Biomedical Engineering Reference
In-Depth Information
content, which promotes greater animal weight gain per unit of feed. Nevertheless, corn
varieties with oil content higher than 6% tend to have lower crop yields.
In 2007, about 98% of the world corn production was consumed as food or feed (USDA-
FAS, 2008). The majority of the corn grown in the United States is used as feed. Nearly 43%
of the 2009 US corn production was used as feed or left as residue on the field (NCGA,
2010). The same year biofuel, particularly the ethanol production industry, utilized almost
32% of the corn grown in United States. The shares of food/cereal and high fructose corn
syrup production in corn consumption were relatively low, 5 and 12 million tonnes,
respectively. The high fructose corn syrup production industry takes up about 3-4% of total
United States corn production.
Besides its food and feed use, corn has numerous other industrial applications. According
to the US National Corn Growers Association, there are more than 4200 different uses for
corn products (NCGA, 2010). Although zein, a major storage protein in corn, is not directly
used for human consumption it has many potential industrial applications in fiber, adhesive,
coating, ceramic, ink, cosmetic, textile, chewing gum and biodegradable plastics production
(Shukla and Cheryan, 2001). Biofuels, starch and high value products such as recombinant
pharmaceutical proteins and specialty chemicals are some of the economically important
corn-based products (Naqvi et al ., 2011 ).
A significant fraction of United States corn is used to produce ethanol. Corn is converted
into ethanol primarily by two processes: wet milling and dry grinding. In wet milling, the
corn kernel is fractionated into germ, fiber, and starch resulting in several co-products. The
starch portion of the corn kernel is converted to ethanol, while the protein, fiber and oil are
passed through to the by-products. Only one co-product, distillers' dried grains with solubles
(DDGS), is produced when dry milled corn is used for ethanol production. Every bushel of
corn (approximately 25 kg) processed for sweeteners, oil, or ethanol generates nearly 7 kg of
protein and fiber-rich residues (Leathers, 2003). Currently these by-products are used in low
value applications. It has been suggested that ethanol production industry by-products have
the potential to be used as inexpensive fermentation media for production of polysaccharides
and carotenoids by yeasts or yeast-like fungi (Leathers, 2003). The potential of DDGS for
value-added product development has also been explored. Utilization of DDGS as a substrate
for biobutanol production by various clostridia species is an area that is drawing attention
(Ezeji and Blaschek, 2008 ).
Today corn is the leading platform to synthesize high value molecules, including
pharmaceuticals, through biotechnology. Corn has a number of advantages over other plants
for molecular pharming in crops. These advantages include its GRAS (Generally Regarded
As Safe) status, well characterized genetic properties, responsiveness to in vitro manipulation
and gene transfer, well established agricultural infrastructure and efficient biomass
production (Ramessar et al ., 2008). Initially new traits for herbicide tolerance and pest or
disease resistance were introduced into corn. Recent research on metabolic pathways that
produce primary and secondary metabolites, specifically the compounds that are beneficial
for human health and nutrition, has led to the introduction of novel traits in to corn. In a
recent article utilization of advanced biotechnology tools to produce a broad range of high
value molecules in corn was reviewed (Naqvi et al ., 2011 ). Some of the compounds
successfully produced in transgenic corn include amino acids (Galili and Höfgen, 2002),
very long chain polyunsaturated fatty acids (Napier et al ., 2006 ), vitamins (Giuliano et al .,
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