Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/7/1997
Publication Date: N/A
Citation: Interpretive Summary: Oat had long been considered as a healthy food. During the processing of raw oat in preparation for milling, grain is oven roasted (kilned) and steamed to stabilize the lipid components, and to develop flavor. We have investigated the effects of heat-treatments on the viscosity of oat flour slurries. Not only are the rheological properties of the oat flour important as a functional property of oat in food products, but it is believed that the highly viscous nature of oat flour slurries are responsible for the cholesterol-lowering effect that oat products have when incorporated in the human diet. We have found that oat flour slurries made from steamed oats develop a high viscosity, whereas, slurries made from raw or kilned oats do not. Steaming times of only 5 min, or autoclaving the oat was adequate for allowing the high viscosity to develop. We have also found that surface sterilizing raw oats with a dilute bleach solution allowed for the formation of more viscosity that formed in raw oats. This suggests that enzymes either on the surface of the oat or in microorganisms on the oat may contribute to the loss of viscosity observed in raw oat slurries. We have also found that smaller particle size and higher incubation temperature generated higher slurry viscosity. Removal of lipids from steamed oat flour significantly increased the oat flour slurry viscosity, apparently simply by increasing the beta-glucan concentration in the flour.
Technical Abstract: Oat grain is routinely kilned and steamed before milling to develop flavor and to inactiviate lipid-degrading enzymes. Heat treatments can significantly affect viscous properties, which have functional and nutritional importance. Oat flour slurries (23% solids) made from steamed or autoclaved grain developed high viscosities, whereas, flour slurries made from raw or kilned oats did not. Flour slurries made from surface sterilized raw groats developed more viscosity than raw groats, suggesting that beta-glucan hydrolyzing enzymes, either on the surface of the groat, or in microorganisms on the groat, may be responsible for part of the viscosity losses observed in raw or kilned groats. However, because viscosities developed in surface sterilized groats was not as great as in steamed oat flour slurries, it appears that steaming also affects the beta-glucan polymer, in an unidentified way that results in its greater hydration in solution. Smaller particle size and higher incubation temperature also resulted in increased flour slurry viscosity, presumably because of increased hydration of the beta-glucan. Removal of lipids from steamed oat flour significantly increased the oat flour slurry viscosity, apparently by increasing the beta-glucan concentration in the flour.