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The efficacy of ß-glucan in a food in lowering blood cholesterol and glucose is largely related to its viscosity which is a function of its content and molecular structure. This study investigated viscosity of ß-glucan in relation to its content and molecular properties in 147 barley samples. Preliminarily experiments were carried out to inactivate ß-glucan degrading enzymes in barley in order to be able to measure viscosity of ß-glucan. Dry heat, microwave heating and boiling in buffer were evaluated as a means to inactivate enzymes in barley with the use of pure ß-glucan as a substrate. The viscosity of ß-glucan significantly dropped over time (120 min) in the presence of unheated barley flour. Heating barley flour at 130oC for 120 min or microwaving for 20 min was not enough to avoid degradation of ß-glucan. However, boiling barley flour for 10 min was effective in inactivating ß-glucan degrading enzymes as indicated by preserving the viscosity of ß-glucan. Viscosity of ß-glucan in boiled barleys was measured based on the newly developed AACCI method 32-24.01. The sample weight of barley flour was adjusted to provide at least 1% ß-glucan slurry in the RVA canister and therefore variations in viscosity among barley samples are related to content and molecular properties of ß-glucan. Viscosity was measured at 37oC, monitored over the test time (120 min) and presented at three points (V10, V25 and V75) which represent the three stages of viscosity development (sharp, gradual and steady increase). The barley samples contained ß-glucan ranging from 8.2-12.1% with an Mw range from 43,367 to 623,164 g/mol and a viscosity range 231-2191, 326-2575 and 394-2912 cP for V10, V25 and V75, respectively. The results indicate that ß-glucan viscosity would be more effective in the development of functional food barleys.