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(Noël and Webster, 2011). Hulls and fines are separated from whole groats,
broken groats and unhulled oats. Some data indicate that kernel moisture,
β-glucan, and protein content may have an effect on the amount of break-
age (Engleson and Fulcher, 2002) and in determining ease of dehulling
(Ganssmann, 1995). Further refinement occurs when groats are separated
from this mixture based on physical characteristics, such as groat size and
weight. The recovered unhulled oats are then recycled back to the dehullers
(Noël and Webster, 2011).

After hulling the next step in the oat milling process is the heat-treatment
or kiln drying which has multiple beneficial results. Heat treatment stabi-
lizes the groats by inactivating lipase, lipoxygenase and peroxidase systems
that cause rancidity and bitterness in the final product. A pleasant nutty,
browned, toasted-oat flavour and slightly brown colour are also developed
(Marjatta, 2011). Additionally, the elevated temperature (up to 100 ˚C) and
low moisture reduce the bacterial and mould levels found on the surface
of the groats. On the other hand, the kilning process has been shown to
reduce the content (20–40 %) of heat-labile vitamin B1 (Noël and Webster,
2011).

After kilning, dried groat is subjected to cutting using a rotary granulator
consisting of a revolving perforated drum and a series of a stationary knives
mounted outside the lower half of the drum. During cutting, oat groats are
chopped into different pieces (two to four) with the size being influenced
by the initial grain size, groat moisture, knife sharpness and drum rotation
speed. At the end of the cutting step, a steel-cut groat mixture contains
various-size groat pieces, fines and uncut groats. If needed, a size separation
step can also be performed on the cut bulk. The residual fines and hull
pieces eventually present in the steel-cut groat mixture are removed using
an aspirator.

Further flaking occurs when tempered steel-cut groats are flattened
between two large rollers to produce oat flakes. Before flaking, a tempering
process is strategically performed to add 3–5 % moisture to the steel-cut
groats, which are characterized by a moisture content between 9 and 12 %,
to reduce the groat fragility (Noël and Webster, 2011). The flakes exiting
this process may go directly to the packaging line (fast cooking oats, oat
flakes) or be milled for producing oat flour and oat bran (Ganssmann, 1995)
(Fig. 7.5). Commercial processors generally can produce 100 kg of product
from 175 kg of oats. Milling efficiency varies according to the oat variety
and mill operating efficiency.

7.5 Food and beverage applications of oats

Oats have been part of the human diet in Europe since at least the first
century AD, when they were consumed as porridge, gruel and bread (Ran-
hotra and Gelroth, 1995). However, it was only in Ireland, Scotland and

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270 Cereal grains for the food and beverage industries

England that oat consumption persisted where oats are still used in por-
ridges, oatcakes, puddings, scones and leavened baked goods (Webster,
1986; Ranhotra and Gelroth, 1995; Welch, 1995). In order to produce
high-quality leavened bakery products, oats need to be blended with other
ingredients due to their lack of gluten. When compared to wheat, oats
contain less starch, one-third more protein and almost four times more fat
(Strychar, 2011). Two factors that have limited the use of oats for foods
historically are the whole-grain form of oats and the thermal processing
requirements. Despite these limitations, oats have found a wide range of
applications, mainly due to the growing demand for ‘healthy’ food products
following the approval, in 1997, of the health claim for oat-soluble fibre by
the US Food and Drug Administration (Strychar, 2011). Oats have found a
wide range of applications and are used in the production of hot cereals,
ready-to-eat breakfast cereals, bakery products, snack foods, cookies, infant
foods and other products.

7.5.1 Hot cereals
Hot cereal is the most popular food product made from oats and has found
its primary market in the USA, UK and Northern Europe. Products vary
from instant-cook oat flakes, usually fortified with minerals and vitamins,
combining a smoother texture and wide range of flavours, to the rolled oats
(whole oat flakes) where the flakes maintain their identity and texture.
Weetabix, Kelloggs and Quaker are some of the major companies that are
distributing hot oat breakfast cereals on the market (Webster, 1996).

7.5.2 Ready-to-eat cereals
Ready-to-eat cereals (RTE) represent the second biggest product for oats.
These products include muesli, puffed, flaked and extruded products. A
wide range of ingredients (dried fruit, malt, sugar, nutrients, flavouring) and
processes (toasting, rolling, puffing, shredding and extruding) may be used
in the production of RTE from oat mill products (Webster, 1996). Oat flour
can be blended with corn flour to produce an expanded RTE product (Liu
et al., 2000). Several companies hold the market of oat RTE, including Kel-
loggs, Purina, Quaker and Jordan.

7.5.3 Bakery products from oats
Oats and oat products are used in a wide range of bread and bakery prod-
ucts. However, because oats contain β-glucan and little or no gluten, it is a
technological challenge to produce bread with an acceptable volume and
texture quality using high levels of oats (Oomah, 1983). Several researchers
have attempted to incorporate oats into a wheat system to improve the
protein content of the bread (Oomah, 1983), to increase to soluble fibre

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content (Hager et al., 2011) or to use sourdough and hydrostatic pressure
(HP) technologies to improve the bread-making performance of oats
(Hüttner et al., 2010b, c). Generally, the incorporation of oat flour into a
bread formulation in concentrations higher than 25 % leads to a progres-
sive decrease in dough development time, dough strength, water retention
and loaf volume (Oomah, 1983). However, the level of wheat flour replaced
with oat flour is not the only parameter influencing the rheological proper-
ties and bread-making performance of the final bread. Hüttner et al. (2010a)
found a predictable relationship between the oat flour physico-chemical
properties and bread quality, whereby oat flour with coarse particle size,
limited starch damage and low protein content results in superior oat bread
quality. HP was also shown to improve the bread-making performance of
oat flour. In this regard, Hüttner et al. (2010b) revealed significant bread
improvement when oat batter, treated at 200 mPa, was included in the
bread formulation in concentrations up to 10 %. The weakening of the
protein structure, moisture redistribution and possible changed interactions
between proteins and starch were indicated as the factors responsible for
the positive effects of HP-treatment on the bread-making performance of
oat flour. Hüttner et al. (2010c) also investigated the potential of sourdough
fermentation in the production of high-quality oat bread. They found that
starting oat sourdough with autochthonous LAB improves texture and
loaf-specific volume, thus enhancing the oat bread quality. A significant
improvement of oat bread texture was also achieved by adding wheat
gluten to whole-grain flour (Salmenkallio-Marttila et al., 2004).

In gluten-free products, oats ensure a favourable aroma and taste as well
as texture. Recently, baking technology for 51–100 % oat bread has been
further developed (Flander et al., 2007) and the first products have already
been commercialized (see www.eho.fi for a 100 % oat bread) (Sontag-
Strohm et al., 2008).

7.5.4 Cookies
Oats and oat fractions have found a wide application in cookie production
(McKechnie, 1983) by affecting dough water absorption, flavour and texture
of the final products. In particular, dough spread factors increase with an
increasing amount of rolled-milled oat flour in the formulation, whereas
those cookies prepared with commercial oat flour remained constant
(Oomah, 1983).

7.5.5 Infant foods
Oats are a major component of infant foods due to their high nutritional
profile, lack of allergenicity, palatable flavour, good shelf-life, stability and
low cost (Shukla, 1975). Oat flour is also used as a thickener in many infant
foods (Webster, 1986; Ranhotra, 1995).

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272 Cereal grains for the food and beverage industries

7.5.6 Non alcoholic oat-based beverages
Fermentation of oat slurry provides a yoghurt-type product that can be used
by people suffering from CD, having an allergic reaction to milk, or who
are lactose intolerant (Sontag-Strohm et al., 2008). Several drinks contain-
ing oats have also emerged into the markets (Onning et al., 1998; Chronakis
et al., 2004) such as ‘Oat milk’® (Onning et al., 1998), ‘Oatrim’® (Pszczola,
1996), calorie-reduced yogurts fortified with oat fibre (Fernandez-Garcia
et al., 1998) and ‘ProViva’®, a product from an oatmeal fermented with
Lactobacillus plantarum (Bekers et al., 2001).

7.5.7 Alcoholic oat beverages
Barley is the most widely used cereal in beer production today, but it is very
likely that in the early days oats were also used (Buglass, 2011b). Today,
however, they have lost their significance in brewing (Meussdoerffer and
Zarnkow, 2009) since barley proved to be more suitable for these purposes.
Moreover, oats possess relatively large amounts of lipids that negatively
influence beer head retention (Buglass, 2011a). Oatmeal stout is brewed
with a small proportion of oats (5–15 %) (too much oats gives an astringent
taste). By the 1970s, English breweries had ceased brewing of oatmeal stout,
but the style was revived a few years ago by Sam Smith’s Tadcaster Brewery
(5 % ABV) (Buglass, 2011a). Today, only a few speciality beers (lagers, ales
and stouts) are still produced with unmalted and/or malted oats as flavour-
ing ingredients. In fact, as a brewing adjunct, oats can improve pleasant
flavour properties of the final product (Marjatta, 2011) as well as turbidity
stability (of top-fermented beers) (Meussdoerffer and Zarnkow, 2009).
Beers produced with up to 10 % oats showed a distinct toasted, biscuit-like
flavour and aroma combined with a relatively intense and creamy mouth-
feel (Taylor, 2000).

During steeping and germinating, oat grain absorbs water relatively
quickly (Briggs, 1998). Hence, a short steeping time followed by spraying
water on the seeds during germination are sufficient measures to achieve
the desired degree of steeping. The process conditions for the subsequent
germination process are similar to those applied for barley.

Oats are characterized by their high contents of fat and protein and
significant deficiency in α- and β-amylase, resulting in insufficient extract
recovery in comparison to barley (Belitz and Grosch, 1982; Meussdoerffer
and Zarnkow, 2009). In addition, oat grain is characterized by high β-glucan
content that can adversely affect the processability of mashes, worts and
beer due to an increased viscosity (Briggs, 1998). However, low β-glucan
oat varieties (e.g. Duffy) are perfectly suited for brewing (Meussdoerffer
and Zarnkow, 2009).

Worts from 100 % oat malt were comparable to barley malt worts, in
view of their physico-chemical properties. The former differ mainly by a

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higher content of zinc, β-glucan and tryptophan. Oat malt beers also exhibit
a distinct oat-typical flavour (Meussdoerffer and Zarnkow, 2009).

7.6 Conclusions

After a decline dating from the 1970s, world oat production seems to have
stabilized due to an increased consumer awareness of the heart-health
benefits of oat-soluble fibre. It is also useful for the control of diabetes and
lipid profile representing a good source of B-complex vitamins, proteins,
fats and minerals. Additionally, preliminary studies on avenanthramides
have pointed towards a link between oat components and regulation of
allergenic responses, asthma and proliferation of cancer cells. This may also
exert a further boost for the human food market for oats.

However, additional medical research must verify this possible relation-
ship between minor oat constituents and health benefits. Due to the great
genetic variability existing for key traits such as β-glucan, fat and proteins
in oats, plant-breeding could make significant progress in increasing levels
of the health-promoting components. At the same time, the development
of new food products served as either main or side dishes could consider-
ably expand oat utilization.

7.7 Future trends

Due to the increased consumer awareness regarding health and the role of
various foods in the improvement of quality of life, oats hold many oppor-
tunities for development as foods, feeds, industrial and pharmaceutical
products, which all add value to the oat crop. Oats represent a natural
functional food, providing several health benefits, including lowering blood
cholesterol, reducing risk of colorectal cancer and fighting obesity. This may
only be the ‘tip of the iceberg’ regarding the health benefits of oats as other
opportunities such as nutraceuticals production also exist. In nutraceutical
production, components are isolated and purified from grain and sold in
medicinal forms not usually associated with food products. Tailoring the
nutritional and functional components of the oat grain, depending on the
final qualities required, will support many novel and potential uses of this
crop. The increase of feed lots and the development of improved oat variet-
ies for feed value will also increase the demand for oats. Additionally, oat
grain production can potentially increase as they are easy to grow, work
well in crop rotation and have relatively low input costs. Increased con-
sumption in countries such as India and China is also anticipated to increase
demand for oats. In summary, the future of the oat crop looks undeniably
promising.

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274 Cereal grains for the food and beverage industries

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100.0 µm t n
p
(a) s
100.0 µm a

s

p
s

(b)

s se

e

(c)
Plate V (a) Confocal laser scanning microscope (CLSM) micrograph section of
the bran: p: pericarp, n: nucellus; a: aleurone layer; s: subaleurone layer. The portion
of the brand was stained with fluorescein isothiocyanate (FITC) for starch (green)
and with rhodamin B for protein (red). (b) CLSM micrograph of portion of starchy
endosperm; s: starch; p: protein. (c) CLSM micrograph portion of germ–endosperm
interface of transversal cross-section of the caryopsis, taken at the level of box C;

se: starchy endosperm; s: scutellum; e: embryo; t: trichomes (hairs).

© Woodhead Publishing Limited, 2013

8

Sorghum

DOI: 10.1533/9780857098924.283

Abstract: Sorghum (Sorghum bicolour subsp. bicolor) belongs to the family
Gramineae and is a C4 cereal grass. It is a major crop in the USA, India,
Argentina, Mexico, Africa, China and Australia. Sorghum is viewed as an
attractive raw material for wheat/gluten-free products due to the neutral flavour
and colour of specific varieties, its low allergenicity and its ability to grow in
drought-like conditions. It is also an important source of nutraceuticals due to its
high content of antioxidant phenolic compounds. Sorghum is used to produce a
wide range of food products such as whole-grain-type products, breads and
pancakes, dumplings and couscous, porridge, gruels, cakes, cookies, pasta, a
parboiled rice-like product, snack foods and beers. Exciting new niche markets
for sorghum could be developed by producing novel functional foods containing
antioxidant polyphenols, or using sorghum to develop novel lactose-free probiotic
beverages.

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

8.1 Introduction

Like rice and maize, sorghum is a C4 cereal grass and belongs to the family
Gramineae, subfamily Panicoideae and tribe Andropogoneae. All cultivated
sorghum species are diploid with 2n = 20 chromosomes and belong to one
species, Sorghum bicolour L. Moench, syn S. vulgare (Matz, 1991). This
includes diverse types of grain such as sorghum, broomcorn, sudangrass and
tall sorghum which is used as forage, silage or for sugar syrup production.
Sorghum originated in Africa some 3000–5000 years ago (Harlan, 1971).
After domestication, sorghum spread to India and from there to China, the
Middle East and Europe. Sorghum also reached the Western hemisphere
during the time of the slave trade (Matz, 1991). Today it represents a major
crop in USA, India, Argentina, Mexico, Africa, China and Australia (FAO/
UN, 2012). Sorghum is the fifth most important cereal crop in the world
after maize, rice, wheat and barley (FAO/UN, 2012) and, from a growth and
survival perspective, out-performs other cereals under various environmen-
tal stresses. In particular, in warmer temperatures and tropical regions of

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284 Cereal grains for the food and beverage industries

the world (Anglani, 1998b) sorghum excels due to its drought tolerance. In
many parts of Africa, Asia, Central America and the Middle Eastern Arab
countries, sorghum is the staple food and, in some countries, also serves as
the main source of beverages (Kent and Evers, 1994). More than 35 % of
sorghum grain production for human consumption is used to aid digestion
and relieve human constipation. The remainder is used as animal feed, in
alcohol production and as a raw ingredient in industrial products (Awika
and Rooney, 2004).

Sorghum protein is considered to be poor in quality due to its relatively
low content of essential amino acids, such as lysine, tryptophan and threo-
nine (Badi et al., 1990). The protein digestibility is also drastically reduced
after cooking (Axtell et al., 1981; Eggum et al., 1983). However, the protein
quality of sorghum can be successfully improved through malting technol-
ogy which causes an increased lysine content during germination (Dalby
and Tsai, 1976).

Sorghum, like the other cereals, is a good source of the B vitamins and
minerals such as potassium and phosphorus, while its calcium content is low
(Khalil et al., 1984). It also contains antinutrition factors such as poly-
phenolic compounds, concentrated in the pigmented testa of the sorghum
kernel (Obizoba, 1988), which are able to bind dietary proteins, digestive
enzymes, minerals and vitamins (Wang and Kies, 1991), thus rendering them
unavailable for mammalian assimilation in the gut.

The principal foods prepared with sorghum are tortillas, couscous,
porridges and baked goods made from composite flours containing
sorghum and millet (Badi and Hoseney, 1976). In the tropical regions,
baby foods are made from sorghum and maize gruels with the addition of
sugar (Obizoba, 1988). Amongst these ogi, which is a fermented sorghum
porridge, is the most important weaning food for babies (Dada and
Muller, 1983).

8.1.1 History, production area, price and yield
The timing and place of sorghum domestication are not fully known
although it is known to have commenced with early settled human life.
Vavilov (1926) identified the old Abyssinian (Ethiopian) area as the centre
of origin of sorghum while other authors have suggested a more broad area
(De Wet and Harlan, 1971) or separate centres of origin for different species
(Snowden, 1935). However, it is generally agreed that S. bicolour originated,
and was domesticated, in the Sub-Saharan region of Africa and subse-
quently spread to India and China (Henzell and Jordan, 2009).

Over 700 million hectares of the world’s surface is reserved for cereal
cultivation. Of this, only some 42 million hectares is sorghum (Table 8.1).
Over 65 % of this is in developing countries; however, the USA is the largest
producer (8.7 million tonnes in 2010). The next largest producers are
India and Mexico with 6.9 million tonnes each (FAO/UN, 2012). World

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Table 8.1 Sorghum and total global cereal grain production from 2000–2010

Total sorghum Total cereal Sorghum as Area sorghum Sorghum

Year production production % of total harvested yield

(Mt) (Mt)a crop grains (Mha) (t/ha)

2000 55.60 2044 2.72 40.90 1.36
2001 59.60 2093 2.85 43.40 1.37
2002 53.30 2077 2.57 41.00 1.29
2003 58.80 2260 2.60 44.30 1.32
2004 57.80 2247 2.57 40.50 1.42
2005 59.80 2219 2.69 46.20 1.29
2006 57.60 2335 2.47 42.90 1.34
2007 62.30 2503 2.49 44.30 1.40
2008 66.20 2470 2.68 45.00 1.47
2009 56.20 2472 2.27 40.30 1.39
2010 55.60 2412 2.31 40.50 1.37
Average 58.44 2285 2.56 42.66 1.37

aTotal cereal production includes corn, rice, wheat, barley, sorghum, millet, oat, rye mixed grain.
Mt = millitonne
Source: Data from FAO UN (2012).

production of sorghum has increased from 40 million tonnes, at the begin-
ning of the 1960s, to 65 million tonnes during the mid-1970s, after which
growth fell back to 56 million tonnes in 2000 (Table 8.1).The primary reason
for the contractions in sorghum production is thought to be African droughts
(Dendy, 1994a).

In the last 10 years, the maximum planted area for sorghum was reached
in 2008, when 45 million hectares were seeded. It was also in 2008 that the
maximum amount of sorghum yield was achieved, which amounted to
approximately 66 million tonnes and 1.47 tonnes/ha (Table 8.1). Nowadays,
sorghum represents less than 3 % of world cereal production (FAO/UN,
2012). This places sorghum fifth in quantitative importance among cereals,
ranked after corn, rice, wheat and barley.

Production is spread very unevenly around the globe with Africa (Sudan
and Nigeria) and Asia (India) having the largest areas harvested. Sorghum
is also widely grown as a staple food crop in the drier parts of Central and
South America (Colombia, Venezuela and North-Eastern Brazil).

In the developed countries, led by the USA, where sorghum is primarily
used as a feed grain, an intensive breeding programme, the application of
large quantities of fertilizer and the advancement of agricultural practices
(pest control, seed bed preparation) have maximized the attainable yield
that reached 4.5 tonnes/ha in 2010. This is five times that for developing
countries such as sorghum producers in Africa (0.84 tonnes/ha in 2010)
where this grain is almost entirely used as a staple food. Notwithstanding
its poor yield, sorghum plays a fundamental role in rural food security in
the semi-arid tropical areas that represent home for billions of people. The

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286 Cereal grains for the food and beverage industries

importance of sorghum in these areas is illustrated by the fact that it rep-
resents more than 70 % of total cereal production in some states of Africa
(Sudan, Burkina Faso, Niger, Botswana) (FAO/UN, 2012). With regard to
sorghum producer price, in some countries such as Kyrgyzstan, Mozam-
bique, Guinea-Bissau, Ethiopia and Yemen, the price increased between
three- and five-fold between 2000 and 2009 (Table 8.2), reaching values up
to 800 US $/tonne, while in the USA the increase was less than two-fold
and, at 130 US $/tonne amongst the lower producer prices.

8.1.2 Phytology, classification and cultivation
Harlan and Dewet (1972) classified sorghum as being of two major taxa, S.
bicolour subsp. Bicolor (cultivated) and S. bicolour subsp. Arundinaceum
(spontaneous). All cultivated sorghum belongs to one species, S. bicolour
L. Moench, syn. S. vulgare which comprises an extremely variable group of
cultivated and wild type races (five) and intermediate races (nine) (Doggett,
1988). Sorghum can be categorized usefully according to its end-use, such
as: grass sorghum, with fine leaves and stems used for hay and pasture;
forage sorghum, with tall stems used for fodder and forage; sweet sorghum,
with juicy leaves and stems used for sugar, syrup and alcohol production;
and grain sorghum, with short stems (suitable for mechanical harvesting)
and grown for its seeds which are suitable for food and feed applications.
The US Grain Standards Act has classified different sorghums in terms of
their tannin contents: ‘Sorghum’, ‘Tannin sorghum’, ‘White sorghum’, and
‘Mixed sorghum’. The ‘Sorghum’ class does not contain more than 3 %
tannin sorghum with a pigmented testa or undercoat. The ‘Tannin sorghum’
class has a pigmented testa (subcoat) and contains not more than 10 % of
kernels without a pigmented testa. The ‘White sorghum’ class lacks a pig-
mented testa and contains no less than 98 % kernels with a white pericarp,
and no more than 2 % of sorghum of other classes (USDA, 2007). However,
the use of colour as a classification for tannin content should be avoided as
grain colour is not an accurate indicator of tannin content.

This crop is ideally suited for semi-arid agro-climatic regions, but grows
better under irrigation in dry areas (Matz, 1991). Sorghum is widely grown
on all types of soils, in particular sandy soils because of their water infiltra-
tion and retention characteristics (Matz, 1991). Cultivation practices for
sorghum are generally similar to those used for other cereals like corn and
millet and have a large impact on crop yield. In countries such as the USA,
high-yielding hybrid cultivars and large-scale mechanized farming results
in a yield of 4.5 tonnes/ha. Conversely, in some regions of Africa, where a
small-scale production using traditional manual farming practices is widely
performed, the yield is only 0.8 tonnes/ha (FAO/UN, 2012). Sorghum is also
vulnerable to attack by various bacteria, fungi, virus, nematodes and insects
(Frederiksen, 1986); however, these pests rarely cause devastating losses,
although some may be severe locally.

© Woodhead Publishing Limited, 2013

Table 8.2 Producer prices (US $/tonne) of sorghum from 2000–2009

Crop year

Country

2000 2001 2002 2003 2004 2005 2006 2007 2008 2009

Republic of Korea 1080.7 984.5 1015.9 1066.6 1132.6 2524.9 2237.6 2502.2 2522.0 2558.8
Guinea-Bissau 351.1 341.0 358.7 430.1 710.8 854.6 934.1 1138.2
Sri Lanka 341.7 294.4 340.3 348.4 402.0 402.2 507.1 556.0 1287.9 1235.1
Yemen 228.8 266.8 287.0 275.3 335.5 346.2 355.6 434.2
Malawi 500.6 411.2 519.0 565.5 507.9 514.4 535.9 595.1 926.1 883.0
Eritrea 284.7 264.4 278.0 328.1 396.1 391.7 449.3 496.0
Dominican Republic 151.0 146.1 248.7 617.2 475.8 387.0 528.8 530.4 636.6 770.5
Ethiopia 142.1 101.1 90.5 166.6 160.6 188.7 173.6 345.3
© Woodhead Publishing Limited, 2013 Kenya 204.1 186.5 240.6 276.4 291.0 331.8 294.8 181.7 661.0 753.2
Ghana 153.1 242.5 242.8 216.1 264.4 424.4 362.7 350.2
Burundi 374.7 294.7 269.7 199.1 378.7 324.2 405.1 407.4 571.0 657.5
Rwanda 211.0 198.7 159.6 136.7 134.1 138.8 285.3 311.1
Togo 140.5 178.7 215.2 153.1 214.2 364.6 231.6 236.1 509.4 489.5
Honduras 183.9 177.1 167.5 158.9 151.4 149.5 162.4 225.3
Morocco 218.3 244.2 265 258.0 290.0 292.5 326.5 342.1 446.4 487.9
El Salvador 221.1 203.2 134.9 194.6 212.0 172.0 222.0 279.2
Sudan 165.6 192.1 107.3 137.5 143.6 335.2 243.0 178.9 197.6 472.1
Pakistan 129.5 115.6 134.0 170.6 170.0 168.0 237.3 284.8
Republic of Moldova 184.1 150.2 108.5 195.1 204.2 168.2 180.5 309.0 514.9 469.5
Côte d’Ivoire 2103.1 317.9 334.3 298.0 331.3 336.6 334.1 313.4
Nigeria 190.3 377.1 342.4 236.0 274.6 509.0 381.4 320.7 430.5 439.5
China 108.5 129.0 91.5 133.8 118.7 118.4 157.7 231.4
Colombia 173.9 179.9 165.4 156.5 176.5 191.6 205.1 254.6 388.5 434.1
Nicaragua 152.6 136.8 120.5 106.8 124.8 157.8 176.2 222.1
Russian Federation 169.7 168.4 122.4 172.9 246.5 194.3 246.7 336.0 629.7 378.0
Venezuela 179.4 184.2 144.8 203.8 205.0 196.2 215.1 210.9
Gambia 129 156.8 246.0 179.5 247.4 334.3 221.2 274.5 308.4 373.4
Namibia 157.4 154.8 123.3 253.1 277.9 263.2 271.0 283.9
Egypt 184.0 161.3 147.1 119.6 174.1 186.7 191.9 292.1 384.5 370.6
Romania 75.9 71.5 98.2 321.1 274.2 199.9 196.1 363.7
336.4 317.7

329.7 312.7

312.5 309.7

395.3 297.3

325.4 293.4

370.2 290.8

263.4 285.5

335.7 277.0

285.8 273.8
393.9 273.8

253.2 273.1

316.4 272.8

244.4 262.2

264.3 251.4

428.6 248.8

(Continued)

Table 8.2 Continued

Crop year

Country

2000 2001 2002 2003 2004 2005 2006 2007 2008 2009

© Woodhead Publishing Limited, 2013 Cameroon 313.8 171.9 180.8 206.5 210.4 217.0 228.5 247.0 269.4 247.5
Mali 87.4 75.0 124.8 165.2 111.8 233.6 183.8 179.7 218.8 235.7
Burkina Faso 84.3 141.9 159.3 154.9 174.9 178.7 187.3 193.8 225.3 217.8
Mozambique 51.8 79.7 105.6 92.5 111.2 141.3 177.3 174.5 205.8 216.4
Peru 151.9 131.2 88.2 140.9 137.5 142.6 128.3 201.5 198.3 215.9
Jordan 138.5 191.8 203.2 196.2 231.9 241.9 279.3 166.3 309.4 211.3
Panama 176.0 176.0 176.0 176.0 176.0 176.0 176.0 198.0 198.0 205.1
Bulgaria 67.3 63.6 70.3 90.6 177.3 120.3 104.0 173.8 207.2 201.4
Algeria 131.5 128.2 124.2 133.2 151.6 160.8 176.8 198.0 221.7 197.1
India 121.0 107.9 112.3 117.8 120.6 134.6 171.0 136.2 197.7 193.6
Spain 130.0 126.8 120.5 165.9 172.8 166.9 188.0 271.5 242.0 189.9
Belize 140.0 160.5 187.5 154.5 158.8 160.7 165.4 173.0 179.7 179.1
South Africa 74.9 88.3 142.3 191.7 139.7 177.1 210.7 214.7 179.0
Croatia 63.6 131.5 118.6 159.0 216.8 70.9 153.5 191.0 282.1 170.9
Israel 120.2 118.9 111.9 109.8 110.5 120.2 110.1 120.6 172.8 170.5
Thailand 74.8 63.9 75.9 92.3 108.7 109.3 141.6 183.5 135.4 170.1
Guinea 179.4 202.1 193.2 192.2 189.3 100.5 120.5 148.0 139.4 164.1
Australia 71.3 74.5 94.0 133.0 117.1 120.7 107.7 178.6 216.4 162.7
Hungary 82.6 143.5 118.1 173.2 219.4 102.4 131.8 201.3 237.7 160.9
Mexico 111.2 106.1 123.7 120.2 117.8 165.2 143.7 176.1 207.6 160.1
Niger 77.3 83.2 94.7 101.5 114.3 109.8 119.7 134.1 154.2 153.9
France 104.7 106.2 97.9 138.0 128.6 117.4 157.7 220.8 206.5 143.1
Uruguay 103.4 62.8 80.8 90.1 108.2 124.8 119.5 131.1 199.5 135.8
Kyrgyzstan 26.8 43.3 46.1 50.7 49.3 90.2 89.0 151.2 153.1 133.6
USA 74.0 76.0 91.0 94.0 70.0 74.9 130.0 160.0 126.0 130.0
Lebanon 169.7 167.3 159.1 127.3 123.6 73.0 126.7 123.3 132.3 119.7
Argentina 65.0 63.0 64.3 62.7 65.7 119.4 67.1 110.5 124.0 97.3
Brazil 68.3 42.4 32.5 32.2 30.5 51.0 34.0 40.1 51.8 42.4
Bolivia 41.1 34.8 32.5 41.2 39.9 31.0 41.9 45.1 51.1 40.5
39.5

Source: Data from FAO/UN (2012).

Sorghum 289

Fig. 8.1 Sorghum grains.
8.1.3 Structure of the sorghum kernel
Sorghum grains (Fig. 8.1) are generally spherical or spindle shaped and may
be coloured white, red, yellow or brown. The terms ‘soft’ and ‘hard’ have
been used to designate vitreous and opaque areas of sorghum endosperm,
respectively. Grain hardness plays an important role when dry milling
sorghum. The sorghum kernel is a naked caryopsis. It consists of three ana-
tomically distinctive regions, the pericarp (outer layer), the endosperm
(starch storage structure) and the germ (embryo) (Fig. 8.2a) (Dendy, 1994b).
The endosperm may be further subdivided into the subaleurone layer, cor-
neous or glassy endosperm, and the floury endosperm. In Fig. 8.2b, the
central floury endosperm and the outer vitreous endosperm are clearly
illustrated (Dendy, 1994b).

The pericarp contains a cuticle comprising layers of waxy materials and
is divided into three histological tissues: the epicarp, mesocarp and endo-
carp (Earp et al., 1983). The epicarp is two or three cells thick and consists
of rectangular cells often containing pigmented material. Unlike other
cereals, the sorghum mesocarp may contain starch granules. The endocarp
is mainly composed of cross and tube cells. Some sorghum varieties have a
layer of pigmented cells under the pericarp called the testa or undercoat
that can cause problems in processing. However, the undercoat can be lost
through breeding procedures (Hoseney et al., 1974).

The endosperm tissue is composed of the aleurone layer, peripheral,
corneous and floury areas. The aleurone layer is the outer cover (Fig. 8.2a).
It consists of single layer of rectangular cells adjacent to the testa or tube

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290 Cereal grains for the food and beverage industries

Aleurone layer

Pericarp Testa
Corneous endosperm
Cutin

Floury endosperm

Germ
(a) Hilum

5 kV ×18 1 mm AMRF, UCC

(b)

Fig. 8.2 Schematic representation (a) and scanning electron microscope (SEM)
micrograph (b) of the longitudinal section of sorghum kernel.

cells (Serna-Saldivar, 1995). The cell possesses a thick cell wall, large
amounts of protein, ash and oil. The peripheral endosperm tissue is com-
posed of several layers of dense cells containing large amounts of protein
and small starch granules (Sullins and Rooney, 1974, 1975). The corneous
and floury endosperm is composed of starch granules, a protein matrix,

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Sorghum 291

5 kV ×1,000 10 μm AMRF, UCC
(a)

5 kV ×1,000 10 μm AMRF, UCC

(b)

Fig. 8.3 SEM micrograph of the centre located floury (a) and outer glassy region
(b) of the sorghum endosperm.

protein bodies and cell walls rich in β-glucan and hemicellulose. Sorghum
shows a blue autoflorescence in the cell walls of pericarp, aleurone and
endosperm, which is mainly due to its ferulic acid content. In the corneous
endosperm, the protein matrix has a continuous interphase with the starch
granules and protein bodies embedded in the matrix (Seckinge and Wolf,
1973; Hoseney et al., 1974). The protein bodies are largely circular and vary
from 0.4 to 2.0 μm in diameter. The starch granules are polygonal (Fig. 8.3a,
b) and often contain dents from the protein bodies. Their size varies from
4 to 25 μm (average around 15 μm) (Taylor et al., 1984b).

The centre of the endosperm is floury. Here, the packing of the starch
and proteins is less tight and there is air spaces present that result in

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292 Cereal grains for the food and beverage industries

Table 8.3 Approximate composition of sorghum and other cereal grains

Components (g/100 g Sorghum Wheat Barley Corn Brown rice
edible portion)

Starch 50 61.8 51.4 59.3 69.1
Protein
Lipids 8.3 10.6 9.3 9.8 7.3
Crude fibre
Ash 3.9 1.9 2.8 4.9 2.2
Phytic acid
Tannin 13.8 10.5 16.4 9.0 3.3

2.6 1.4 1.7 1.4 1.4

1.0 1.0 1.1 0.9 0.9

1.6 0.4 0.6 0.4 0.01

Source: Based on data of Juliano (1999).

diffraction of the incoming light, giving an opaque or chalky appearance
under scanning electron microscopy (Dendy, 1994b).

The embryo is embedded in the sorghum kernel rendering it difficult to
remove (Rooney and Sullins, 1969). It consists of two major parts: the scu-
tellum and the embryonic axis. The scutellum represents the reserve tissue
containing high amounts of oil, protein, enzymes and minerals which func-
tion as a connector between the endosperm and germ. The embryonic axis
contains the new plant and is divided into a radicle and plumulae (Dendy,
1994b).

8.2 Chemical constituents of the sorghum kernel

The chemical composition of the sorghum kernel varies considerably and
is primarily dependent on genetic and environmental factors. The outer
layers, representing the pericarp, are rich in fibre. The endosperm contains
mostly starch and protein with low amounts of fat and fibre, whereas the
embryo is particularly rich in crude protein, fat and ash. The nutrient com-
positions of sorghum and other cereal grains are reported in Table 8.3. Even
though the reported sorghum protein content is relatively low, its variability
is higher than that of other cereals and may range between 8 and 16 %
(Juliano, 1999).

8.2.1 Carbohydrates
Sorghum contains non-structural (starch, sugars and fructosan) and struc-
tural carbohydrates (cellulose, hemicelluloses and pectic substances). Starch
is the chief sorghum non-structural carbohydrate and represents the main
source of energy required for germination. Some 50–75 % of total sorghum
grain weight is starch which is made up of straight-linked amylose chains
(glucose unit held together by α (1–4) glycosidic bonds) and branched

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Sorghum 293

amylopectin chains (glucose units held together by α (1–4) and α (1–6)
bonds). In the native form, they are considered to be pseudo-crystals that
have crystalline and amorphous areas. They are insoluble in cold water,
swell reversibly, rotate the plane of polarized light and are relatively inac-
cessible to enzymatic hydrolysis (Serna-Saldivar and Rooney, 1995). Starch
resides mainly in the endosperm distributed between both the central floury
(Fig. 8.3a) and the outer glassy regions (Fig. 8.3b). The size of sorghum
starch granules ranges from 2 to 30 μm with the typical size appearing in
the 10–16 μm range (Taylor and Belton, 2002).

Granules present in the corneous endosperm are small and angular,
whereas those in the floury endosperm are relatively larger and round.
Corneous endosperm starches have a lower iodine-binding capacity and
higher gelatinization temperature and intrinsic viscosity when compared
with starch isolated from the floury endosperm (Cagampang and Kirleis,
1985). The gelatinization temperature range for sorghum starch has been
determined by differential scanning calorimetry (DSC) to be 71–80 °C
(Sweat et al., 1984). The gelatinization temperature can also be followed by
loss of bifringence under a hot stage microscope (Hallgren, 1985). Gelati-
nization temperature ranges are affected by the amylose/amylopectin ratios.
Waxy starches (only amylopectin) have slightly higher initial and end-point
gelatinization temperatures than non-waxy starches. Initial and end-point
temperature ranges for waxy starches were 63.0–65.2 °C and 72.1–73.4 °C
while the initial and end-point temperature ranges for non-waxy starches
were 63.0–63.8 °C and 70.8–71.9 °C, respectively (Freeman et al., 1968).
When comparing starches isolated from the vitreous and floury parts of the
endosperm of the same sorghum variety, the vitreous endosperm starches
exhibit a slightly higher gelatinization temperature than the floury endo-
sperm starch (Cagampang and Kirleis, 1985). In addition, a much higher
paste viscosity has been observed for the soft endosperm flours than for the
hard endosperm flours using a Brabender visco-amylograph. In sorghum,
grain gelatinization may be restricted, and the digestibility of sorghum starch
may be lower than that of other starches, even in low-tannin sorghum
(Shelton and Lee, 2000). This low starch digestibility is possibly due to the
interaction between protein bodies and starch granules, suggesting that an
interference arises from a complex which may be formed, thus restricting
access to both starch and protein simultaneously (Taylor and Belton, 2002).

The primary sugars present in the sorghum grain are the monosaccharides,
glucose and fructose, the disaccharides, sucrose and maltose, and the trisac-
charide, raffinose (Nordin, 1958). Mature sorghum kernels contain 2.2–
3.8 % soluble sugar, 0.9–2.5 % free reducing sugar, 1.3–1.4 % non-reducing
sugar. Free glucose and fructose levels range from 0.6 to 1.8 % and 0.3 to
0.7 %, respectively. The bound glucose and fructose contents range from 0.7
to 1.2 % and 0.1 to 0.6 %, respectively (Bhatia et al., 1972; Anglani, 1998a).

Most of the sorghum fibre is located in the pericarp and endosperm cell
walls and is mainly constituted of cellulose, hemicellulose, lignin, pectin and

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294 Cereal grains for the food and beverage industries

gums. The majority of the fibre in sorghum is insoluble (86.2 %). Sorghum
contains 1.1–1.2 % soluble fibre, hemicellulose and cellulose, 6.5–7.9 %
insoluble fibre, 1.1–1.23 % of soluble β-D-glucan, and 1.3 % pentosans
(located mainly in the pericarp) (Knudsen and Munck, 1985). Approxi-
mately 70 % of the pentosans are alkali-soluble, and 30 % are water-soluble.
Insoluble dietary fibre increases during food processing due to increased
levels of bound protein, mainly kafirins, and enzyme-resistant starch. In
‘Tannin sorghum’, cooking also forms polyphenol–protein complexes, which
increases the grain bulking ability (Waniska et al., 2004).

8.2.2 Proteins
Sorghum grain protein content varies from 6 to 18 %, with an average of 11 %
(Lasztity, 1996). However, its content and compositions can vary substantially
depending on agronomic conditions (water availability, soil fertility, tempera-
ture and environmental conditions during grain development) and genotype.
Approximately 80, 16 and 3 % of the sorghum protein is located in the endo-
sperm, germ and pericarp, respectively (Taylor and Schussler, 1986). Sorghum
endosperm protein contains a large percentage of prolamine (aqueous
alcohol-soluble fraction) but is lacking in the essential amino acid lysine
(Jones and Beckwith, 1970). The endosperm contains the glutelins and kafi-
rins (the sorghum prolamin proteins) that represent about 80 % of the total
protein fraction in sorghum (Taylor et al., 1984a), whereas the lysine-rich
protein fractions, albumins and globulins, predominate in the germ (Waniska
et al., 2004). Kafirins are mainly located within the protein bodies and increase
in correspondence with total kernel protein levels (Warsi and Wright, 1973).

The sorghum kafirins can be categorized into three main classes –
α, β and γ – based on molecular weight and solubility. These fractions are
similar to the zein sub-fractions of corn (Shull et al., 1991). Depending on
whether it is floury or vitreous, the sorghum endosperm contains about
66–84 % α-kafirin, 8–13 % β-kafirin and 9–21 % γ-kafirin (Belton et al.,
2006). α-Kafirins are rich in glutamic acid and have a molecular weight of
22–25 kDa. β-kafirins have a lower molecular weight (approximately 18 kDa)
and are richer in the sulphur-containing amino acids, methionine and cys-
teine, which are found in monomeric and polymeric forms. The γ-kafirins
have a molecular weight of approximately 20 kDa and are rich in the amino
acids proline, cysteine and histidine. These sub-units are found as oligomers
and polymers. Both β and γ-kafirins form intermolecular and intramolecular
disulfide bonds which are highly cross-linked (Belton et al., 2006).

Kafirins are primarily located in spherical protein granules, with an
average diameter of about 2 μm in diameter (Taylor et al., 1984b) and are
tightly packed within a protein network, embedded in a glutelin protein
matrix and enclosed by starch granules. The outer ‘shell’ of protein bodies
is mainly composed of cross-linked β- and γ-kafirins, and has an interior
comprising predominantly α-kafirin (Duodu et al., 2003).

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Sorghum 295

Table 8.4 Amino acid composition of sorghum and wheat and daily recommended
levels of essential amino acids for adults

Amino acid, Sorghuma Wheat grainb FAO/WHO/UNU
(g/100 g protein) adults recommendationc

Essential 2.6 1.2 1.5
Histidine 4.0 4.2 3.0
Isoleucine 13.1 7.6 5.9
Leucine 2.6 2.9 4.5
Lysine 1.7 1.9 1.6
Methionine 1.4 2.3 0.6
Cysteine 4.4 5.3 1.9
Phenylalanine 3.3 3.3 –
Tyrosine 3.5 2.7 2.3
Threonine 5.6 4.5 3.9
Valine
8.8 3.8
Non-essential 3.6 4.8
Alanine 7.4 5.4
Arginine 19.7 32.5
Aspartic 4.1 4.4
Glutamic 8.8 10.8
Glycine 3.9 3.5
Proline
Serine

a Adapted from Haikerwa and Mathieso (1971).
b Adapted from Jensen and Martens (1983).
c FAO/WHO/UNU (2007).

An important feature of the sorghum proteins is their low digestibility
compared to other cereal proteins. It is proposed that protein cross-linking
may be the greatest factor that influences sorghum protein digestibility. This
may be between γ- and β-kafirin proteins at the protein body periphery,
which may impede digestion of the centrally located major storage protein
(Duodu et al., 2003). Moreover, other studies highlighted how the low
digestibility of the sorghum protein is reduced during high-moisture cooking
(Taylor and Belton, 2002). Furthermore, unlike wheat proteins, sorghum
proteins are not highly functional. Concentration and/or modification of
sorghum proteins (alkaline extraction, reducing agents, enzymatic hydroly-
sis, deamidation, irradiation and extrusion) could be one way to address this
challenge (Duodu et al., 2003).

With regard to amino acids (Table 8.4), sorghum is usually high in glu-
tamic acid, leucine, alanine, proline and aspartic acid (Hoseney et al., 1981).
From a nutritional point of view, lysine and threonine represent the first
and second most limiting amino acids in sorghum proteins, from a human
nutrition perspective. Sorghum lysine meets ~40 % of the recommended
daily/portion level for infants (Waniska et al., 2004).

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296 Cereal grains for the food and beverage industries

Sorghum and coeliac disease
Sorghum is a safe cereal grain for coeliac patients because kafirins are so
different in structure from the wheat gliadin and glutenin storage proteins
(Ciacci et al., 2007). Coeliac disease (CD), a syndrome characterized by
damage to the mucosa of the small intestine, is caused by ingestion of wheat
gluten and similar proteins (Catassi and Fasano, 2008). Therefore, sorghum
flour is an interesting alternative to gluten-containing cereals for the coeliac
market and because of its neutral flavour and the use of hybrids with a
white pericarp which are able to produce flour similar to wheat flour in
appearance and colour (Duodu et al., 2003).

8.2.3 Lipids
The total lipid content of sorghum ranges from 2.1 to 6.6 g per 100 g dry
weight, depending on the seed fraction and cultivar type. Moreover, these
factors influence the lipid composition and quantity.

The germ contains 80 % of the lipid in the sorghum kernel. Smaller
amounts of lipids are also present in the endosperm. The typical fatty acid
composition of sorghum lipids is similar to that of maize and mainly consists
of linoleic (49 %), oleic (31 %), and palmitic (14.3 %) acids (Hoseney et al.,
1981).

8.2.4 Minerals and vitamins
Sorghum is an important source of minerals and amongst them, P is the
most abundant (Kent and Evens, 1994) (Table 8.5). However, its

Table 8.5 Mineral and vitamin composition of sorghum

Minerals (mg/100 g dwb)a Vitamins (mg/g unless otherwise stated)

Major 30 Thiamin 0.46
Ca 52 Riboflavin 0.15
Cl 277 Niacin 4.84
K 148 Pyridoxine 0.59
Mg 11 Pantothenic acid 1.25
Na 305 Biotin 0.02
P 116 Folacin 0.02
S 200 Carotenes (mg/Kg) 29.0
Si
1.0 Vitamin E (mg/Kg) 12.0
Minor 7.0
Cu 2.6
Fe 3.0
Mn
Zn

adwb = dried weight basis.
Sources: Data adapted from Kent and Evens (1994), Gazzaz et al. (1989), Hulse et al. (1980).

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bioavailability is negatively related to the proportion which exists bound as
phytates. Minerals are located in the pericarp, aleurone layer and germ;
therefore, refined sorghum products lose part of these important nutrients,
as in all other refined cereal fractions.

Sorghum is an important source of fat-soluble and B-complex vitamins
(Waniska et al., 2004) (Table 8.5) except vitamin B12 (Gazzaz et al., 1989).
Amongst the B vitamins, concentrations of thiamine, riboflavin and niacin
in sorghum were comparable to those in maize. Some yellow-endosperm
sorghum varieties contain β-carotene which can be converted to vitamin A
by the human body (Dendy, 1994b). Detectable amounts of other fat-
soluble vitamins, namely D, E and K, have also been found in the sorghum
germ. Sorghum, in its typical form of consumption, is not a source of vitamin
C (Dendy, 1994b).

8.2.5 Tannins and phenolic acids
Tannins of sorghum are almost exclusively of the ‘condensed’ type, also
known as proanthocyanidins or procyanidins (Serna-Saldivar and Rooney,
1995) and are only present in cultivars with a pigmented testa (referred to
as brown sorghum but now classified as tannin sorghums). However, all
sorghums contain phenolic acids, which are located in the pericarp, testa,
aleurone layer and endosperm (Hahn et al., 1984). Tannins are mainly
polymerized products of flavan-3,4-diols (Fig. 8.4) (Gupta and Haslam,
1978; Gujer et al., 1986; Gu et al., 2002; Awika, 2003).

The tannin levels vary amongst sorghum genotypes and range from 10.0
to 68.0 mg/g (dry weight) (Jambunat and Mertz, 1973; Steadman et al., 2001;
Dykes and Rooney, 2006). They primarily reside in the pigmented testa,
which is only a portion of the outer covering, comprising approximately
5–6 % (dry weight) of the kernel. Tannins protect the grain against attack
by pests, such as birds, insects, moulds and bacteria, pre-harvest germination
and environmental effects (Waniska et al., 1989). The agronomic advantages
of the protective tannins are conversely accompanied by a nutritional
inconvenience and reduction in food quality. In fact, condensed tannins
bind to proteins, carbohydrates and minerals, thus reducing their digest-
ibility and decreasing the feed efficiency by 5–15 % (depending on the
livestock species and processing of the rations) (Waniska et al., 2004). To
reduce these negative effects, various processing mechanisms, such as
decortication, fermentation, germination (malting) and chemical treatment
(i.e. chloric acid, formaldehyde and alkali), are used (Beta et al., 2000).
Amongst them, malting effectively lowers (up to 43 %) the assayable levels
of sorghum tannins (Osuntogun et al., 1989). However, during malting,
tannins affect malt amylase activity, but alkaline or formaldehyde treat-
ments effectively counteract this phenomenon, thus allowing brewers to
avoid the associated problems (Beta et al., 2000).

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298 Cereal grains for the food and beverage industries

OH OH
OH OH

HO O HO O

OH OH n =1 - >10 OH OH
O OH O OH

OH OH
HO HO

OH OH OH
HO OH OH
Procyanidin B1 (5)
OH

O

OH OH
OH
Polyflavan-3-ol (3) OH

OH HO O OH
OH
O
HO O OH

O

OH OH
OH Catechin (4) Epicatechin gallate (6) OH

Fig. 8.4 The proanthocyanidins most commonly reported in sorghum: 3 and 4
(Gupta and Haslam, 1978; Gu et al., 2002); 5 (Gupta and Haslam, 1978); 6 (Awika,
2003). Reprinted with permission from ‘Phytochemistry’ 65, Sorghum phytochemi-
cals and their potential impact on human health, 1199–1221 (2004) (Elsevier

publishers).

The tannin sorghums are a potent source of antioxidants (Riedl and
Hagerman, 2001), which is mainly attributed to their chemical structure
containing many aromatic rings and hydroxyl groups, and additionally
tannins are not able to act as pro-oxidants (Hagerman et al., 1998).

The phenolic acids of sorghum are derivatives of benzoic or cinnamic
acid. As in other cereals grains, phenolic acids in sorghum are mainly con-
centrated in the pericarp and occur mostly in a bound form (esterified to
cell wall polymers).The most abundant phenolic acids identified in sorghum
include syringic, protocatechuic, caffeic, p-coumaric (70–230 μg/g dry weight)
(Hahn et al., 1983), ferulic (1400–2170 μg/g dry weight) (Hahn et al., 1984)
and sinapic (100–630 μg/g dry weight) (Hahn et al., 1984) acids (Waniska
et al., 1989). The phenolic acids are thought to play a role in plant defence
against pests and pathogens. Their content in sorghum correlates most
strongly with in vitro antioxidant activity and thus may contribute to health
benefits associated with consumption of whole-grain sorghum (Awika and

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Rooney, 2004). Their health-promoting properties, in particular their anti-
oxidant activity, their use as nutraceuticals and their applications in func-
tional foods, have been reviewed by Dykes and Rooney (2006).

8.3 Sorghum milling

The technology of milling sorghum grain into flour is not as well developed
relative to wheat (Taylor and Dewar, 2001), and in many countries sorghum
milling is still carried out by traditional methods (Taylor and Belton, 2002).
Generally, the first step of milling is decortication, a process aiming to
remove the bran layers (pericarp and germ), thus reducing tannin and
phytic acid contents. Decortication can be performed using either the attri-
tion or abrasion principle. Decortication by abrasive action can remove the
outer pericarp and seed coat layers of the grain, where the majority of the
tannins are located (Hahn and Rooney, 1986). However, this technique can
result in a low milling yield and high protein loss due to the softness of the
endosperm, a characteristic feature of some high-tannin sorghums (Reichert
et al., 1988). The decorticated material is then milled, gravity separated and
sieved to produce low-fat grits, meal and flour.

Nowadays, modern sorghum-milling processes involve roller mills (a
simple version of those used for wheat milling) with two or three pairs
of rollers in combination with a vibrating screen sieving device (Kebakile
et al., 2007), thus coupling decortication and particle size reduction. The
incorporation of the reduction rolls permits the production of fine sorghum
flour which is suitable for use in baking. In general, 5–20 % of the initial
weight is removed, depending on the degree of refinement desired (Rooney
and Waniska, 2000). Removal of the bran significantly influences the flour
composition. There is an increase in protein content but a strong reduction
in its quality. This is due to the removal of at least a part of the lysine-rich
germ which is the primary essential amino acid in sorghum (Taylor and
Schussler, 1986). Germ removal also substantially reduces the lipid (includ-
ing tocopherols), vitamin (especially those belong to the B group) and
mineral contents. However, mineral bioavailability may be improved when
the bran is removed since it is rich in antinutrient phytic acid which binds
and renders divalent minerals, such as zinc, iron and calcium, useless (Klop-
fenstein and Hoseney, 1995).

8.4 Applications in foods and beverages

Sorghum has considerable potential in food and beverage applications. As
it is gluten-free, it is suitable for coeliac sufferers. Sorghum is also a poten-
tially important source of nutraceuticals such as antioxidant phenolics
and cholesterol-lowering waxes. Whole-grain-type products, breads and

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300 Cereal grains for the food and beverage industries

pancakes, dumplings and couscous, porridge, gruels, cakes, cookies, pasta, a
parboiled rice-like product, snack foods, beers, non-alcoholic fermented
beverages and even distilled spirits have been successfully produced from
sorghum (Taylor and Belton, 2002; Schober et al., 2006; Taylor et al., 2006).

8.4.1 Bakery products from sorghum
The most popular unfermented flat breads from sorghum are roti in India
and tortillas in Central America. To make roti, a kind of dry pancake, finely
milled sorghum flour is mixed with warm water and kneaded together to
make cohesive dough, which is shaped into a circular disc 12–25 cm in
diameter and 1.3–3.0 mm thick, and subsequently baked in a hot griddle.

Although tortillas are generally made from maize, sorghum has been
used in several Central American countries. Sorghum can be partially or
totally substituted for yellow maize in tortilla production (Bedolla et al.,
1983) when properly processed (i.e. decorticated to remove outer bran
layers and cooked and steeped for a shorter time than maize), thereby
producing tortillas with acceptable colour, flavour and texture (Choto et al.,
1985). For tortilla production, whole sorghum is lime-cooked, steeped over-
night, washed, stone ground into masa, shaped into thin circles and baked
on a hot griddle (Waniska et al., 2004).

Serna-Saldivar et al. (1988) reported that lime treatment and cooking
do not affect the total protein or amino acid contents of sorghum grains,
but reduce the digestibility of the essential amino acids. Cooking reduces
the digestibility of some prolamins, such as β- and γ-kafirins, while the
use of reducing agents increases the digestibility of these proteins (Oria
et al., 1995). Further details on sorghum tortillas are given by Murty and
Kumar (1995), Rooney and Serna-Saldivar (2000) and Rooney and Waniska
(2000).

In North Africa, sorghum flour is widely used for the production of
popular fermented breads such as injera (Ethiopia) and kisra (Sudan). For
the production of injera, sorghum flour is mixed with water and a yeast
starter from a previous batch of injera. After fermentation for 24–48 h, the
batter is poured onto a greased pan for baking. The resulting product is
flexible, and its surface has essentially evenly spaced gas holes, that make
up a honeycomb-like structure which has been formed through gas produc-
tion during the preceding fermentation and baking. The bottom surface of
injera is smooth and shiny. A good injera is soft, fluffy and able to be rolled
without cracking. It should retain these textural properties after two to
three days of storage, which is traditionally in a straw basket. A slight sour-
ness is a characteristic taste of injera.

Kisra constitutes the staple diet of the Sudanese population. It is pre-
pared from the fermented dough of sorghum grains. Sorghum flour is
mixed with water in a ratio of about 1 :2 (w/v), usually a starter is added
by a back-slopping using mother dough from a previous fermentation

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incorporated at a level of about 10 %. Fermentation is completed in about
12–19 h by which time the pH drops from about 6.0 to less than 4.0 (Asmahan
and Muna, 2009). The fermented dough is then baked into thin sheets and
is eaten with certain types of stew prepared from vegetables and meat
(Mahgoub et al., 1999).

Perten et al. (1983) reported that the quality parameters (volume, texture
and colour) of sorghum bread were significantly inferior to those observed
for wheat bread, mainly due to the inability of sorghum to produce the
elastic dough needed to obtain a large bread volume. The same authors
suggest that the incorporation of 30 % sorghum flour to wheat flour can
give a larger bread volume than that made from 100 % wheat flour of poor
quality. Bread made with 30 % sorghum flour and 70 % wheat flour, of a
72 % extraction rate, was evaluated as being ‘good to excellent’ in accept-
ability tests.

Schober et al. (2005) investigated the bread-making quality of 10 sorghum
flours when incorporated in a recipe containing sorghum flour (70), corn
starch (30), water (105), salt (1.75), sugar (1) and dried yeast (2). They found
how starch damage, influenced by kernel hardness, was recognized as a key
element influencing the hardness and the mean cell area of the crumb.
Moreover, they observed that the increasing water levels (from 100 to
115 % flour weight basis [fwb]) increased loaf specific volume, while increas-
ing xanthan gum levels (form 0.3 to 1.2 % fwb) decreased the volume. When
skim milk powder level was increased (from 1.2 to 4.8 % fwb), loaf height
decreased.

It is particularly clear that without the benefit of wheat’s gluten proteins
and the gas-holding properties they provide, breads made solely from
sorghum required a different bread-making technology. The number of
studies addressing wheat-free sorghum bread is limited. To compensate
for the gluten absences, different additives have been employed, such
as gums (Carson and Sun, 2000; Elkhalifa et al., 2007), hydrocolloids
(Onyango et al., 2009), enzymes (Onyango et al., 2010) and starches
(Onyango et al., 2009). The majority of these studies indicated that more
than one combination of these additives and water could yield high baking
volumes.

Sorghum flours have also been used to produce biscuits, granolas and
snack foods such as crisps, chips and sham date. Badi and Hoseney (1976)
studied the eating quality of cookies made from sorghum grains. Cookies
made from sorghum flour were tough, fragile, gritty and mealy. The fragility
problem is due to the absence of gluten, which normally provides dough
cohesiveness, while the gritty texture can most likely be attributed to hard,
sharp-edged endosperm particles or bran. After baking, it might also be a
consequence of the high gelatinization temperature of sorghum starch,
leaving some granules ungelatinized.

The biscuit fragility can be reduced by adding wheat lipids, such as phos-
phatidyl ethanolamine, digalactosyl diglycerides and phosphatidyl choline,

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302 Cereal grains for the food and beverage industries

that are absent in sorghum, or using emulsifiers such as lecithin and sucrose
fatty esters (Badi and Hoseney, 1976). Adding wheat flour lipids to defatted
sorghum flour improved top surface texture and spread of the cookies,
although they were still clearly inferior in quality to cookies made from soft
wheat (Badi and Hoseney, 1976). Grittiness in sorghum cookies can be
significantly reduced by increasing the pH of the dough or extruding part
of the cookie flour (Taylor and Belton, 2002).

Leon-Chapa (1999) found that up to 50 % sorghum flour could be sub-
stituted for wheat flour in cookies without affecting the acceptability. The
cookies made with 100 % sorghum flour were fragile and crumbly. More-
over, higher amounts of damaged starch in sorghum flour significantly
improved the quality of cookies (Leon-Chapa, 1999).

8.4.2 Porridge
Porridges are popular sorghum foods. Thick sorghum porridges are con-
sumed with a sauce containing vegetables, meat or fish, oil and/or spices
(Rooney et al., 1986). Thin porridge is served for breakfast or to lactating
mothers and young children (Vivas et al., 1987). Ogi is a traditional porridge
in Nigeria and is manufactured by wet-milling sorghum, maize or millet. It
is prepared by steeping clean whole sorghum grains in water at room tem-
perature for 48–72 h. The fermented grain is washed with clean water and
then crushed into a water paste or slurry which is subsequently sieved to
remove the bran. The flowthrough is allowed to ferment for 24–48 h. Excess
water is removed and the resulting slurry is cooked in milk or water to make
thin or thick porridge (Banigo and Muller, 1972).

Akingbala et al. (1981) showed that non-waxy white sorghums gave ogi
the highest ratings in terms of colour, taste, texture, aroma and consistency.
In contrast, waxy sorghums produced ogi with a poor and undesirable con-
sistency. Moreover, the brown high-tannin sorghums produced ogi with
undesirable brownish-red colour, poor consistency and texture, and low in
vitro starch and protein digestibility.

8.4.3 Couscous
Couscous is prepared by mixing sorghum flour with water, agglomerating
the flour–water mixture into small granules, steaming and drying. Abouba-
car and Hamaker (1999) demonstrated that hard grain (with corneous
endosperm) produced flours containing a high proportion of coarse parti-
cles with low ash and high damaged starch contents, yielding a higher
proportion of desirable sorghum couscous granules. Additionally, they
observed that cooked couscous hardness correlated positively with the
apparent amylose content of flour and correlated negatively with flour peak
time (Aboubacar and Hamaker, 1999). Couscous is consumed with milk or

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buttermilk for breakfast or is served with a sauce containing fish for meat
for lunch or dinner (Aboubacar and Hamaker, 1999).

8.4.4 Sorghum pasta
It has been found that good-quality pasta that can retain satisfactory
cooking quality and colour may be produced replacing 30 % of wheat flour
with sorghum flour. Pre-gelatinization of 25 % of sorghum flour, before
blending it with the remaining 75 %, gave good cooking characteristics, but
the colour was unacceptable to the consumers (reviewed by Faure, 1992).
An interesting option is the use of heat treatment during drying. Heat treat-
ment of the pasta at 90 ˚C before the drying step has been found to improve
cohesiveness and reducing cooking losses (Faure, 1992). Liu et al. (2012)
found that, through control of sorghum grain and flour quality characteris-
tics, it is possible to manufacture a Chinese egg noodle with good physical
attributes. In particular, flour with fine particle size and high starch damage
increased the water uptake and resulted in noodles with high firmness and
high tensile strength and a cooking loss below 10 %.

8.4.5 Sorghum-based beverages
In Africa, there are many traditional native sorghum-based opaque beers.
They are named according to the language of the local tribes and so in the
countries of modern Africa it is often possible to find more than one name
for essentially the same beverage, such as ioala (South Sotho – Lesotho),
bjalwa (Pedi – South Africa), oruramba (Uganda). These sorghum-based
beers are made from malted sorghum and unmalted maize (Odunfa, 1985)
and differ considerably from conventional clear lager-type beers. They are
opaque and pinkish-brown in colour due to the presence of the yeast
and the large quantities of suspended particles of starch and other grain
material (dextrins which are not digested during mashing and fermenta-
tion) (Glennie and Wight, 1986). The gelatinized starch gives the beers a
viscous consistency resembling a thin gruel with a sour, yoghurt-like taste
(Haggblade and Holzapfel, 2004). The main steps involved in the produc-
tion of this opaque beer are malting, converting the cooked sorghum into
fermentable sugars, souring the mash and finally fermenting the sugars into
alcohol. The success of brewing is critically dependent on the quality of the
malt, particularly its enzyme composition (proteases and maltase). Unlike
European-type beer, the sorghum opaque beers are not hopped, are typi-
cally unpasteurized and are consumed while actively fermenting (Taylor
and Belton, 2002; Waniska et al., 2004). Generally, the two main quality
parameters for opaque beers are the sourness of the beer, due to lactic acid
fermentation, and, secondly, the less important factor of alcohol content (up
to approximately 3 wt%).

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304 Cereal grains for the food and beverage industries

Malting and brewing with sorghum to produce lager and stout, often
referred as clear beer, has been conducted on a large, commercial scale
since the late 1980s, notably in Nigeria (Ilori et al., 1996) where the import
of barley and other cereals is forbidden to save foreign exchange (Taylor
and Belton, 2002). Since unmalted sorghum contains very low levels of
enzymes (Taylor and Robbins, 1993), commercial enzymes, including
α-amylases, maltogenic amylases, proteases and hemicellulases, replace the
malt enzymes (Bajomo and Young, 1994). In this regard, Goode et al. (2002)
found that the addition of malted barley in small proportions to unmalted
sorghum mashes together with commercial enzymes (Goode et al., 2003)
improve the potential for brewing a high-quality lager beer from unmalted
sorghum. Unlike barley malt, sorghum starch is characterized by a high
gelatinization temperature which is in excess of malt amylase working
temperatures. To overcome this problem, a decoction-type mashing process
facilitates the complete gelatinization of the sorghum malt starch, whilst
maintaining maximum malt enzymatic activity (Taylor and Belton, 2002).

Pilot-scale (1000 L) brews were carried out by Goode and Arendt (2003)
with a grist comprising unmalted sorghum (50 % of total wet weight of
grain) (South African variety) and malted barley (50 % of total wet weight
of grain) grist. A control brew containing 100 % malted barley was also
carried out. The sorghum beers matched quite closely with the control beer
with regard to colour, pH and colloidal stability, and sensory attributes
(aroma, mouth feel, after-taste and clarity). However, foam stability defi-
ciencies were apparent with the sorghum beer.

Since sorghum is a huskless grain, the filtration step, necessary to produce
clear wort, is carried out using mash filters (Little, 1994). The sorghum-
brewed clear beers are characterized by a lesser content of volatile com-
pounds, especially ethyl acetate and diacetyl, than conventional beers
(Little, 1994). Nigerian brewers produce clear beers characterized by sweet-
ish and generally slightly sour tasting, fruity aroma and containing 1–5 %
(v/v) alcohol (Rooney and Serna-Saldivar, 2000).

8.5 Conclusions

Sorghum is the fifth most important cereal crop after wheat, maize, rice and
barley and, from a growth and survival perspective, out performs other
cereals under various environmental stresses, in particular in the warmer
temperatures and tropical regions of the world.

Sorghum is widely utilized around the world as feed and food. It is also
a potentially important source of nutraceuticals, such as antioxidant phe-
nolics and cholesterol-lowering waxes. The nutritive value of sorghum is
lower than that of other cereals because of a low content of some essential
amino acids, especially lysine, tryptophan and threonine and, additionally,
due to the presence of condensed tannins and phytic acid. However, its

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nutritional value can be significantly improved through fermentation and
germination processes.

8.6 Future trends

Sorghum has extensive potential for wider use due to its agronomic char-
acteristics and organoleptic/nutritive properties. However, resolution of
some serious technical problems has to precede any widespread utilization
of sorghum as an industrially produced food. In bread-making, further
research could focus on attempts to create a visco-elastic protein network
in order to improve the texture and shelf-life of the gluten-wheat-free
bakery products. Regarding sorghum brewing, sorghum malting without
exogenous enzymes seems to require genetic modification of the grain to
reduce starch gelatinization temperatures and increase malt β-amylase
activity. Alternatively, precooking a portion of the grain in advance of
malting could partially alleviate this problem.

Due to low protein digestibility, and particularly its reduction during the
cooking process, sorghum can be used to reduce the caloric intake for
Western populations (over-consumption of refined foods) where protein
deficiency is not an issue. Additionally, the use of sorghum for the produc-
tion of nutraceutical ingredients, functional foods containing antioxidant
polyphenols, incorporation of porridge/gruel as a substrate for probiotic
beverages, and as a gluten-free substitute for coeliac sufferers all potentially
point in the direction of developing new interesting industrially viable niche
markets for sorghum. Lastly, the development of sorghum-based conve-
nience foods will increase the demand for this promising crop.

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9

Millet

DOI: 10.1533/9780857098924.312

Abstract: The millets are various grass crops that are extremely important in
the semi-arid and sub-humid zones as staple crops for animals and humans.
According to FAO data, the productions of millets increased slightly from 24.8
million tonnes in the 1980s to 28–34.9 million tonnes in the period 2001–2008.
Proso millet, also named common millet, hog millet, broom corn, yellow hog,
hershey and white millet, is one of the oldest crops known to mankind. Proso
millet contains a high level of methionine and cystine and therefore is
nutritionally equivalent or superior to maize, rice, wheat, rice and sorghum where
these vital amino acids are deficient or low. As proso millet is not closely related
to wheat, it represents an appropriate food for people with coeliac disease or
other forms of allergy or intolerance to wheat. Several foods are prepared from
proso millet, and then differ from country to country. Primary uses for proso
millet include various forms of porridge, steamed food products, cakes, fermented
and unfermented breads, snacks, weaning foods and alcoholic and non-alcoholic
beverages. With the world faced with climatic alterations, proso millet with its
distinctive ability to grow in hot dry areas with poor soils should become a far
more globally important food grain.

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

9.1 Introduction

The millets are various grass crops that are extremely important in the
semi-arid and sub-humid zones as staple crops for animals and humans.
Considering the fact that the average global surface temperature is pro-
jected to increase by 1.4–5.8 °C from 1990–2100 due to the emission of
greenhouse gases in the atmosphere (World Organisation for Animal
Health, 2006), millets, and in particular proso millet (Panicum miliaceum L.),
represent an interesting crop since they need less water to grow than any
other cereal (Winch, 2006). Proso millet, also named common millet, hog
millet, broom corn, yellow hog, hershey and white millet (Baltensperger,
1996), is one of the oldest crops known to mankind. Scholars have suggested
that it was cultivated during the Neolithic period (8000–2000 BC) in China

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Millet 313

(Hoffmann-Bahnsen and Plessow, 2003) and that Chinese farmers cultivated
both a waxy (amylose-free starch) and a regular species of proso millet
during the Second Chinese Dynasty (Kolb, 1992). Discoveries made in the
middle and eastern parts of Europe point to the cultivation of proso millet
in this area during the Linear Band Pottery culture (about 5000 BC)
(Knörzer, 1999). Due to the extension of the acreages used for growing
potatoes, proso millet became increasingly less important in Europe and had
almost disappeared as a field crop in the western part of Europe by the
beginning of the 20th century (Hanelt, 1981). Proso millet continues to play
an important role in northwest China and is also commonly cultivated in
Kazakhstan, Eastern Europe and the USA, among other countries. It is
the third most important millet, after pearl millet (Pennisetum glaucum)
and foxtail millet (Setaria italica). According to FAO (Food and Agriculture
Organization of the United Nations), millet production (as a whole includ-
ing pearl millet, foxtail millet, proso millet, finger millet, teff, fonio millet
and others) ranks fifth in world production statistics, following corn, wheat,
barley and sorghum. In the last 11 years, millet production increased
slightly from 27.6 million tonnes in 2000 to 31.6 million tonnes in 2010,
with a peak in 2008, where millet production reached 34.9 million tonnes
(FAO/UN, 2012) (Table 9.1). Suggested food applications for dehulled proso
millet include as a puffed or cooked breakfast cereal or as a replacement
for wheat flour in certain baked products and other household recipes
(Hinze, 1972).

9.1.1 Production, price, yield and area
Proso millet is grown in temperate climates. It is widely cultivated in
the Russian Federation, the Ukraine, Kazakhstan, USA, Argentina and
Australia (Léder, 2004) and also plays an important role in the central and
southern states of India and Eastern Europe. A sizeable proportion (about
100 000 tonnes) of proso millet is exported by the USA, Argentina and
Australia to other developed countries. India exports approximately 60 000
tonnes of pearl millet and in recent years, China has started to export foxtail
millet. In 2010, their harvested areas occupied 37.8 million hectares, with a
production yield around 0.9 tonnes/ha (FAO/UN, 2012). The major millet
importers in 2010 were Belgium, Germany and the Netherlands with 26 700,
23 100 and 16 000 tonnes, respectively (FAO/UN, 2012). Exact statistics on
production and trading are hard to come by since proso millet is mostly
grouped with other millets as ‘other cereals’ in official data. Prices of inter-
nationally traded proso millet are highly volatile and depend on supply and
demand. Over a five-year period (1993–1998), proso millet produced in the
USA sold for between US$88 and US$550 per ton. The price in March 2003,
for example, was very high (US$690) as a result of severe drought in pro-
duction areas in the USA (Burgener et al., 2002). In general, millet prices
are higher than those of other cereals.

© Woodhead Publishing Limited, 2013

Table 9.1 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: FAO/UN (2012).

Millet 315

9.1.2 Phytology, classification and cultivation
Proso millet (Panicum miliaceum L.) belongs to the order Poales, the family
Gramineae, the sub-family Panicoideae and the tribe Paniceae, which
includes 80 genera. It is an annual cereal grain that produces bright green
leaves and small seeds (Kemper Center for Home Gardening, 2005; Skinner,
2005).

It is considered a short-day plant, reaching 30–100 cm in height with
few tillers and an adventitious root system. Proso millet is considered to be
a self-pollinated crop, but natural cross-pollination may exceed 10 %
(Baltensperger, 2002). The seeds are generally oval in shape and, at about
3 mm long and 2 mm wide, are normally smaller than those of pearl millet
(P. glaucum) (Baltensperger, 2002). Proso millet is well adapted to many soil
and climatic conditions. Being a short-season crop (60–75 days) with a low
water requirement, it grows further north (up to 54°N latitude) than the
other millets and also adapts well to plateau conditions and high elevations
(Matz, 1986). Proso millet can be cultivated at altitudes of up to 3500 m
(Baltensperger, 1996). For optimal growth, the annual average of precipita-
tion should be less than 600 mm and the average daytime temperature
during vegetation should be above 17 °C. Furthermore, the plant requires
only small amounts of nitrogen fertilizer and it is quite resistant to plant
diseases (Humphrys, 2005), so crop rotation problems are not normally an
issue.

Proso millet is classified into five sub-species depending on the type of
panicle (patetissimum, effusum, contractum, ovatum and compactum)
(Zarnkow et al., 2010). Within these sub-species, proso millet is further
divided into varieties, whose distinctive characteristics are the colour of the
grain, the type of the husk and the appearance of the anthocyanin dye in
the peduncle-spikes and husks (Lysov, 1968). The varieties can also differ
in maturation time and seed size. Seed colours include creamy white, yellow,
orange, red, black or brown (Baltensperger, 2002; Kemper Center for Home
Gardening, 2005). Millet grains are illustrated in Fig. 9.1.

9.1.3 Structure of the proso millet grain
As a member of the order Poales proso millet is a monocotyledonic plant,
whose identifying characteristic is its single seed leaf. The husks of proso
millet have a smooth surface (Lorenz, 1977), and the basic kernel struc-
ture is similar to that of other millets. The principal anatomic components
are the pericarp, the seed coat (or testa), the aleurone layer, the germ (or
embryo) and the endosperm (Figs 9.2 and 9.3). The thin pericarp is loosely
attached to the endosperm. In these so-called utricle-type kernels, the
pericarp easily breaks away, leaving the seed coat to protect the inner
endosperm. The testa simply consists of one layer, whose thickness is
between 0.2 and 0.4 μm. The aleurone layer completely surrounds the
endosperm and germ. The aleurone cells are 25–50 μm in length with

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316 Cereal grains for the food and beverage industries

Fig. 9.1 Millet grains.

Style

Pericarp
Seedcoat

Aleurone layer
Corneous
Peripheral
endosperm

Floury endosperm

Scutellar epithelium

Scutellum

Embryonic
axis

Hilum
Fig. 9.2 Longitudinal section of a pearl millet grain.

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Millet 317

Pe

AI P
Sc T

F

G

L ×50 2 mm

Fig. 9.3 Structure of a longitudinally-cut proso millet kernel using SEM Hitachi
TM-1000, magnification = ×50. Al = aleuronelayer, F = floury endosperm, G = germ,
P = pericarp, Pe = peripheral (corneus or streaky) endosperm, Sc = scutellum,
T = testa (seed-coat). Reprinted from Zarnkow et al., 2007, with permission from

the Journal of the Institute of Brewing.

protein bodies and distinctive spherosomes (Serna-Saldivar and Rooney,
1995).

In comparison to other grains, proso millet has a small embryo and hence
the endosperm to germ ratio is between 12 :1 and 11 :1 (Serna-Saldivar and
Rooney, 1995).The scutellum consists of irregularly shaped cells and appears
in the form of two wing-like expansions (Serna-Saldivar and Rooney, 1995).
Lorenz (1977) described angular starch granules in the streaky endosperm
and spherical granules in the floury area. Kumari and Thayumanavan (1998)
found that the starch granules had a mainly bimodal distribution in terms of
shape and size. They observed small spherical granules and large polygonal
granules, together with the occasional large spherical granule (Fig. 9.4).
Overall, the size of the starch granules ranges from 1.3 to 13.5 μm (Lorenz,
1977; Yanez et al., 1991; Kumari and Thayumanavan, 1998) and the mean
diameters vary from approximately 4–5 μm (Yanez et al., 1991). Scanning

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