Genetically Improved Crops - The Oxford Topic of Food, Politics, and Society - page 85

have demonstrated beneficial effects for human and animal health. Many, however,
have the opposite effect. For example, phytate, a plant phosphate storage compound,
is considered an antinutrient as it strongly chelates iron, calcium, zinc, and other diva-
lent mineral ions, making them unavailable for uptake. Nonruminant animals generally
lack the phytase enzyme needed for digestion of phytate. Poultry and swine produc-
ers add processed phosphate to their feed rations to counter this. Excess phosphate is
excreted into the environment resulting in water pollution. When low-phytate soybean
meal is utilized along with low-phytate maize for animal feeds, the phosphate excre-
tion in swine and poultry manure is halved. A number of groups have added heat- and
acid-stable phytase from Aspergillus fumigatus inter alia to make the phosphate and lib-
erated ions bioavailable in several crops (Potrykus 1999). To promote the reabsorption
of iron, a gene for a metallothionein-like protein has also been engineered. Low-phytate
maize was commercialized in the United States in 1999 (Wehrspann 1998).
In November 2009, the Chinese company Origin Agritech announced the final
approval of the world's first genetically modified phytase-expressing maize (Han 2009).
Research indicates that the protein in low-phytate soybeans is also slightly more digest-
ible than the protein in traditional soybeans. In a poultry feeding trial, better results
were obtained using transgenic plant material than with the commercially produced
phytase supplement (Keshavarz, 2003). Poultry grew well on the engineered alfalfa diet
without any inorganic phosphorus supplement, which shows that plants can be tailored
to increase the bioavailability of this essential mineral. A Danish group achieved a simi-
lar effect, where temperature-tolerant phytase resisted boiling (Brinch-Pedersen 2006).
As noted previously, JR Simplot has created one of the first output products to be sub-
mitted for non-regulated status, a potato with three specific modification for quality
improvement.
The three modified traits are important from a commercial perspective as they greatly
improve the quality of the potato, making it more appealing to both producers and
consumers. The first of those traits, reduced black spot from bruising and browning, is
achieved through RNAi suppression of polyphenol oxidase (PPO), effectively limiting
oxidation by silencing the endogenous PPO gene. Not only is this more appealing for
the consumer, but it will also help reduce waste for growers since fewer potatoes will be
discarded.
The second trait is a reduction in reducing sugars through down-regulation of phos-
phorylase and starch associated genes, slowing the conversion to sucrose and fructose,
which provides potatoes with a consistent golden color that results in improved taste
and texture qualities. The third trait is suppression of asparagine through expression of
asparagine synthetase-1, which reduces the potential for the formation of acrylamide by
80%. The latter is created when potatoes are cooked at high temperatures. By reducing
the levels of these sugars and asparagine in stored potatoes, they can significantly lower
the levels of acrylamide in the food. Accordingly, this modification improves not just the
quality but also the safety of the potato by reducing levels of this toxic chemical.
Other antinutrients that are being examined as possible targets for reduction are tryp-
sin inhibitors, lectins, and several heat-stable components found in soybeans and other