Biology Reference
In-Depth Information
formulation. Both these components interact with starch during processing
and influence the rate of glucose formation during starch digestion.
Our chapter presents a detailed discussion on the above-mentioned fac-
tors that control the digestibility of starch in natural as well as processed
foods. This includes a review of the recent information on food microstruc-
ture, viscosity, composition of food, processing techniques, and their rela-
tionship with starch digestion.
2. STARCH DIGESTION
Starch is mainly hydrolyzed by the mammalian amylolytic enzymes into
glucose through several steps. Salivary
-amylase acts quite efficiently on
starch in mouth but is rapidly inactivated and degraded in the acidic environ-
ment of the stomach and hence plays a very minor role in the process of starch
digestion. Starch-degrading enzymes are present in digestive fluids as well as in
the brush border of the small intestine
(
Smith & Morton, 2001
). Majority of
the starch hydrolysis is carried out by the pancreatic amylase, which is released
in the small intestine via pancreatic duct.
a
a
-Amylase catalyzes the hydrolysis
(endo attack) of
-(1-4)glycosidic bonds in amylose and amylopectin of starch
(
Lehmann & Robin, 2007
). Both the linear and branched (amylose and amy-
lopectin) polymers of starch are hydrolyzed by virtue of binding of their five
glucose residues adjacent to the terminal reducing glucose unit to specific cat-
alytic subsites of the
a
a
-amylase, followed by cleavage between the second and
third
-1,4-linked glucosyl residue
(
Gray, 1992
)
. The final hydrolysis prod-
ucts from amylose digestion are mainly maltose, maltotriose, and mal-
totetraose. However,
a
-amylase from some microbial sources may produce
maltohexose and maltoheptose along with maltotriose (
Yook & Robyt,
a
-1,6 branch linkage in amylopec-
tin; therefore, its capacity to break
a
-1,4 links adjacent to the branching point
is decreased mainly due to steric hindrance. The results obtained from the
analysis of intestinal content of humans suggest that hydrolysis products from
amylopectin mainly consist of dextrins or branched oligosaccharides. The
products obtained from
a
-Amylases have no specificity for
a
a
-amylase starch hydrolysis have been observed to
possess
-anomeric configuration of the substrate
(
Kuriki & Imanaka,
a
-dextrins)
are further hydrolyzed efficiently by the action of brush border enzymes of
the intestine. The enzymes present in the human body are difficult to extract
or expensive to buy; therefore, enzymes from other mammals or from
a
