Biomedical Engineering Reference
In-Depth Information
2008 ; Zhu et al ., 2008 ; Chen et al ., 2006 ; Ishikawa et al ., 2006 ) and minerals (Drakakaki
et al ., 2005). The emerging regulations that govern how transgenic corn plants and their
products are grown, used and traded were also discussed by Naqvi and co-workers (2011).
Utilization of corn stover for bioproducts has advantages over alternative crops that are
being examined as feedstock, because corn stover is already produced with grain and does
not require dedicated land. The challenge is to determine the sustainable levels of stover that
can be collected without adversely affecting ecosystems. Corn fiber is a by-product of the
wet-milling process that separates fiber, gluten and germ from starch. Stillage residues from
starch fermentation are folded into the corn fiber to produce corn gluten feed and sold as
low-value cattle feed. New co-products from corn fiber and gluten feed could also add value
to the corn processing industry. For example, it has been shown that corn fiber is a rich
source of oryzanol (ferulic acid esters of phytosterols), which has cholesterol lowering
properties (Jain et al ., 2008). Both corn fiber oil and gum have potential for functional food
applications (Yadav et al ., 2007 ).
1.2.3 Barley
Barley is among the four largest cereal crops (with wheat, maize and rice) grown in the
world (Newman and Newman, 2008). In 2008 global barley production was about 155.1
million tonnes (FAO, 2010). The top barley growing countries are the Russian Federation,
Ukraine, France and Germany. The United States was ranked as the ninth highest barley
grower in the world with 5.3 million tonnes of production in 2008.
Barley is a grass that belongs to the Poaceae family, Triticeae tribe and genus Hordeum
(Newman and Newman, 2008). One of the most important mutations associated with the
domestication of wild barley to cultivated barley was non-brittle rachis formation, which
resulted in efficient harvest without loss of grains (Pourkheirandish and Komatsuda, 2007).
Genetic variation in starch structure and composition determine the end uses of barley.
Traditionally, barley breeders focused on the improvements that benefit malting and the
brewing industries rather than the feed market because malting barley receives premium
price (Ullrich and Eslick, 1978). Recently, feed quality of barley has been receiving attention
from the breeders, partly because barley is becoming a very important feed crop due to
the increasing industrial uses and uncertainty in the availability of corn as feed (Rudi
et al ., 2006 ).
The first transgenic barley plants were developed in 1994 (Jähne et al ., 1994 ). Early
barley transformation studies aimed at improved grain quality for feed and beverages
(Jensen et al ., 1996 ; Horvath et al ., 2000) or disease resistance (McGarth et al ., 1997 ;
Leckband and Lörz, 1998). These studies have demonstrated that functional recombinant
proteins such as enzymes can also be produced in transgenic barley, specifically in grain.
Chemical Composition
Barley is classified in several ways depending on agronomic properties, chemical
composition and end use. The most common barley types are: spring and winter, two- and
six-row, hulled and hulless, malting and feed, normal, waxy and high amylose starch, high
lysine, high
-glucan, and proanthocyanidin-free barley (Baik and Ullrich, 2008). The
chemical composition of barley grain varies significantly with genotype, agronomic
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