Inherent properties of starch
Crystallinity of starch. One of the causes of resistance to enzymes
is the crystallinity of native type B starch granules as observed
in the case of amylomaize starch and also the encapsulation
of starch within plant cell or tissue structures. X-ray diffraction
and differential scanning calorimetry studies on crystalline residues
from amylomaize starch samples have suggested that chain
fragments packed in a type B crystalline structure with a slightly
enlarged crystal lattice contribute to formation of RS from amylomaize
starch. Any treatment that eliminates starch crystallinity
(that is, gelatinization) or the integrity of the plant cell or tissue
structure (that is, milling) increases enzyme availability and reduces
the content of RS, whereas recrystallization and chemical modifications
tend to increase the RS. The modified food starches are
partially resistant to enzymes as a result of chemical modifications
induced intentionally (Englyst and Cummings 1986; Bjorck and
others 1989; Schweizer and others 1990). Besides these, the cellular
structure of plant foods influences the digestibility of starch
in the small intestine as well as the intrinsic digestibility of a particular
physical form of starch.