Submitted to: Cereal Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/15/1998
Publication Date: N/A
Citation: Interpretive Summary: Studies have indicated that including oat bran in your diet can lower your blood cholesterol and reduce your risk of heart disease. It has been suggested that the soluble fiber component of oat bran, largely composed of beta-glucans, makes the contents of the gut more viscous, which inhibits the absorption of cholesterol. We have found that heat-treatments routinely applied to oat grain, such as roasting and steaming, dramatically affects the viscosity of beta-glucans extracted from oats, which may in turn affect their ability to affect blood cholesterol. Steaming of grain greatly enhances the viscosity of beta-glucan extracts, while roasting decreases the viscosity of extracts. It appears that steaming affects the way that the beta-glucan binds to itself, allowing the polymer to interact more with water in solution, resulting in a greater viscosity. Roasting makes the beta-glucan molecule bind more with itself and less with water, resulting in less viscosity in solutions. We may be able to increase the cholesterol lowering potential of oat products by changing the heat-treatments the grain or flour is exposed to during processing.
Technical Abstract: Effects of hydrothermal treatments (steaming, roasting) of oat grain on beta-glucan extractability and rheological properties were tested on oat cultivars with low (Robert) and high (Marion) beta-glucan content. Steaming of grain reduced the amount of beta-glucan that could be extracted, compared with raw or roasted grain, but the extracts from steamed grain had much greater viscosity. Increased extraction temperatures increased the amount and the average relative molecular mass of beta-glucans extracted. In boiling water extractions, the average relative molecular mass among raw, roasted and steamed oat samples were equivalent, but extracts from steamed oat grain had significantly higher intrinsic viscosity than the extracts from roasted or raw oat grains. Beta-glucan solutions purified from steamed grain extracts were very viscous and highly pseudoplastic as described by the power law equation. Oat beta-glucans from steamed samples were more viscoelastic than beta-glucans from roasted or raw oat samples. Because viscous properties of beta-glucans are influenced by hydrothermal treatments without affecting polymer molecular weight, polymer interaction with the solvent must be affected. Steaming may disrupt intramolecular cross-linkings in native beta-glucan, allowing a linear chain configuration to generate greater viscosity.