Barley Cultivar, Kernel Composition, and Processing Affect the Glycemic Index

Abstract

Barley has a low glycemic index (GI), but it is unknown whether its GI is affected by variation in carbohydrate composition in different cultivars and by food processing and food form. To examine the effect of these factors on GI, 9 barley cultivars varying in amylose and β-glucan content were studied in 3 experiments in separate groups of 10 healthy participants. In Expt. 1, 3 barley cultivars underwent 2 levels of processing: hull removal [whole-grain (WG)] and bran, germ, and crease removal [white pearled (WP)]. GI varied by cultivar (CDC Fibar vs. AC Parkhill, [mean ± SEM]: 26 ± 3 vs. 53 ± 4, respectively; P < 0.05) and pearling (WG vs. WP: 26 ± 4 vs. 35 ± 3, respectively; P < 0.05) with no cultivar × pearling interaction. In Expt. 2, the GI of 7 WG cultivars ranged from 21 ± 4 to 36 ± 8 (P = 0.09). In Expt. 3, WG and WP AC Parkhill and Celebrity cultivars were ground and made into wet pasta. The GI of AC Parkhill pasta (69 ± 3) was similar to that of Celebrity pasta (64 ± 4) but, unlike in Expt. 1, the GI of WP pasta (61 ± 3) was less than that of WG pasta (72 ± 4) (P < 0.05). Pooled data from Expts. 1 and 2 showed that GI was correlated with total fiber (r = -0.75, P = 0.002) but not with measures of starch characteristics. We conclude that the GI of barley is influenced by cultivar, processing, and food form but is not predicted by its content of amylose or other starch characteristics.

Wholegrain barley β-glucan fermentation does not improve glucose tolerance in rats fed a high-fat diet

“…These findings are consistent with those of Liljeberg et al [43] who showed that, when breads are matched for insoluble fiber (12.1%-13.6%), increasing their β-glucan content from 11% to 15% did not affect the acute glycemic response in healthy adults. Aldughpassi and colleagues [44] also came to a similar conclusion when they investigated the glycemic impact of a range of different barley varieties and showed that the most significant characteristic that correlated with GI was grain total dietary fiber content (r = −0.75, P = .002) rather than β-glucan content (r = −0.44, n = 14, P = .11). These studies suggest that, unlike β-glucan isolates, wholegrain- Values are means ± SEM.…”

Review of human studies investigating the post-prandial blood-glucose lowering ability of oat and barley food products

“…Food formats Intact boiled kernels were used in six studies, as is, fermented, pearled or baked into wheat bread. 9,29,32,36,43,44 Where the integrity of the kernel was maintained, 96% (21/22) treatments showed efficacy with an average reduction in AUC of 99±20 mmol Á min/l. The glycaemic response to intact boiled barley was shown to be related to total dietary fibre and slowly digestible starch, rather than b-glucan content.…”

“…The glycaemic response to intact boiled barley was shown to be related to total dietary fibre and slowly digestible starch, rather than b-glucan content. 32 This difference from processed products suggests that, for cooked kernels, the intact cell walls act as a physical barrier to starch-degrading enzymes.…”

Quantification of amylose, amylopectin, and β-glucan in search for genes controlling the three major quality traits in barley by genome-wide association studies

“…High β-glucan and waxy phenotypes are regarded unfavorable for brewing and feed stuff, but they are considered to be a valuable source of soluble fiber in human diets showing potential functions in reducing GI and serum cholesterol levels, flattening the postprandial blood glucose levels and insulin rises (Thondre and Henry, 2009; Ahmad et al, 2012). The ability of β-glucan to lower the GI is dependent on the barley starch type (Finocchiaro et al, 2012) and other grain chemicals, especially the total content of fiber (Aldughpassi et al, 2012). …”