Biology Reference
In-Depth Information
1. INTRODUCTION
Poor control of impaired fasting glucose and impaired glucose toler-
ance is associated with an increased risk of developing diabetes mellitus,
which is a major health threat that is impacting more than 10% of the pop-
ulation worldwide (
WHO, 2009
). For diabetic patients, effective control of
postprandial hyperglycemia is a challenge and low glycemic index (GI) diets
are suggested as a feasible solution (
Sheu et al., 2011
)
. While high pressure
processing was supposed to significantly change some physicochemical
properties of several native starches and reduce their digestibility
(
Le Thanh-Blicharz, Bialas, & Lewandowicz, 2009
)
, the inclusion of small
molecule starch hydrolase inhibitors from edible plants could be another
practical and economical route to reduce starch digestibility. In this chapter,
we summarize the recent advances made in the discovery of novel inhibitors
for starch hydrolases. In the first two parts, we describe the natural products
isolated from edible plants and their starch hydrolase inhibition activity.
A list of
a
-glucosidase and
a
-amylase inhibitors from natural plants is given
in
Table 3.1
. The second part, recent progress summarized on low GI foods
incorporated with ingredients from plants containing starch hydrolase inhib-
itors is described.
The enzymes involved in starch digestion include
a
-amylase (saliva and
pancreatic) and
a
-glucosidase bound on the small intestine surface. Both
enzymes catalyze hydrolysis reaction via conjugated acid-based catalysis,
but they have distinct substrate-binding sites.
a
-Amylase has a long grove
filled with amino acid residues that can form multiple hydrogen bonds with
oligosaccharides (
Larson, Day, & McPherson, 2010
), whereas the substrate-
binding sites for
a
-glucosidase are much smaller. The structural difference of
the two enzymes enables selectivity of the inhibitors.
Since the substrates of the two enzymes are not the same methods used to
measure their enzymatic activity and inhibitor activity are also different. For
a
-amylase, the most widely used assay is Dinitrosalicylic acid (DNSA) assay,
which is nonselective toward reducing ends of oligosaccharides formed in
is mainly glucose and coupled enzyme assay using glucose oxidase and per-
oxidase was commonly used in quantification of inhibition activity (
Fox &
Robyt, 1991; Watanabe, Kawabata, Kurihara, & Niki, 1997
). In addition,
synthetic chromogenic molecular probes such as
p
-nitrophenyl-glucoside
(pNPG) are also adopted because of the convenience in measuring both
