Biology Reference
In-Depth Information
low-viscosity
b
-glucan for improvement in glucose tolerance and insulin
sensitivity. When beverages formulated to supply 3 g or 6 g/day
b
-glucan
were supplied to overweight and obese individuals for 12 weeks, there
was a significant reduction in the glucose area under the curve following
an oral glucose tolerance test, fasting insulin values, and also insulin resistance
at the end of the intervention period
(
Bays et al., 2011
). In addition to the
b
-glucan content in barley, the proportion of amylose and amylopectin has
also been reported to be responsible for its low GI (
King, Noakes, Bird,
Morell, & Topping, 2008
)
. A high-amylose barley called Himalaya 292 with
high-fiber content was prepared into a breakfast cereal and compared with a
traditional commercial barley cereal with three times less fiber content.
When tested in healthy subjects, the GI of Himalaya 292 was 50 compared
to 77 for the commercial barley cereal. Moreover, the high-amylose barley
cereal reduced insulin response by 26% compared with the commercial bar-
ley cereal thereby substantiating its use in prevention and management of
type 2 diabetes. This high GI for a commercial barley cultivar is not expected
because barley is often referred to as a low-GI cereal. The same cereal
Himalaya 292 was used in preparing bread and muffin and compared with
similar test meals made of wheat in an earlier study (
Keogh et al., 2007
).
However, this study did not show a significant effect on blood glucose
but showed a significant lowering of insulin response in healthy subjects.
These differences may have been due to the difference in food matrices,
and the presence of other ingredients in making bread and muffin compared
to just preparing a breakfast cereal. The beneficial effect of amylose on blood
glucose response is due to its structural characteristics as a linear polymer of
glucose less susceptible to gelatinization compared to the branched polymer
amylopectin. Amylose also quickly undergoes retrogradation during cooling
resulting in slow digestion and absorption. The type of starch with low amy-
lose content is often termed as waxy starch. The use of normal and waxy
starch from barley has also been tried in bread-making to evaluate their gly-
cemic response.
Finocchiaro et al. (2012)
substituted 40% of wheat flour
with the barley flour and found that in the presence of low amylose starch,
the effect of
b
-glucan (6%) was not evident on the glycemic response of
bread. The normal starch barley with the same amount of
b
-glucan (6%)
reduced the GI of the bread while the waxy starch barley did not do so in
the presence of
b
-glucan. This showed that even in the presence of
b
-glucan,
the type of starch and the proportion of amylose and amylopectin have an
important role in determining the glycemic response to food items such as
bread.
