Barley for Food and Health: Science, Technology, and Products

GLYCEMIC RESPONSE TO CARBOHYDRATE CONSUMPTION 187
clearly demonstrated that the absorption of carbohydrate from the PW barley
was significantly lower than that of the standard barley, presumably due to the
concentration of β-glucan and its attendant viscosity and delay in absorption.
An Australian group (Keogh et al. 2007) tested the high-amylose barley
Himalaya 292 (renamed BarleyMax) and wheat, formulated into meals for healthy
lean women in a crossover study to determine glycemic responses and satiety
effects. The mean areas under the curve in response to wheat-containing meals
were 22 and 32% higher than those for barley-containing meals for glucose and
insulin, respectively. In this study, the barley meals did not reduce spontaneous
food intake, despite its reduced glycemic and insulinemic effects.
A β-glucan concentrate, Nu-trimX, developed from an extract of PW barley,
and a similar product from oats (Inglett 2000) were tested for glucose and insulin
responses by Hallfrisch et al. (2003) at the USDA Human Nutrition Research
Center in Beltsville, Maryland. Healthy men and women consumed test meals
containing a pudding with either oat bran, barley flour, oat Nu-trimX, or barley
Nu-trimX, with glucose as a control. The area under the blood glucose curve was
lowest for the barley extract, but not significantly different from other β-glucan
sources, which were all lower than the glucose control. These researchers concluded
that extracted hydrocolloids extracted from oats and barley retain the
beneficial effects of the original whole grains. Barley β-glucan extract provided
lower glucose and insulin curves than resistant starch in muffins (Behall et al.
(2006b). In that study there were two groups of male subjects, normal weight
and overweight, and the latter exhibited higher blood glucose increments after
consuming the test muffins. However, in an earlier similar study with women,
β-glucan and resistant starch produced similar glycemic responses (Behall et al.
2006a). Poppitt et al. (2007) investigated the glycemic effect of a high barley
supplement (Cerogen) added to solid foods and to a beverage. The supplement
improved glucose control when added to solid foods, but not when consumed
as a beverage. Researchers attributed the results to the lack of viscosity of the
supplement in liquid form, which is indicative of enzymatic hydrolysis of the
β-glucan. This phenomenon is commonly observed when barley is moistened
without destroying the endo-β-glucanases.
The USDA Western Regional Center at Albany, California also conducted
studies on the glycemic effects of barley foods (pasta). Using a procedure of
milling and sieving (Knuckles et al. 1997), Yokayama et al. (1997) prepared a
β-glucan-enriched flour from the hulless, waxy Waxbar barley, containing 32%
TDF and 20.1% β-glucan. Pasta made from a blend of the barley flour and
wheat flour contained 7.7% β-glucan. Healthy subjects consumed the pasta in
meals containing 100 g of available carbohydrate, using an all-wheat pasta as a
control. The barley pasta resulted in a lower glycemic response as measured by
average total area and maximum increment of the blood glucose curves. Lower
insulin responses to the barley pasta were also observed. This research group
conducted a second pasta study in which two barley cultivars were compared
(Bourdon et al. 1999). Pasta was prepared by replacing 40% of wheat flour with
either Waxbar barley flour enriched in β-glucan as in the previous study, or