74
containing a part of non-digestible starch decreases levels of glucose and insulin in
blood, compared to foods containing same levels of completely digesting starch
(Bornet et al. 1989). RS is utilized and acted upon by the microflora of the large
intestine, which causes it to ferment and results in the production of hydrogen,
methane, and SCFA (mainly propionic, acetic and butyric acid) thereby lowering
lumen pH. The resulting pH helps in selective screening of intestinal microflora,
eliminating pathogenic microorganisms and stimulating growth of beneficial bacteria. The acids formed in the large intestines demonstrate health-promoting activity.
The amount of butyric acid formed upon fermentation of RS is higher than that
produced as a result of non-starch polysaccharide fermentation and plays an important role in prevention of anal and colorectal cancers.
In order to be identified as prebiotic RS has to fulfill the following criteria:
I. Resistance to gastric acidity, hydrolysis by mammalian enzymes and absorption in the upper gastrointestinal tract;
II. Fermentable by probiotic microbiota, especially lactobacilli and
bifidobacteria,
III. Selectively stimulate activity and/or growth of gut bacteria that contribute to
host health and wellbeing.
Criteria I
Structural characteristics are responsible for the resistance of RS. The ratio of amylose to amylopectin being one of the main characteristics that contributes to the
resistance of starch. The entangled arrangement between these molecules (amylase
and amylopectin) holds the integrity of starch granules. It has been demonstrated
that enzymatic digestibility of starch decreases as amylose to amylopectin ratio
increases (Jane 2006). The amylase-amylopectin interaction makes the starch inaccessible to hydrolytic enzymes by preventing the starch from swelling. Another
starch characteristic that could influence its digestibility is the lipid content. The
amylase-lipid complexes exhibit resistance to hydrolysis by amylase enzyme.
Formation of such complexes restricts swelling of starch and retard the enzymatic
hydrolysis of starch granules (Jane and Robyt 1984; Morrison 2000). In addition,
the presence of lipid on the surface of starch granules can contribute to their resistance (Morrison 1981, 1995).
Criteria II
For a RS to be regarded as a prebiotic, it must be used as a substrate for fermentation
by gut microflora and confer health benefits to the host. Bacterial fermentation that
occurs in the human gut are of two types viz., saccharolytic and proteolytic. As the
names suggest, the saccharolytic bacteria break down the carbohydrates and are
dominant in proximal colon, whereas, proteolytic bacteria are responsible for
M. Ahmad et al.
containing a part of non-digestible starch decreases levels of glucose and insulin in
blood, compared to foods containing same levels of completely digesting starch
(Bornet et al. 1989). RS is utilized and acted upon by the microflora of the large
intestine, which causes it to ferment and results in the production of hydrogen,
methane, and SCFA (mainly propionic, acetic and butyric acid) thereby lowering
lumen pH. The resulting pH helps in selective screening of intestinal microflora,
eliminating pathogenic microorganisms and stimulating growth of beneficial bacteria. The acids formed in the large intestines demonstrate health-promoting activity.
The amount of butyric acid formed upon fermentation of RS is higher than that
produced as a result of non-starch polysaccharide fermentation and plays an important role in prevention of anal and colorectal cancers.
In order to be identified as prebiotic RS has to fulfill the following criteria:
I. Resistance to gastric acidity, hydrolysis by mammalian enzymes and absorption in the upper gastrointestinal tract;
II. Fermentable by probiotic microbiota, especially lactobacilli and
bifidobacteria,
III. Selectively stimulate activity and/or growth of gut bacteria that contribute to
host health and wellbeing.
Criteria I
Structural characteristics are responsible for the resistance of RS. The ratio of amylose to amylopectin being one of the main characteristics that contributes to the
resistance of starch. The entangled arrangement between these molecules (amylase
and amylopectin) holds the integrity of starch granules. It has been demonstrated
that enzymatic digestibility of starch decreases as amylose to amylopectin ratio
increases (Jane 2006). The amylase-amylopectin interaction makes the starch inaccessible to hydrolytic enzymes by preventing the starch from swelling. Another
starch characteristic that could influence its digestibility is the lipid content. The
amylase-lipid complexes exhibit resistance to hydrolysis by amylase enzyme.
Formation of such complexes restricts swelling of starch and retard the enzymatic
hydrolysis of starch granules (Jane and Robyt 1984; Morrison 2000). In addition,
the presence of lipid on the surface of starch granules can contribute to their resistance (Morrison 1981, 1995).
Criteria II
For a RS to be regarded as a prebiotic, it must be used as a substrate for fermentation
by gut microflora and confer health benefits to the host. Bacterial fermentation that
occurs in the human gut are of two types viz., saccharolytic and proteolytic. As the
names suggest, the saccharolytic bacteria break down the carbohydrates and are
dominant in proximal colon, whereas, proteolytic bacteria are responsible for
M. Ahmad et al.