FACTORS AFFECTING VISCOSITY OF SLURRIES OF OAT GROAT FLOURS

Oat grain is routinely kilned and steamed before milling to develop fl avor and to inactivate lipid-degrading enzymes. Heat treatments can si gnificantly affect viscous properties, which have functional and nutri tional importance. Oat flour slurries (23%, w/w, solids dry basis) mad e from steamed (for 20 min) or autoclaved (at 121 degrees C, 15 psi, f or 10 min) grain developed high viscosities, whereas flour slurries ma de from raw or kilned (105 degrees C for 90 min) oats did not. Flour s lurries made from raw greats, surface-sterilized by 1% hypochlorite, w ere more. viscous than untreated raw great flour slurries, suggesting that beta-glucan hydrolases on the surface of the groat caused the vis cosity losses observed in raw or kilned greats. However, because visco sities developed by surface-sterilized greats were not as great as in steamed oat-flour slurries and because some roasting treatments also i nactivated enzymes without enhancing viscosity, it appears steaming mi ght also affect the beta-glucan polymer, resulting in its greater hydr ation in solution. Smaller particle size and higher incubation tempera ture also resulted in increased flour slurry viscosity, presumably bec ause of increased hydration of the beta-glucan. Rmoval of lipids from steamed oat flour significantly increased the oat flour slurry viscosi ty, apparently by increasing the beta-glucan concentration in the flou r.