MOLECULAR STRUCTURE OF CORN STARCH
Amylose is a linear polymer of short 1,4 linked glucose chains. Typically the amylose fraction is about 25-30%
of the starch molecules found in corn and has a molecular weight of about 250,000. The percentage of
amylose in the starch is genetically determined. Genetic modifications producing high-amylose (50-70%)
cornstarch are also found. Amylopectin comprises about 70-75% of the starch found in the corn kernel and
has a molecular weight of about 50-500 million. Amylopectin is a branched polymer of the basic repeating
units of 1,4 linked glucose with branches of 1,6 linked glucose. The branching occurs irregularly in the
starch, approximately one per twenty-five glucose units.
AMYLASES
Amylases are a class of enzymes that are capable of digesting these glycosidic linkages found in starches.
Amylases can be derived from a variety of sources. Amylases are present in all living organisms, but the
enzymes vary in activity, specificity and requirements from species to species and even from tissue to
tissue in the same organism. Alpha-amylase (1,4 aD-Glucan-glucanohydrolase) acts upon large polymers
of starch at internal bonds and cleaves them to short glucose polymers. a-amylase catalyzes the hydrolysis
of internal a1-4 glucan bonds in polysaccharides containing 3 or more a1-4 linkages; it results in a mixture
of maltose and glucose. Amyloglucosidase works on the shorter polymers and splits off single glucose
sugars. Bacterial a-amylase is particularly suited for industrial usage since it is inexpensive and is
thermally stable.