Corn, like most grain crops, is grown mostly for carbohydrates as a source of energy. Most of the carbs are stored as starch in the endosperm component of the kernel. Protein, which makes up only about 8-9 percent of the kernel, is mostly located in the embryo. Grain starch is composed of two types, both being composed of glucose molecules. Glucose is a relatively simple molecule composed of 6 carbon, 12 hydrogen and 6 oxygen atoms. Amylose type starch is mostly a linear string of several hundred glucose units. Amylopectin, the other type of starch component, is a more branched but shorter type of starch. The two types of branching result in differences in ease of digestion, amylopectin being easier to digest apparently because of the shorter structure. Amylose appears to be a little more efficient for storage in plants because of its linear structure. The differences in the two types of structure affects their properties as well. Amylose tends to be less soluble in water and can act as a binding agent in gels. Amylose does bind with iodine, causing a blue color when exposed to iodine. Most dent corn hybrid starch is about 25% amylose and 75% amylopectin.
A single recessive gene can cause corn to produce mostly amylose starch, with some modifier genes affecting the actual percentage. Because it involves a recessive gene, both parents of the hybrid must be homozygous for the recessive gene and the hybrid field must be isolated from normal corn to maintain the purity. Waxy corn starch is totally amylopectin and also controlled by a single recessive gene. Consequently, both parents of the hybrid must be homozygous for this recessive gene and isolation of the hybrid field is needed to keep the grain quality. Amylopectin does not stain blue with iodine. Both types of starches have separate commercial uses.
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About Corn Journal
The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.