Food Microstructure and Starch Digestion - Advances in Food and Nutrition Research - page 161

The high level of viscosity slows down many of the physiological pro-
cesses associated with the digestion of foods and absorption of nutrients
and thus helps in improving the management of glucose intolerance and
obesity. The well-documented blood glucose-reducing effect of dietary
supplements of water soluble nonstarch polysaccharides such as pectin
and guar gum also depends on their capacity to increase viscosity of dig-
esta in the stomach and the small intestine ( Johansen, Knudsen,
Sandstr¨m, & Skjøth, 1996 ) . Gastric response to increased meal viscosity
has been assessed by techniques such as echo-planar magnetic resonance
imaging ( Marciani et al., 2000 ).
4.1. Rheology (flow behavior) of digesta
Detailed measurements on the viscosity of cooked potatoes (with or with-
out the addition of gum) during in vitro small intestinal digestion were
recorded by Bordoloi, Singh, et al. (2012) using a dynamic rheometer
( Figs. 4.15 and 4.16 ). The viscosity of cooked potatoes dropped consider-
ably as SIF is added, due to conversion of highly viscous starch in potatoes
to low-viscosity sugars by the digestive enzymes present in SIF ( Fig. 4.16 ) .
However, the viscosity stayed stable afterward during the whole course of
simulated small intestinal digestion of cooked potatoes.
The addition of guar gum resulted in an increase in viscosity of the cooked
potatoes, which could mainly be attributed to the viscosity imparted by the
guar galactomannan that stabilized the structure ( Fig. 4.15 ) . The viscosity
of cooked potato-guar gummixture was more than 1 Pa throughout the time
sweep experiment. The increase in viscosity can affect gastric function and
may inhibit propulsive and mixing effects generated by peristalsis during
in vivo digestion ( Ellis et al., 1995 ). The viscosity of cooked potato-guar
gum mixture was decreased when SIF (containing enzymes) was added
( Fig. 4.16 ). However, the extent of decrease in viscosity was far less than that
observed for cooked potato only samples. The curves for the control cooked
potato sample and cooked potato-guar gum sample (containing SIF with
enzymes) overlap each other ( Fig. 4.16 ) . The significant decrease that
occurred during the digestion of cooked potato only sample was balanced
by the presence of gum that facilitated the matrix to maintain a stable viscosity.
Also, in the presence of gums, the interactions between substrates and diges-
tives enzymes are less frequent, which could be another reason for a less
decrease in viscosity. This may result in a decreased rate of starch digestion
and ultimately a slower absorption of the hydrolysis products (e.g., maltose,