Waxy
Maize, a genetically drifted (mutated) variety of normal
dent corn
was first identified in China in 1909. The endosperm of waxy maize was found to
contain only amylopectin and no amylose in opposition to normal dent maize
varieties that contain both. The starch Amylopectin is heavily used in food
products, in the textile, adhesive, corrugating and paper industry.
Commercially
prepared Waxy Maize products are nothing more than corn starch from a distinct
variety of maize that only bears amylopectin as its storage carbohydrate.
Amylopectin is a highly
branched polymer of glucose found in plants. It is one of the two components of
“normal” starch, the other being amylose. Amylopectin is soluble and highly stable in water. Starch is made
of about 70% amylopectin by weight. Amylopectin is highly branched, being
formed of 2,000 to 200,000 glucose units. Its counterpart in animals is
glycogen which has the same composition and structure, but with more extensive
branching that occurs every 8 to 12 glucose units.
With
a relatively rapid transport and early digestion AP (amylopectin) becomes
available as plasma blood sugar more quickly than most other “starch” sources.
Despite its rapid onset and large molecular structure AP consistently shows a
moderate to high glycemic index rating on most charts.
History of Waxy Maize
The
first mentions of Waxy Maize were found in the archives of the U.S. Department
of Agriculture. In 1908, the Rev. J. M. W. Farnham, a Presbyterian missionary
in Shanghai, sent a sample of
seeds to the U.S. Office of Foreign Seed and Plant Introduction. A note with
the seeds called it: “A peculiar kind of corn. These seeds were planted on May 9, 1908, near Washington, D.C., by a botanist named G.N. Collins. He was able to grow
53 plants to maturity and made a thorough characterization of these plants,
including photographs, which were published in a USDA bulletin issued in
December 1909.
In
1922, another researcher, P. Weatherwax of Indiana University in Bloomington,
reported that the starch in waxy maize was entirely of a “rare” form called
“erythrodextrin”, known today as amylopectin. He found that this rare starch
stained red with iodine, in contrast to normal starch which stained blue.
Bates, French et al. and Sprague, Brimhall, et al. confirmed that
endosperm starch of waxy maize consists nearly exclusively of amylopectin.
Biology
Experiments
have shown that ten to twenty plants are required for adequate representation
of genetic diversity in an open-pollinated maize variety. Since the number of
ears saved for seed by ancient Asian maize cultivators with only small plots of
land at their disposal was often smaller than this and, indeed, since new maize
populations are sometimes established by growing the progeny of a single ear,
it follows that there must often have been a high potential for genetic drift
(changes in gene frequencies resulting from the creation of small breeding
populations).
Genetics
A
single recessive gene (wx), located on the short arm of chromosome 9, codes for
the waxy endosperm of the kernel (Wx codes for endosperm with normal starch).
This was first shown by Collins and Kempton.
Characterization with iodine
Amylose
and amylopectin have different iodine binding-properties, with maize amylose
and amylopectin giving iodine affinity (IA) values of about 19 to 20 and 1%,
respectively, depending upon the source. The amount of apparent amylose can be
determined either by measuring the absorbency of the starch-iodine complex
(blue-value) and relating this value to that of pure amylose and amylopectin
standards or by measuring the amount of iodine (mg) bound per 100 mg of
starch in a potentiometric titration and relating the value to the amount bound
by an amylose standard. Values used on the iodine binding, however, are only
estimates of amylose content because of differences in the binding abilities
(and structure) of amylose and amylopectin among starch types.
Biochemistry
Normal
dent maize has two different pathways for starch formation: one leading to
branched chain (amylopectin) and the other to straight-chain polysaccharides
(amylose). The amylopectin consists of chain of α-D-(1-4)
and α-D-(1-6)-glucosidic
linkages that form a branched molecule. Amylose is primarily linear with α-D-(1-4)-linked
glucose residues.
Agronomic features
Growing
maize with pure amylopectin starch is not easy. The waxy gene being recessive,
the waxy maize has to be isolated from any nearby normal maize field by at
least 200 meters.
Amylopectin:
industrial uses
Starch
is the reserve carbohydrate in the plant kingdom. Although starch occurs
throughout the plant world, there are only a few plants used to produce it
commercially, and maize is the major source of starch produced world-wide. At
the second range comes potato, then wheat and to a lesser extent rice. Maize
starch was first produced in the U.S. in 1844 at the plant owned by William
Colgate.
The
amylopectin yield of the kernel ranges from 58.5 to 69% (of dry solid mass).
Wet-milling waxy maize results in starch yields that are only 90% of those of
dent maize. The wx starch is relatively easy to gelatinize and produces a clear
viscous paste with a sticky or tacky surface, rather than one with sharp edges.
This paste resembles pastes of root or tuber starches, such as potato or
tapioca. Most starches in their native or unmodified form have limited use in
various industries. Therefore, most starches including waxy maize starch are
modified either to improve or repress their inherent properties as may be
required for special use applications. Many types of modified waxy starches
have a multitude of applications in the paper, textile, corrugating, and
adhesive industries in addition to an enormous array of application in the food
industry.
Food
products
Modified
waxy maize starches serve essential functions in foods, including the
improvement of uniformity, stability, and texture in various food products. The
clarity and stability of amylopectin starch make it especially suitable for
thickening fruit pies. It improves smoothness and creaminess of canned food and
dairy products as well as freeze-thaw stability of frozen foods. It gives a
more desirable texture and appearance to dry foods and mixes. Waxy maize starch
is also the preferred starting material for the production of maltodextrins
because of improved water solubility after drying and greater solution
stability and clarity. As of recent, the dietary supplement industry has seen
an increase in the usage of Swedish Waxy Maize Starch. WM starch does have a
moderate to slow Glycemic index; however, it is its unique osmolity that allows
it to pass through the digestive system relatively quickly.
Livestock,
dairy and poultry feeding
The
feeding of waxy maize began in the 1940s. Beginning with a research report in
1944, waxy maize seemed to have the potential to increase feed conversion
efficiencies. Manyother feeding trials involving swine, beef and dairy cattle,
lambs and poultry were designed to compare the feeding value of waxy to normal
dent grain. Generally, the trials indicated an advantage for feeding waxy
grain. Seldom have the investigations shown any negative or adverse effects
from feeding waxy grains. Increases of both milk production and butterfat
content are not uncommon when waxy maize is fed to lactating dairy cattle.
Increases of more than 20% in average daily weight gains in fattening lambs
were observed when waxy grain was compared with normal dent. In addition, a 14%
increase in feed efficiency was noted in favor of waxy grain. Likewise an
increase in feed efficiency approaching 10% was obtained in trials where waxy
grain was compared with the dent counterparts when fed to finishing beef
cattle.
Conclusion
Waxy
Maize is a great source of Amylopectin! What value
a high molecular weight high GI starch is to body composition is a lot less
certain! Sucrose and Dextrose have a dollar cost in the range of ten percent of
commercial WM products and offer equal (or similar) Kcal/g and GI profiles.
Amylopectin (WM) could have applications under extremely controlled conditions
like pre-contest carb-up. Off season carb sources are vast and relatively low
in cost making WM a hard sell in my view.
