 204.3 188.4 236.3 272 334.8
Norway 184.1 178.8 207 228.5 226.5 234.8 244.9 277.6 322.7 313.9
Peru 217.8 233.8 213.3 209.9 269.7 218.5 235.3 243.1 338.5 355.5
Poland 89.5 91.6 79.4 103.9 103.3 90.4 112.6 191.4 208.8 99.4
Portugal 94.5 117 103.5 198.6 186.5 223.9 128.5 212.7 243.3 197.5
Republic of Moldova 113.1 92.3 66.6 119.8 125.4 103.3 110.8 189.8 242.8
Romania 84.9 78.5 62.7 100.6 91.7 161.3 160.4 312.2 404.9 230.3
Russian Federation 58.2 58.4 48.1 54.3 84.8 88 92.6 116.8 152.8 125.1
Serbia and Montenegro 75.8 113.9 119.5 137.4 138.1 130.6 0 0 155
Slovakia 89.5 100.1 102.2 127.1 158.6 144.4 147 205.6 0 243.6
Slovenia 128.2 138.4 147.4 182.4 153.1 151.1 160.4 241.4 233.4 243.8
South Africa 104.8 98.4 90.1 145.4 163 145.8 145.6 232.4 324.9 160
Spain 109.1 111.6 118.6 138.8 155.4 176.9 160.7 216.8 248.8 176.3
Sweden 96 96.5 96.3 95 103.6 110.8 138.1 217.9 250.6 101.2
Switzerland 248.7 234.1 253.4 286.6 282.6 279.2 272.2 276.9 173 261.1
Tajikistan 144.5 132.8 108.5 101.3 117.9 119.8 106.8 116.3 283.4 111.7
The former Yugoslav Republic of Macedonia 106.7 105.5 178.3 196.4 171.3 233.5 148.6 267.6 131.2 214.1
Turkey 133.9 104.8 131.2 184.5 217.2 238.2 217.7 285 194.7 290.3
Ukraine 63.6 60.9 50.1 74.4 68.8 65.2 83 147.7 380.2 81
UK 101.4 97.9 89.9 94.7 113.6 122 140 216.2 160 128.1
USA 76 110 125 102 102 112 129 168 189.4 139
Uruguay 155 96.6 121 145.3 169.2 139.3 196.2 186.1 227 320.8
World average price 121.66 119.99 119.5 143.07 154.94 156.78 162.05 220.5 224.9 199.61
254.27

Source: Data from FAO/UN (2012).

250 Cereal grains for the food and beverage industries

and A. abyssinica. There are annual and perennial oats, but all cultivated
varieties are annuals and these will be the focus of this chapter.

Most of the cultivated oats belong to the hexaploid group. A. sativa L.
(common white oat) is the most important, and grows mainly in the temper-
ate zones of the world. A. sativa spread from the East to Central-North
Europe in the late Bronze Age while A. byzantina Kock (red oat) was the
main form of cultivated oats in North Africa and Spain. Both Aveana types
were introduced to North America in the sixteenth century (Coffman,
1977). However, sativa types were more suited to spring sowing at high lati-
tudes, while byzantine types formed the basis of the autumn-sown crop, to
escape the hotter, drier summers of the Southern USA. During the twenti-
eth century, both types of oats were interbred, so that current cultivated
oats in the USA are the result of crosses between A. byzantine and A. sativa
(Lásztity, 1998). A. nuda (naked oat) is the ‘black sheep’ of the cultivated
oat family because it is always short on performance (lower yield, unpro-
tected grain is prone to mechanical damage caused by combine harvesting
and attacked by moulds) (Stanton, 1923; Valentine, 1995). However, it has
high nutritional quality (higher in essential amino acids than wheat or
barley) and is thus attractive to producers and industries, particularly spe-
ciality markets (Peltonen-Sainio et al., 2001).

Oats are considered to be a crop that adapts well to a wide variety of
soil conditions such as acidic (4.5) and alkaline soils (8.5), although the best
yield performance occurs with pH range from 5 to 6. Oats are also com-
monly resistant to high manganese levels in the soil (Zwer, 2004). Culti-
vated oats are an annual crop with tall and short stature depending on the
presence of dwarfing alleles. The fibrous root system consists of two groups,
the seedling roots and the permanent roots, both varying according to
above-ground growth as well as maturity, but is ~1 m deep (Bonnett, 1961;
Zwer, 2004). Each plant produces ~ five culms, or stems, depending on the
growing season. Each oat stem is composed of a series of nodes and inter-
nodes, with alternate sessile leaves. At the mature stage, stems may termi-
nate in a loose open panicle where the seeds develop. The panicle consists
of the main axis terminating in a single or multi-florous spikelet.

7.1.3 Structure of the oat kernel
The oat fruit is a caryopsis (Fig. 7.1) furrowed on the side opposite to the
embryo. Figure 7.2 shows the anatomy of a caryopsis (enclosed within the
hull). The caryopsis (or groat) is tightly covered by a hull or husk which
developed from the lemma and palea. The hull represents about 30–40 %
of the total grain weight and mainly comprises cellulose and hemicellulose
(Welch, 1995) with a lesser amount of lignin or related phenolic compounds.
Inside the protective hull, the caryopsis shows similar appearance to the
other common cereals such as wheat and barley, although the oat caryopsis
is generally longer and more slender (Fig. 7.1) than that of wheat or barley

© Woodhead Publishing Limited, 2013

Oats 251

Fig. 7.1 Oat grains.

kernels. It is, however, covered with numerous trichomes (or hair-like pro-
tuberances) located mostly at the distal end of the kernel (Figs. 7.2 and 7.3).

The caryopsis is composed of three main parts – bran, endosperm and
germ (Fig. 7.2). The germ accounts for 3 % of the caryopsis weight, the bran
is 38–40 % and the starchy endosperm is 58–60 % (Lásztity, 1998). Differ-
ences are due to both variety and environment. Starting from the outside
of the caryopsis, the bran layers of the caryopsis, and in particular the aleu-
rone layer, are particularly rich in vitamins, minerals, phytate and anti-
oxidant compounds (Peterson et al., 1975; Marlett, 1993; Kent and Evers,
1994). The bran layers consist of the pericarp, the seed coat, the nucelus, the
aleurone layer and a larger portion of subaleurone starchy endosperm than
is found in wheat bran (see Plate Va in the colour section between pages
230 and 231). Chemically, oat bran contains 67.9 % carbohydrates, 15–22 %
dietary fibre protein, 10.4 % β-glucan, 8.6 % fat, 1.3 mg/100 g niacin, 171 mg/
100 g magnesium, 6.4 mg/100 g iron, 0.17 mg/100 g copper, 441 mg/100 g
potassium and less than 0.5 mg/100 g of α-tocopherol (Marlett, 1993).

The starchy endosperm is the most predominant organelle of the mature
oat kernel, as in all of the cereal grains, and may represent between 55 and
70 % of its weight (Youngs, 1972). The endosperm is the primary storage
site of protein, starch, lipid and β-glucan enclosed by only one cell type.
β-glucans are mainly located in the endosperm cell wall.They are unbranched
polysaccharides of β-D-glucopyranosyl units with 70 % 1–4 linked and 30 %

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252 Cereal grains for the food and beverage industries

Trichomes (hairs) A
Hull
B
Endosperm C
Aleurone cells
Bran
Scutellum
Plumule

Radicle

Fig. 7.2 Longitudinal section through an oat kernel.

1–3 linked (Butt et al., 2008). Most of the proteins, lipids and β-glucans are
found in the periphery regions of the starchy endosperm, whereas, in the
grain’s inner regions, the starch concentration dominates (Miller and
Fulcher,2011).The endosperm protein bodies of oats ranges from 0.3–5.0 µm
in diameter and are round, angular to irregular in shape (Bechtel and
Pomeranz, 1981) differing from both the concentric-ringed protein bodies
found in rice, maize, sorghum and millets and the matrix type of storage
protein typically found in barley, wheat, rye and triticale. In the starchy
endosperm, two types of starch granules can be detected – simple starch
granules and compound granules composed of several granula (Plate Vb).

The oat germ or, botanically speaking, the embryo represents approxi-
mately 3 % of total kernel weight. It is formed by the embryonic axis and
the scutellum and represents a viable structure capable of metabolic activity

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Oats 253

200.0 μm
Fig. 7.3 Oat hairs (or trichomes).

Table 7.4 Chemical composition of oat and other cereals (average values)

Nutrients (g/100 g) Oat Wheat Rye Corn Barley Rice Millet

Water 8.22 9.27 10.95 10.26 9.44 10.37 8.67
Carbohydrate (total) 66.27 75.90 69.76 76.89 73.48 77.27 72.85
Protein (N × 5.83) 16.89 11.31 14.76 8.12 12.48 7.94 11.02
Total lipid (fat) 6.90 1.71 2.50 3.59 2.30 2.92 4.22
Fibre 9.7 13.3 13.2 9.7 9.8 2.2 3.8
Ash 1.72 1.52 2.02 1.13 2.29 1.53 3.25

Source: Compiled from data in USDA (1989).

(Plate Vc) (Miller and Fulcher, 2011). From a chemical point of view, oat
germ contains high levels of proteins and lipids but very little starch. The
protein bodies of the germ (scutellar parenchyma) contain phytin globoids
that sequester much of the phosphorous content of the caryopsis as well as
iron, magnesium, manganese, potassium and calcium albeit in smaller
amounts (Buttrose, 1978).

7.2 Oat carbohydrate composition and properties

The rising attention given to the use of oats and oat constituents for food
production, together with the beneficial effects of some oat compounds in
nutrition, has resulted in an increased interest in the study of the chemical

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254 Cereal grains for the food and beverage industries

Table 7.5 Chemical composition of oat grain, groat and flour

Sample Protein Carbohydrate Lipid Fibre Ash

Whole oat 7.7–14.8 53.0–65.8 4.3–7.6 6.5–12.8 2.3–4.2
Oat groats 21.2 39.3 15.5 5.7 –
Oat grain
Oat flour 8.7–16 39.0–55.0 4.5–7.2 20.0–38.0 2.1–3.6
Oat bran 15.5 – 6.2 3.6 2.1
18.1 9.6 15.4 3.1
44.6

Source: Adapted from:Lásztity, R., Oat grain – a wonderful reservoir of natural nutrients and
biologically active substances. Food Reviews International, 1998. 14(1): p. 99–119, reprinted by
permission of the publisher (Taylor & Francis Ltd, http://www.tandf.co.uk/journals).

composition of oats. As a result of research efforts, knowledge of oat con-
stituents, mainly biologically active minor components, has rapidly increased.
The proximate chemical composition of oats is characterized by high
carbohydrate/primary starch content, considerable protein, non-starch/
dietary fibre and vitamin and mineral contents (Table 7.4) (US Department
of Agriculture, 1989). The major kernel constituent is carbohydrate, mainly
represented by starch, with minor amount of oligosaccharides and sugars
that together account for less than 1 % of oat meal. Protein contents in oats
are similar to those detected in wheat and generally higher than in corn,
rice or barley, which are instead carbohydrate-rich. Oats contain much
higher levels of lipids than any other cereal grain (Aman and Hesselman,
1984; Kent and Evers, 1994) (over two-fold) distributed throughout the
endosperm, unlike other cereals where fat is mainly localized in the germ
(Evers and Millar, 2002). Oat fibre is the most variable constituent, with
more than a five-fold variation across species. The mineral content of oats
is generally 2–3 %. As in other cereals, phosphorus, potassium, calcium and
magnesium are the major minerals (Lásztity, 1998).

The distribution of each constituent between botanical parts of the oat
kernel is irregular. Consequently, considerable differences may be observed
between gross chemical composition of total grain, groat and different oat
products (Table 7.5).

7.2.1 Starch
Oat starch, mainly stored in the oat endosperm (Fig. 7.2b), is the most
abundant carbohydrate component of oats and its content varies between
40 and 50 % (Sayer and White, 2011), depending on the variety and growing
conditions. Unlike the starch morphology observed in cereal grains (dis-
crete granules which are solid, optically clear bodies), oat starch granules
are only slightly birefringent, irregularly shaped (often polyhedral but
sometimes ovoid or hemispherical), and tend to exist in clusters not falling
into discrete size distributions like in wheat and barley.

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The oat starch granules surfaces appear smooth without evident fissures
(Hoover and Vasanthan, 1992). The average size of individual oat starch
granules varies from 3 to 10 µm (Hoover and Vasanthan, 1992; Sowa and
White, 1992) (with most granules having a diameter range of 1.9–2.4 µm)
(Makela and Laakso, 1984), which is much smaller than starch granules of
wheat, rye, barley and corn (Hoseney et al., 1971).

Oat starch constituents can be divided into non-carbohydrate and car-
bohydrate components. The minor non-carbohydrate constituents of oat
starch are lipids, proteins and minerals (in particular phosphorous) which
influence the physico-chemical features of starch granules. Unlike corn,
wheat and rice starches, oat starch shows a higher lipid content, presumably
present as an amylose–lipid complex (Sowa and White, 1992; Zhou et al.,
1998a). Gudmundsson and Eliasson (1989) investigated the rheological and
thermal properties of starches isolated from different oat varieties. The lipid
content ranged between 5.0 and 7.5 %. The oat variety with the highest oil
content was closest to wheat starch in its rheological properties and retro-
graded least of all the starches which were investigated. However, a retro-
gradation study on defatted oat varieties did not show a clear relation
between oat oil content and the retrogradation tendency.

Lipids in oat starch seem also play a role in the mechanism of regulation
of starch biosynthesis, which partially explains the positive correlation
between lipid and amylose contents in cereal starch (Morrison, 1988).
However, high lipid contents in cereal starches exert unfavourable effects,
such as: (i) a reduction of water-binding capacity, swelling and solubiliza-
tion of starch (Swinkels, 1985); and (ii) formation of undesirable flavours
due to lipid oxidation. For this reason a roasting stage should be incorpo-
rated into the treatment of oats, to inactivate enzymes and thus prevent
rancidity.

Oat starch also contains a considerable amount of protein (0.3–1 %)
(Sowa and White, 1992; Gibinski et al., 1993; Shamekh et al., 1994, 1999;
Zhou et al., 1998a; Hoover et al., 2003) compared to wheat starch (0.04–
0.6 %), (Swinkels, 1985; Lineback and Rasper, 1988), corn starch (0.2–0.4 %)
(Swinkels, 1985; Galliard and Bowler, 1987), rice starch (0.01–0.1 %) (Cham-
pagne et al., 2004), barley starch (0.11 %) (Song and Jane, 2000) and rye
starch (0.09–0.40 %) (Verwimp et al., 2004). Despite the fact that a level of
up to 5 % protein doesn’t appear to have a significant influence on the
thermal properties of starch (White et al., 1989), adverse effects such as
colour formation in hydrolysates, foam building and development of mealy
flavours can be observed in high protein content cereal starches (Swinkels,
1985). The phosphorous content of oat starch is also higher (0.15–0.19 %)
in comparison to wheat, corn and waxy corn starches (Gibinski et al., 1993),
and probably is present in the form of phospholipids embedded in the
starch (Sowa and White, 1992).

Among the carbohydrate constituents, amylose and amylopectin repre-
sent approximately 98–99 % of the oat starch (dry weight) (Tester et al.,

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256 Cereal grains for the food and beverage industries

2004). In general, amylose is defined as a molecule with a comparatively
low degree of polymerization (DP) (3000) and a branching frequency with
a low α-1, 6 linkage frequency (< 1 %), while amylopectin tends to have
high DP (> 5000) and higher α-1, 6 linkage frequency (3–4 %) (Bruce and
Matthew, 2009). Amylose in oat starch ranged from 18 % (Paton, 1979) to
26–29 % (Morrison et al., 1984; Gudmundsson and Eliasson, 1989). However,
amylose contents of 30–34 % were measured by Sowa and White (1992),
using the iodine affinity method.

In summary, the main influences on starch properties come from the
relative proportions of amylose and amylopectin in starch granules, together
with the chain length distribution (Hoover and Vasanthan, 1994) and the
frequency and spacing of branch points within the amylopectin molecule
(Tester and Morrison, 1990).

7.2.2 Dietary fibre
The oat grain contains high amounts of non-starchy polysaccharides which
are the main constituents of dietary fibre. This can then be subdivided into
water-soluble and water-insoluble fractions. Water-soluble fibre in cereals
is composed of non-starchy polysaccharides such as gum, mucilage, pectin,
some hemicellulose, β-glucan and arabinoxylan. Insoluble fibre mainly con-
tains lignin (lipophilic phenolic polymer which can absorb bile acid) and
other non-starchy polysaccharides (cellulose and the rest of the hemicel-
luloses). The oat caryopsis contains 10.2–12.1 % fibre, of which 4.1–4.9 % is
soluble fibre and 6.0–7.1 % is insoluble fibre, depending on the oat genotype
(Manthey et al., 1999). Water-soluble dietary fibre can form viscous solu-
tions, thus (i) reducing the intestinal transit at the intestine level, (ii) delay-
ing the gastric emptying (Anderson and Bridges, 1988) and (iii) slowing the
glucose and sterol absorption by the intestine (Kahlon and Chow, 1997;
Wood et al., 1990), thus lowering the serum cholesterol, postprandial blood
glucose and insulin levels. Insoluble dietary fibres usually have a high water-
holding capacity which contributes to increased faecal bulk (Manthey et al.,
1999). From a safety standpoint, oat fibre has been well-tolerated according
to numerous clinical trials (Kahn et al., 1990). The most common unfavour-
able events detailed have been typical gastrointestinal (GI) symptoms (e.g.
flatulence) related to a high-fibre diet in general (Tapola and Sarkinnen,
2009). Moreover, the potential obstruction of the GI tract, due to a highly
efficient water-holding capacity, similar to that reported for guar gum
(Lewis, 1992), cannot be ruled out.

7.2.3 β-glucan
Oat β-glucan is a linear, unbranched polysaccharide that consists of
1–4-O-linked (70 %) and 1–3-O-linked (30 %) β-D-glucopyranosyl units
(Fig. 7.4). The main compositions of β-glucan molecules are β-(1–3)-linked

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Oats 257

CH2OH CH2OH CH2OH CH2OH CH2OH

O OO O O

O O

O OH O OH O

O OH

OH OH

OH OH OH OH OH

Fig. 7.4 β-glucan. With kind permission from Springer Science + Business Media:
European Journal of Nutrition, Oat: unique among the cereals, 47, 2008, 68–79. Butt,

M., Tahir-Nadeem, M., Khan, M., Shabir, R. and Butt, M.

cellotriosyl and cellotetraosyl units constituting about 90 % of polysac-
charides of β-glucan (Wood, 1991). This specific chemical structure is
responsible for physical properties, such as solubility, viscosity and potential
influence on cholesterol metabolism in the human body (Berg et al., 2003).

In cultivars with a high β-glucan content, β-glucan is mainly concentrated
in the starchy endosperm and, contrastingly, it is mainly localized in the
subaleurone region of those cultivars characterized by a low β-glucan
content. The β-glucan content in oats ranges from 2 to 8 g/100 g of oat
groats (Welch, 1995) and is seemingly influenced by genetic and environ-
mental factors. In comparison to the other cereals, oat β-glucan is present
in higher levels and is more readily soluble at 88 % which is much higher
that barley (69 %), cornmeal (67 %), whole-grain wheat (40 %) and whole-
grain rye (40 %) (Englyst et al., 1989).

β-glucan forms highly viscous solutions at low concentrations (> 0.3 %)
(Doublier and Wood, 1995) and it is not sensitive to pH or ionic strength
(Autio et al., 1992; Wood et al., 1994). The viscosity increases with concentra-
tion and molecular weight of β-glucan and has a negative correlation with
increasing temperatures (Dawkins and Nnanna, 1995).

Oat β-glucan has outstanding functional properties and is of immense
importance in human nutrition. It influences appetite through its chemical
and physical properties (particularly by bulking action), and increases vis-
cosity in the GI tract. Considering this latter property, several studies have
shown that oat β-glucan may reduce total blood and low-density lipoprotein
(LDL) cholesterol levels by forming a viscous layer in the small intestine,
inhibiting intestinal uptake of dietary cholesterol and reabsorption of bile
acids. This inhibition increases synthesis of bile acids from cholesterol and
reduces circulating LDL cholesterol levels (Table 7.6) (Anderson and
Bridges, 1993; Zhang et al., 1992; Lia and Andersson, 1994; Othman et al.,
2011). Moreover, numerous studies reported a significant inverse relation-
ship between the amounts of β-glucan viscosity of the products and post-
prandial glucose and insulin response (Wood et al., 1994; Tappy et al., 1996;
Wursch and PiSunyer, 1997; Jenkins et al., 2002; Granfeldt et al., 2007;Tapola

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258 Cereal grains for the food and beverage industries

Table 7.6 Suggested mechanisms for the cholesterol and glycaemic-lowering
impact of oat β-glucan

Beneficial effect Suggested mechanisms References

Lowering of (i) ↑ Viscosity in the Zhang et al., 1992
serum gastrointestinal tract Othman et al., 2011
cholesterol Anderson and Bridges,
levels ↓ Intestinal uptake of dietary
cholesterol 1993
Lowering
postprandial ↑ Bile acid excretion Wursch and PiSunyer,
glycemic ↑ Transportation of LDL 1997
response
cholesterol from the blood Tapola and Sarkinnen,
into hepatocytes 2009
↑ Plasma LDL cholesterol
removal Jenkins et al., 2002
↓ In lipoprotein cholesterol Battilana et al., 2001
secretion. Lia and Andersson,
(ii) ↑ Production of short-chain
fatty acids, which are 1994
fermentation products of Granfeldt et al., 2007
soluble fibre Venter et al., 1990
(-) Endogenous cholesterol
synthesis
(i) ↑ Viscosity of the meal bolus of
the stomach and small
intestine where the
absorption of nutrients occurs
↓ Absorption of the nutrients
from the small intestine
↓ Delayed carbohydrate
digestion and absorption
(ii) ↑ Rate of gastric emptying
(iii) ↑ Production of short-chain
fatty acids, including
propionic acid which has
been implemented as
inhibitor of the amylase
activity
↓ rate of starch digestion
↓ postprandial glucose response

Note: (-)-inhibition; ↑-increase; ↓-decrease, LDL-low-density lipoprotein.

and Sarkinnen, 2009). The postulated mechanisms for lowering postpran-
dial glycaemia with β-glucans are mainly related to (i) an increased luminal
viscosity leading to a prolongation of carbohydrate digestion and absorp-
tion (Battilana et al., 2001), and (ii) an improvement of the fermentative
activity in the colon resulting in the colonic production of short-chain fatty
acid (SCFA), including propionic acid, which has been implemented as a
moderator of hepatic glucose metabolism (Venter et al., 1990, Granfeldt
et al., 2007) (Table 7.5).

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In 1997, after reviewing 33 clinical studies, the United States Food and
Drug Administration (FDA) recognized the relationship between increased
soluble fibre intake and a decrease in serum total cholesterol concentra-
tions, allowing a health claim for oat soluble fibre (US FDA, 1997). The
required dose of β-glucan for a single food is 0.75 g/serving. Likewise, in
2004, the Joint Health Claims Initiative (JHCI) in the UK acknowledged
the importance of including oat β-glucan in the diets of people of all ages
to help reduce blood cholesterol levels and thereby the risk of coronary
heart disease (CHD) (JHCI, 2004).

7.3 Other constituents of the oat kernel

After carbohydrates, which are almost all present as starch, protein and fat,
particularly high in unsaturated fatty acid, are the most abundant constitu-
ents of the oat kernel.

7.3.1 Protein
Oat protein accounts for approximately 15–20 %, by weight (Table 7.4), of
the kernel depending on growing conditions and genotype (Peterson, 1992).
However, protein contents up to 24 % have also been reported (Webster
and Wood, 2011). While the distribution of total protein among the botani-
cal parts of the caryopsis is similar to that of other cereal grains, the protein
content of the groats is the highest among all cereals. The embryo contains
the highest protein content (over 30 %), followed by bran (20 %), starchy
endosperm (~10 %) and the hulls (> 2 %) (Youngs, 1972).

Globulin is the major oat storage protein in oats (characterized by a
better amino acid composition from a nutritional point of view due to the
high lysine content) while prolamin, the predominant storage protein of
most of other cereals, is present at a low level. In particular, wheat, rye and
barley prolamins constitute 40–50, 30–50 and 35–45 % of total proteins,
respectively. However, in the case of oats, prolamins represent only 10–15 %
of the total proteins (Brohult and Sandegren, 1954).

The quality (amino acid composition) of oat protein was seemingly unaf-
fected by nitrogen, phosphorous and potassium fertilization (Eppendorfer,
1978; Youngs et al., 1982), although the effect of deficiencies of these nutri-
ents on the yield was significant (Eppendorfer, 1978). Typical values for the
amino acid composition of oat caryopsis are shown in Table 7.7. From a
nutritional point of view, amino acids are classified into essential amino
acids (not synthesized by the human body or not in adequate amounts) and
non-essential amino acids. The nutritional quality of dietary protein is
related to the concentration of these essential amino acids in the protein,
compared with their nutritional requirements in the human body. The most
comprehensive report on amino acid composition of oat groat is that of

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260 Cereal grains for the food and beverage industries

Table 7.7 Amino acid composition of oat groat and wheat, and the recommended
levels of essential amino acids for adult humans

Amino acid Oat groata Wheat grainb FAO/WHO IUNV adult
(g /100 g protein) recommendationc

Essential 2.2 1.2 1.5
Histidine 3.9 4.2 3.0
Isoleucine 7.4 7.6 5.9
Leucine 4.2 2.9 4.5
Lysine 2.5 1.9 1.6
Methionine 1.6 2.3 0.6
Cysteine 5.3 5.3 1.9
Phenylalanine 3.1 3.3 –
Tyrosine 3.3 2.7 2.3
Threonine – 1.1 0.6
Tryptophan 5.3 4.5 3.9
Valine
5.0 3.8 –
Non-essential 6.9 4.8 –
Alanine 8.9 5.4 –
Arginine 23.9 32.5 –
Aspartic acid 4.9 4.4 –
Glutamic acid 4.7 10.8 –
Glycine 4.2 3.5 –
Proline
Serine

aAdapted from Pomeranz et al. (1971).
bAdapted from Jensen and Martens (1983).
cFAO/WHO/UNU (2007).

Pomeranz et al. (1971), which surveyed 289 samples representing the culti-
vars grown commercially in the USA and Canada between 1900 and 1970.
The authors reported that the chemical analysis of the oat hydrolysate
indicated that the oat groat proteins have an excellent amino acid balance,
nutritionally superior to the other cereal grains (Pomeranz et al., 1973;
Jensen and Martens, 1983). The lysine content of oats is higher than that of
– wheat proteins but still below the recommended FAO reference standard
of 4.5 % (FAO/WHO/UNU, 2007) while the glutamic acid (glutamine) and
proline contents are relatively lower (Table 7.6).

The negative relationship of lysine to overall protein content is typical
of cereal grain. However, unlike in corn and sorghum, where a 20 % and
27 % decrease in lysine corresponds to a 33 % and 33.1 % increase in
protein content, respectively (Sauberlich et al., 1953; Waggle et al., 1966),
the lysine content of oats decreased by only 5.8 % as protein content
increased 18.5 % (Hischke et al., 1968). These different amino acid composi-
tions (and protein quality changes) reflect, to some extent, the proportion

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Oats 261

of the various classic Osbourne protein solubility fractions. In most cereals,
increasing the protein content results in a relative increase in the prolamin
(generally low in lysine content) fraction and, as a result, overall protein
quality declines. In contrast, the increases of the protein content in oats are
primarily related to increases in the globuline fraction; thus, the protein
quality of oat protein is maintained more effectively at higher grain protein
levels than in other cereals.

Storage proteins
Seed proteins are generally classified into four types based on solubility:
albumin, globulin, prolamin and glutelin. Studies conducted by Robert
et al. (1983, 1985) indicate that the oat storage proteins mainly consist of
globulins and prolamins. The glutenin class of storage protein in oats, if
present, is a minor component. Generally the globulin fraction may account
for about 75 % of the total seed protein (Robert et al., 1983; Colyer and
Luthe, 1984). Extensive oat globulin characterization was performed by
Burgess et al. (1983) who identify and separate the globulins into three main
fractions with sedimentation coefficients of about 3S, 7S and 12S, of which
the last was the major component. They also observe that the oat storage
globulins have certain similarities to those present in legume seeds and
other dicotyledonous plants. In particular, the 12S globulin, an oligomeric
protein with a quaternary structure, of oats has the same native and poly-
peptide structure as 11S legume storage proteins (legumins) and the same
acid and basic nature of the polypeptide sub-unit groups (Brinegar and
Peterson, 1982).

Oat and coeliac disease
Coeliac disease (CD) is the most common food-induced enteropathy in
humans caused by intolerance to wheat gluten and similar proteins originat-
ing from barley and rye in genetically susceptible individuals (Arendt et al.,
2011). Gliadins, also called prolamins due to their high content of the amino
acids proline and glutamine, are described as the main triggering factor in
CD (Ciccocioppo et al., 2005). Oats do not contain gliadin but its counter-
part avenin (Dor and Shanahan, 2002). To the present day, medical nutrition
therapy (MNT) with supportive nutritional care (particularly in relation to
iron, calcium and vitamin deficiencies) is the only accepted treatment for
CD (Arendt et al., 2011). This means the dietary exclusion of wheat, rye,
barley and, until 1996, oats.

Several later studies (Srinivasan et al., 1996; Janatuinen et al., 2002;
Kemppainen et al., 2007; Guttormsen et al., 2008) indicate that oats are not
unsafe for those with CD, and thus oats are now often included in the CD
diet (Butt et al., 2008; Guttormsen et al., 2008). However, it is important to
keep in mind that, although most patients with CD seem to be able to toler-
ate oats, a considerable number of cases of intolerance to pure oats have

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262 Cereal grains for the food and beverage industries

been identified (Lundin et al., 2003; Arentz-Hansen et al., 2004; Silano et al.,
2007). Haboubi et al. (2006) suggest that oats should be excluded when
prescribing a gluten-free diet (GFD), and can be included only if the patient
is undergoing a lifelong regular review under specialist care. They also
highlighted that long-term risks of the inclusion of oats in the GFD remain
unknown.

7.3.2 Lipids
Lipids in food represent a concentrated energy source, and oats contain
(Lásztity, 1998) much higher levels of lipid than any other cereal grains
(Aman and Hesselman, 1984), which makes them an excellent source of
energy and unsaturated fatty acids (Brown et al., 1966; Saastamoinen et al.,
1989). According to reported data (Youngs, 1976–1978; Youngs et al., 1977;
Sahasrabudhe, 1979; Zhou et al., 1999), the lipid content in the oat grain
ranges from 3.1 to 11.8 %. Part of the variation in oil contents reported in
the literature is mainly due to the fact that some of the data reported refer
to the wholemeal oats while some refer to the dehulled oat kernels. Addi-
tionally, the method used for total lipid determination (solvent extraction,
nuclear magnetic determination, spectrometric determination based on
measurement in the near infrared region) (Brown and Craddock, 1972;
Williams and Sobering, 1993; Welch and Leggett, 1997) can significantly
influence the determination accuracy of the total lipid content (Zhou et al.,
1999). The kernel of some high-oil oat varieties may be high as 18.1 % (Frey
and Holland, 1999). However, in these cases the high lipid content of oats
was negatively correlated with their grain quality and agronomic perfor-
mance (straw yield, biomass, harvest index, heading date and height)
(Holland et al., 2001).

As in other cereal grains, the embryo fractions in oats (embryonic axis
and scutellum) are richest in lipids while the hulls had the lowest concen-
tration (Table 7.8). Most of the oat kernel lipids are located in the starchy
endosperm and bran because these caryopsis fractions alone represent the
greatest part of the total kernel weight (Youngs, 1972) (Table 7.6). The
total oat lipid can usually be fractionated into triglycerides, phospholipids,
glycolipids, free fatty acids (FFA) and sterols. Among them, triglycerides
represent the main lipid component (32–85 %). Phospholipids ranged from
5 to 26 % of the total lipid and lecithin (phosphatidylcholine) accounts for
45–50 % of the total phospholipid followed by phosphatidic acid (18 %),
phosphatidylinositol (10 %) and phosphatidylethanolamine (9 %). Glyco-
lipids account for 7–12 % of the total lipid, and the major glycolipid
components are galactolipids (Youngs et al., 1977; Sahasrabudhe, 1979).
There is a wide variation in the reported values for oat sterol contents
resulting in the range between 0.1 and 4 % (Youngs et al., 1977; Sahas-
rabudhe, 1979). The major sterol is β-sitosterol that accounts for ~ 40 %
of the total, followed by Δ5-avenasterol (21.2 %), Δ7-avenosterol (13.5 %),

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Table 7.8 Lipid concentration and distribution in the oat kernel

Fraction Lipid concentration Distribution in
(g/100 g, dry weight basis) the kernel (%)
Hull
Kernel Free lipid Bound lipid 2.1
Embryo fractions 6.4
Embryonic axis 2.2 0.6 38.5
Scutellum 6.8 1.5 53.3
Bran
Starchy endosperm 11.6 3.7
20.5 3.5
80 1.3
60 1.0

Note: The result represent the average of two leading oats cultivars (Dal and Froker) grown
in Wisconsin (USA).
Source: Adapted from Youngs (1972).

Δ7-stigmasten-3β-ol (6.4 %), cholesterol (5.8 %), campesterol (5 %) and
Δ7-cholesten-3β-ol (2.8 %) (Lásztity, 1998).

FFA range from 2 to 11 % of the total oat lipid (Sahasrabudhe, 1979),
and they are particularly important because of their involvement in the
production of off-flavours (hydrolytic rancidity). Their content increases
dramatically within a short time if the storage conditions, and in particular
the temperature and humidity, are not correctly monitored and maintained.
In fact, an increase in storage temperature and/or moisture content will
increase hydrolytic degradation. Additionally, the damage to the oat kernel
structure during harvesting or processing by grinding or flaking exposes the
kernel, leading to further susceptibility to the development of oxidative and
hydrolytic rancidity (Biermann et al., 1980).

Youngs et al. (1977) showed (Table 7.9) that palmitic, oleic, stearic and
linoleic acid are the major fatty acids present in the oat grain and together
account for more than 95 % of the total. Generally, fatty acids are homo-
geneously distributed among the bran and starchy endosperm in the free
lipid. In the bound lipid fraction, the same observation can’t be made for
myristic acid which was found to be unevenly distributed between the bran
(1.6 %) and starchy endosperm (0.6 %). Other fatty acids identified
in some oat varieties include lauric, palmitoleic and arachidic acids
(< 0.1 %) (Frey and Hammond, 1975), the series of unsaturated C20 acids
from 20:1 to 20:5 (0.5–3.0 % in total) (Sahasrabudhe, 1979) and traces of
lignoseric and nervonic (24:1) acids (Zhou et al., 1998b).

Unlike wheat and maize, oat starch contains greater amount of lipids,
existing as an amylose – lipid complex, ranging from 1 to 3 % (Sowa and
White, 1992; Gibinski et al., 1993). Morrison identified three categories of
lipids that are experimentally distinguishable – internal lipids or true ‘starch

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264 Cereal grains for the food and beverage industries

Table 7.9 Concentration of fatty acid and their distribution in oat kernel, average
of two cultivars

Fraction Fatty acid composition (%)

Myristic Palmitic Stearic Oleic Linoleic Linolenic
(14:0) (16:0) (18:0) (18:1) (18:2) (18:3)

Free lipids 0.4 18.8 2.2 39.4 37.9 1.3
Kernel 0.4 18.1 1.9 38.4 39.6 1.6
Bran 0.6 18.9 2.3 37.4 39.4 1.4
Starchy endosperm 0.6 21.1 1.2 34.5 39.7 2.8
Scutellum 0.9 21.6 1.9 28.8 42.5 4.1
Embryonic axis
0.9 25.7 2.0 28.8 41.0 1.4
Bound lipids 1.6 25.7 1.6 27.2 42.2 1.4
Kernel 0.6 27.3 2.4 28.4 39.7 1.4
Bran
Starchy endosperm

Source: Adapted from Youngs et al. (1977).

lipids’, surface lipids and non-starch lipids. The internal lipids reside within
native starch granules, either in the cavity of the amylose helix or in the
spaces between amylose and amylopectin (Morrison, 1981). The surface
lipids include those that are attached to the surface of the starch granules
in situ or become attached during the isolation of starch and largely influ-
ence the performance of the starch in terms of viscosity and gelatinization
properties (Morrison, 1978).The remaining non-starch lipids, mainly derived
from endosperm, aleurone and germ, can reside either in a free state or
bound with proteins on the starch granule surface.

7.3.3 Minerals
The mineral content of oats is generally 2–3 % and, as in other cereals, the
main mineral components are dominated by P and K, with lesser amounts
of mg and Ca (Table 7.10). Frølich and Nyman (1988) investigated the
mineral contents of different oat fractions. In the husk, minerals were
mostly (~ 97 %) present in the insoluble fibre fraction (50 % of the Si and
30 % of the K), while in the kernel, most (~ 70 %) of the minerals were
associated with the soluble fibre components (> 50 % of the Ca, Fe, Mn and
P), probably the β-glucans and/or the phytate (myoinositol hexaphosphate).
Fe and Cu were the only minerals that were found to any greater extent in
the insoluble fibre fraction in the kernel (~ 20 %). In the soluble fibre frac-
tion, most of the phytate (> 90 %) was found. Phytate, alongside the fibre,
is responsible for impairing Fe and Zn availability in humans (Sandstrom

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Table 7.10 Mineral compositions of oat and other cereal grains

Minerals Composition (mg/100 g)
Oats Wheat Barley Rye Rice Corn Sorghum

Manganese (Mn) 5 5.5 1.8 7.5 6 0.6 1.5
Copper (Cu) 0.4 0.8 0.9 0.9 0.3 0.2 0.5
Iron (Fe) 7 6 6 9 2 6
Magnesium (Mg) 140 180 140 130 90 140 150
Calcium (Ca) 95 60 90 70 68 30 20
Potassium (K) 460 580 630 520 340 330 400
Phosphorus (P) 340 410 470 380 285 310 405

Source: Adapted from Hoseney et al. (1981).

et al., 1987; Marklinder et al., 1995). However, during food processing and
digestion, phytate may be degraded to inositol phosphates with a lower
phosphorylation degree, thus reducing the adverse effect of phytic acid on
mineral absorption.

A study conducted by Reale et al. (2007) into the importance of lactic
acid bacteria (LAB) for phytate degradation during cereal dough fermenta-
tion reported that the optimum pH for phytate degradation was ~5.5. They
reported that 50 LAB strains, previously isolated from sourdoughs, did not
show significant intra- as well as extracellular phytase activity but provided
favourable conditions for the endogenous cereal phytase activity by lower-
ing the pH value.

7.3.4 Vitamins
Oat-based products contribute vitamins to the human diet, albeit in a
small concentration. Compared to other cereals, oats contain high level of
thiamin and pantothenic acid (Youngs and Forsberg, 1987; Matz, 1991).
Relatively high levels of vitamin E, riboflavin and folic acid can be also
detected (Welch, 2005). Table 7.11 shows representative values of vitamin
contents in oats and oat products, given as mg of vitamins per 100 g of dry
weight.

7.3.5 Minor components
Alongside the health-promoting β-glucan (Kelly et al., 2007), oat grains also
contain a wide range of minor components whose potential role in health
are not fully understood. Oats are rich in antioxidants including vitamin E,
avenanthramides, which are unique to oats, phenolic acids, flavonoids,

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266 Cereal grains for the food and beverage industries

Table 7.11 Vitamin contents of oat kernel, oat bran and oat hulls

Nutrients Vitamin content
(representative value per 100 g of fresh weight)

Oat kernel Oat bran Oat hulls

Vitamin E (mg) 1.60 3.30 –
Thiamin (mg) 0.70 1.10 0.15
Riboflavin (mg) 0.12 0.18 0.16
Niacin (mg) 0.9 0.9 1.04
Vitamin B6 (mg) 0.23 0.15
Pantothenate (mg) 1.1 1.0 –
Folate (µg) 60 37 –
Biotin (µg) 21 38 –
–

Sources: Compiled using data collected from Welch (2005), Matz (1991).

sterols and phytic acid.These compounds possess a phenolic moiety (Collins,
2011) with free-radical scavenging capabilities and thus exhibit antioxidant
properties in vitro (Emmons et al., 1999). Avenanthramides, low-molecular-
weight, soluble phenolic compounds (Peterson, 2001; Collins, 1989) are
mainly localized in the bran and subaleurone layers and at a concentration
of up to 300 ppm (Dimberg et al., 1993; Peterson, 2001), representing the
main phenolic antioxidants present in the oat kernel (Peterson, 2001). In
addition to their proven strong antioxidant activity in vitro and in vivo (Liu
et al., 2004; O’Moore et al., 2005), avenanthramides have also recently been
shown to exhibit anti-inflammatory (Liu et al., 2004), antiproliferative
(Meydani, 2009) and anti-irritant activity (Sur et al., 2008), which may
provide additional protection against CHD, colon cancer and skin irritation.
Other minor oat grain components which may exert important physiologi-
cal effects by a diversity of mechanisms includes saponins, sterols and
lignans (Ryan et al., 2007). An enzyme inhibitor which inhibits the activity
of trypsin was identified in oats although at low levels when compared to
barley and rye (Boisen, 1983). However, it is promptly digested by pepsin
and is thermolabile, so its antinutritive effect is practically negligible.

7.4 Oat milling

The earliest oat milling technologies were extremely primitive and remained
so until the latter part of the nineteenth century. Since the oat kernel is
enclosed in the hull, it must be removed before processing. Unlike barley
and rice, the kernel and hull are not fused together and thus hull can be
easily removed with minimal disruption to the kernel.

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Oats 267

7.4.1 Milling-oat specification
Oat milling-quality influences include groat percent, hectolitre weight, thins
and contaminant (physical, biological and chemical) levels. Groat percent
(proportion of groat to total grain weight including the hull) is one of the
most important quality characters for millers. Groat percent values greater
than 72 % are acceptable, but 75 % or higher are optimum. Test weight
(bulk density) is also a good parameter to predict the mill yield and is an
important consideration for shipping and handling. Test weight is signifi-
cantly influenced by the kernel and hull characteristics (Doehlert et al.,
1999; Peltonen-Sainio et al., 2004). To better classify the milling quality of
oats, Hutchinson (1953) proposed to use the thousand-grain weight method
in substitution of the test weight that represents, as stated by the authors, a
rough index of the ‘millable’ grain.

Two other important quality considerations for oat products are con-
tamination by wheat, barley and rye for CD patients and Fusarium species
mycotoxin contamination which is a concern for all consumers (Wrigley
and Batey, 2010). The amount of contaminating non-oat grains in a batch
is critical for the miller as it is almost impossible to separate oats from
barley due to their similar shape.The level of thins is also another important
parameter for the oat milling-quality specification. It is defined as amount
of oats that pass through 2 -mm slotted screen. An upper limit of 10 % for
thins has been suggested by Webster (1996), although a percentage of 5 %
or less is a much more realistic target value (Noël and Webster, 2011). A
further important factor for oat grain quality is the content of FFA. It is an
indicator of kernel damage, and high levels of FFA lead to development of
unpleasant aromas (rancidity) and flavours in the final products.

7.4.2 Oat storage
Oats, like other grains, are sensitive to their storage environment. Oats can
be stored for ca. one year in good facilities maintained under storage condi-
tions of 20 °C and 12–14 % moisture with adequate protection against
insects, rodents (Ganssmann, 1995) and fungi. Storage at moisture levels
higher than that will cause the development of hot spots which leads to
rapid deterioration of oat quality and boosting of the lipid hydrolytic system
with consequent rapid increase in FFA content (Noël and Webster, 2011).

7.4.3 Milling and processing operations
Milling and processing operations are illustrated in Fig. 7.5.The pre-cleaning
process is normally utilized as a first step contaminant removal to prevent
mill damage. It aims to separate foreign materials such as weed seeds, straw,
stones, metal particles and dust using an aspirator (to remove the light
impurities), a separator (to remove straw and stones) and a magnetic sepa-
rator (to remove iron and steel). After the cleaning process, oat grains pass

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268 Cereal grains for the food and beverage industries

Oat intake

Precleaning

Storage

Cleaning

Grading

Hulling

Hull, fines and Hull, fines
groat separation

Kilning

Dry groat
grading

Cut groats Broken or small Large groats Grinding
groats Flaking Oat flour

Cutting Premium oat flakes

Milling Flaking

Oat bran/oat flour Fast cooking oats

Fig. 7.5 Flow diagrams of oat intake pre-cleaning, cleaning and grading
processes.

through the grading system encompassing a series of screens of different
sizes that are subjected to rotary or oscillating motion. This step separates
clean oat grains into two to four fractions based on kernel density, length
and weight. Even in this milling step, some forms of magnetic separators
are included at the entrance to the grading system.

The hulling process is the next step; here groats are separated from the
hull using either impact or stone-hulling systems. At this phase, the miller
aims to maximize hulling efficiency while minimizing groat breakdown

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