Effect of hydrothermal and enzymic treatments on the viscous behavior of dry- and wet-milled oat brans

The effect of hydrothermal, Termamyl alpha-amylase, and Finase S40 phytase treatments on viscous behavior of dry- and wet-milled oat brans was studied. Regular oat bran from a dry-milling procedure was higher in starch and lower in beta-glucan and other dietary fibers than the fiber-concentrated oat bran from a wet- milling procedure. The high content of dietary fibers, especially beta-glucan, in the wet-milled oat bran had a marked effect on the viscosity of heat- and alpha-amylase-treated bran slurries. Heating increased the amount of soluble beta-glucan, on average, from 29 to 84%. The molecular weight of beta-glucan was 8.4 x 10(5) in regular oat bran and 6.0 x 10(5) in fiber-concentrated oat bran, and it remained unchanged during the hydrothermal and alpha- amylase treatments. The phytase preparation used for hydrolysis of phytic acid also caused a reduction in viscosity of oat bran slurries. When the phytase preparation was added before heating, the viscosity of bran slurries remained at low levels during the whole temperature cycle, owing mainly to degradation of beta- glucan. Rapid reduction in viscosity in the postheating treatments with phytase preparation was caused by the degradation of gelatinized starch together with beta-glucan. During both treatments with phytase preparation, the amount of soluble beta- glucan increased to 90%. Phytic acid content in the bran slurries decreased more (54%) in the postheating treatment than in the preheating treatment with Finase S40 phytase (36%). Enzymic studies showed that, at high levels of nonstarch polysaccharides, the viscosity of oat bran slurries changes only a little when starch is completely degraded to water-soluble oligosaccharides; but the viscosity clearly decreases when beta-glucan is only partially hydrolyzed to high molecular weight products (Mw 4.0 x 10(4))