Native, modified and clean label starches in foods and beverages - Natural Food Additives, Ingredients and Flavourings - page 165

of glucose units. These two polymers occur in differing amounts in starches from
various botanical sources. Amylose is responsible for gelling properties and shear
resistance, while amylopectin is responsible for stability.

7.4.1 Amylose
Amylose is a linear polymer containing up to 6000 glucose units, connected by
1,4-linkages (Fig. 7.2).
The ratio of amylose to amylopectin is fairly constant for a given species of
starch. Maize and sorghum starch have a much higher amylose content (about
28%) than the tuber and root starches (potato, tapioca, arrowroot), which contain
only about 20% amylose. The waxy starches contain no amylose fraction.
Amylomaize starch, a maize starch, which has been selectively bred so that the
resultant starch has a high amylose content, may contain up to 80% amylose. It is
largely used in edible fi lms, coatings and biodegradable packaging. Amylose
covers a range of degrees of polymerisation, depending upon the source of the
starch. The amylose molecules of potato and tapioca starch have a substantially
higher molecular weight than maize and wheat starch amylose.
The amylose fraction of potato starch has a DP ranging from 840 to 22 000
glucose units. The amylose fraction of maize starch has a DP of about 400-15 000
glucose units.
Amylose forms inclusion complexes with iodine and various organic
compounds such as butanol, fatty acids, various surfactants, phenols and
hydrocarbons. These complexes are essentially insoluble in water. It is believed
that amylose complexes by forming a helix coil around the complexing agent. The
complex of amylose with iodine gives a characteristic blue colour, which is used
to establish the presence of amylose-containing starch.

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Fig. 7.2 Linear structure of amylose molecule.