due to penetration of water molecules into its branched
structure. As mentioned above, long boiling makes it dissolve
in water or in weak acids, as well as in solutions with hydroxides
of potassium, rubidium, cesium, or francium and concentrated Studies
on starch include examination of water absorption, chemical
modifi cation of molecules, behavior under agitation, and
high-temperature thermomechanical abrasion resistance.
Although starch is a polymer, its strength under stress appears
to be low. At temperature above 150°C, the glycoside bonds
start cracking and over 250°C starch granules subside endothermally.
At low temperatures, however, some reorganization
of hydrogen bonds is observed together with straightening of
the molecule chains during the cooling process (retrogradation).
In some extreme cases, under 10°C, precipitation is
reported. Starch may be hot water soluble and formed in thin
films; its molecular orientation causes brittleness in both foils
and solid packages. Both amylose and amylopectin consist of
glucopyranosis molecules, yet the structural differences between
these two polymers determine their different properties. Amylose
is mostly a linear polymeric molecule, consisting of α-1,4-
linked D-glucopyranose (Fig. 4). The molecular weight
of amylose varies from 500 anhydroglucose units in highamylose
maize starch to more than 6,000 anhydroglucose
units in potato starch
solutions of chloral hydrate. Soluble starch (amylum
solubile) is obtained as a result of long boiling of starch with
water or weak acid; link cleavage at the amylopectin chain
branching sites is then observed, and eventually a watersoluble
product is formed. It is employed as an indicator in
chemical analysis.