Traditional and Emerging Feedstocks for Food and Industrial Bioproduct Manufacturing - Food and Industrial Bioproducts and Bioprocessing - page 3

Table 1.1 Wheat, corn, sorghum and barley production in 2008 (million metric tons).

Wheat Corn Sorghum Barley

World 683.4 World 826.3 World 66.8 World 155.1

China 112.5 USA 307.1 USA 12.0 Russian

Federation

23.2

India 78.6 China 166.0 Nigeria 9.3 Ukraine 12.6

USA 68.0 Brazil 58.9 India 7.9 France 12.2

Russian
Federation 63.8 Mexico 24.3 Sudan 3.9 Germany 12.0

Classification of wheat for commercial purposes is based not on variety but on grain
properties such as softness/hardness, winter/spring growth habit, red/white bran and protein
content. Hard wheat has a hard kernel and produces high protein content flour suitable for
making bread and noodles. Soft wheat has lower protein content than hard wheat and is
mainly used for making cakes, biscuits and pastries. Winter wheat is planted in late summer
or fall and takes the advantage of fall moisture for germination. It is grown in regions where
soil does not completely freeze and kill the crop. As the name implies, spring wheat is sown
in spring and harvested in late summer. Yields for winter wheat tend to be higher than that
for spring wheat due to the risks associated with summer harvest (Pomeranz, 1988). Color,
white or red, refers to the color of the outer layers of grain. Depending on milling extraction
rate (bran removal rate), the color of the wheat flour can be quite dark, affecting the
appearance of the final product. Major wheat exporting countries have their own wheat
grading standards that are based on test weight, protein content, moisture, foreign material
content and so on (Bushuk and Rasper, 1994). The US Grain Standards Act is enforced by
inspectors under the supervision of the US Department of Agriculture (USDA, 2006).
Although wheat straw production yield depends on variety and agronomic and climatic
factors, in general 1.3 kg of straw per kg of grain is produced for the most common varieties
(Montane et al ., 1998). It is estimated that over 90 million metric tons (tonnes) of wheat
straw is produced annually in the United States. Considering that world wheat production
was about 683 tonnes in 2008 (Table 1.1), global wheat straw production would be
888 tonnes in the same year. About 500 kg of straw per acre needs to be left on the soil
surface during wheat harvest for erosion control of steeply sloped ground (Mckean and
Jacobs, 1997). It is apparent from these numbers that a significant amount of wheat straw is
available for value-added product development.

1.2.1.2 Chemical composition

Chemical composition of wheat fractions varies significantly by variety, agronomic and
climatic conditions and separation techniques used. Grain consists of 40-50% of the biomass
produced by the crop. Wheat grain structure is very complex and composed of many layers
(Godon, 1994). Broadly speaking wheat grain consists of endosperm, bran and germ, which
account for 81-84%, 14-16% and 2-3% of the grain, respectively (Atwell, 2001). Whole
wheat grain is generally processed by dry milling to obtain flour. Various forms of bran, germ
and the “clean-out” of the screen room represent almost 25% of the original wheat grain.
Carbohydrates make up about 60-80% of the dry grain weight. Starch is the main carbohydrate
found in endosperm or flour. Other carbohydrates present in wheat include free sugars,
glucofructans, cellulose and hemicellulose. Arabinose and xylose are the major free sugars.