Maize Starch for Industrial Applications - Industrial Crops: Breeding for BioEnergy and Bioproducts - page 177

traits have been available in regular field corn since 1996 and have simplified
production, decreased costs, and increased yield [ 31 - 33 ]. The potential to capture
similar gains has motivated the promotion of genetically modified waxy hybrids.
Amylose specialty hybrids, in contrast to waxy, have a yield reduction of 20-
25 % in comparison to dent isogenic materials [ 26 ]. Amylose starch granules are
smaller and irregularly formed, suggesting that the rate of starch polymerization or
the configuration of the granular crystallized lamella is disrupted [ 34 ]. The enzyme
complex formed in high-amylose corn is distinct and does not follow the same
activity cycle as compared to the dent wild type [ 35 , 36 ]. Effectively the plant is
unable to assemble the most efficient protein configuration and defaults to a less
efficient aggregate [ 36 ].
As with waxy, slower grain dry down and higher grain moisture later in the
season may contribute to yield loses and disease susceptibility. High-amylose
hybrids have been commercialized on a much smaller scale than waxy hybrids,
and fewer breeding programs pursue their research and development. The addi-
tional requirement of amylose modifier genes also contributes to limit development
of high-amylose donor material, and linkage drag effects impact yield to greater
degree than in waxy conversions.
Transgenic conversions to control expression of the amylose-extender gene are a
strategy that has been pursued not only for corn but also for several other agronomic
crops including rice, wheat, barley, potato, and sweet potato [ 37 - 42 ]. Transgenic
conversions provide valuable insight into starch functionality but have not been
widely used for any commercial applications.
Not all wet-mill facilities accept genetically modified waxy grain, and especially
those that serve food industry will often require grain channeling, identity preser-
vation, and handling documentation.
Starch Pathway Genetics
In high-moisture food applications such as sauces, spreads, fillings, and soups,
starches can affect and improve sensory aspects and confer creaminess, flowability,
and smoothness. In lower moisture foods like bakery, snacks, cookies, crackers, and
cereals, starches contribute to products perceived softness, crispness, stickiness, or
crunch.
The impact of native starch on food functionality is the result of several factors
including amylopectin and amylose content, amylopectin chain length and
branching properties, and starch interactions with lipids and proteins. Because of
the very specific nature of taste and food perception, small and subtle changes in the
starch can greatly impact the food experience.
With industrial use, the starch is often required to perform as a permanent
application with performance characteristics that must be maintained for a much
longer time frame. Chemical modification can be applied at a higher rate and
produce starches that are much more persistent. Industrial starches also do not