Food Microstructure and Starch Digestion - Advances in Food and Nutrition Research - page 158

et al., 2010; Henry & Lightowler, 2009; Singh et al., 2010 ) . The physical
texture of the food may affect the digestion of starch and the absorption
of hydrolysis products. Plant-derived polysaccharides such as gums are used
in food products as a thickening, emulsifying, and stabilizing agent, and also
because of their beneficial effects as soluble dietary fiber ( Williams & Phillips,
2003 ). Soluble dietary fiber like guar gum has the ability to produce high
viscosity (at low concentration), thereby, significantly affecting the nutrient
absorption and postprandial plasma nutrient levels in the gut ( Cherbut,
Albina, Champ, Doublier, & Lecannu, 1990; Eastwood & Morris, 1992;
Edwards, Johnson, & Read, 1998; Ellis, Rayment, & Wang, 1996 ). The
presence of galactomannan-based gums also imposes restrictions on the
availability of water molecules, swelling or gelatinization of starch granules
and reduces the size of granule remnants in the starch paste, if cooked
together ( Kaur & Singh, 2009; Kaur, Singh, Singh, & McCarthy, 2008 ).
Bordoloi, Singh, et al. (2012) reported that the addition of guar gum
(0.5%) to the cooked potato matrix led to a significant decrease in both
the rate and the extent of final starch hydrolysis ( Fig. 4.14 ). A drop of

20% in the overall starch hydrolysis (to that of the control) was observed
after first 15 min of hydrolysis under simulated intestinal conditions, when
guar gum was added. Guar gum also affects the final hydrolysis of the starch
significantly ( p < 0.05), with

15% drop in hydrolysis at the end of the sim-
ulated digestion period. The rate and extent of starch hydrolysis in the small
intestine are dependent upon several intrinsic and extrinsic factors ( Englyst
et al., 1992 ). Gums have been reported to produce high viscosity in the gut
lumen, which in turn influence the nutrient absorption and postprandial
plasma nutrient levels ( Edwards, 2003 ) . The slower rate of starch hydrolysis
in the presence of guar gum could be attributed to the increase in viscosity of
the digesta due to enlargement of fully hydrated galactomannan chains of
guar gum ( Ellis, Roberts, Low, & Morgan, 1995 ) . Dartois et al. (2010)
reported that the gum layer around the starch granules could limit access
of enzymes to starch, consequently decreasing the enzymatic starch hydro-
lysis. Hydrocolloids have been reported to form a continuous network by
suspending the starch matrix in a coherent gel, which acts as a barrier toward
the access of enzymes to starch ( Koh, Kasapis, Lim, & Foo, 2009 ). Thus, guar
gum may act as a physical “barrier” toward the interactions of digestive
enzymes and starch and/or to the release of hydrolysis products into the
aqueous phase of the digesta. This was also evidenced from the hydrolysis
levels observed immediately after the addition of simulated intestinal
juices in the study of Bordoloi, Singh, et al. (2012) . The hydrolysis levels