Physiological Effects of Barley: Examining the Effects of Cultivar, Processing and Food Form on Glycemia, Glycemic Index, Satiety and the Physico-chemical Properties of β-glucan

Barley has been receiving increased attention as a human food due to the health benefits associated with β-glucan fiber and its potential as a low glycemic index (GI) functional food. Research has shown a relationship between the physico-chemical properties of β-glucan and the physiological effects, which may be altered by processing. However, it is not known if the physiological effects of consuming barley are affected by variations in chemical composition among cultivars or by common processing methods such as pearling or milling. The primary objective of this thesis was to characterize the effects of differences in cultivar starch and fibre content, level of pearling and milling on the GI, satiety and the physico-chemical properties of β-glucan. Nine barley cultivars varying in starch-type and β-glucan content were studied in three experiments in separate groups of ten healthy participants. Blood glucose and satiety ratings were measured and the GI was calculated. Total starch, total fibre, β-glucan, molecular weight (MW), solubility and β-glucan viscosity were determined in vitro. Results showed that GI varied by cultivar (CDC-Fibar, 26 ± 3 vs. AC-Parkhill, 35 ± 4, P < 0.05) and pearling (WG, 26 ± 4 vs. WP 35 ± 3, P < 0.05). When two cultivars were milled and processed to wet pasta the GI increased by 184% (P < 0.05). The pearled wet pasta had a significantly lower GI compared to the whole grain (P < 0.05). Boiled barley kernels tended to elicit greater satiety than white bread, but the difference was not significant. In both the boiled barley kernels and the wet pasta, pearling did not affect the MW, viscosity and solubility. MW did not significantly differ between cultivars but solubility and viscosity did (P < 0.05). The wet pasta had significantly lower MW, solubility, viscosity but not β-glucan content than the boiled barley kernels (P < 0.05). In conclusion, pearling did not have an effect but milling and extruding resulted in significant reduction in MW, solubility and viscosity. The GI of barley is influenced significantly by cultivar, pearling and milling. Further studies are required to determine the effect on satiety.Ph